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proc(5)                       File Formats Manual                      proc(5)

NAME
       proc - process information pseudo-filesystem

DESCRIPTION
       The  proc filesystem is a pseudo-filesystem which provides an interface
       to kernel data structures.  It is commonly  mounted  at  /proc.   Typi-
       cally,  it  is  mounted automatically by the system, but it can also be
       mounted manually using a command such as:

           mount -t proc proc /proc

       Most of the files in the proc filesystem are read-only, but some  files
       are writable, allowing kernel variables to be changed.

   Mount options
       The proc filesystem supports the following mount options:

       hidepid=n (since Linux 3.3)
              This option controls who can access the information in /proc/pid
              directories.  The argument, n, is one of the following values:

              0   Everybody may access all /proc/pid directories.  This is the
                  traditional  behavior,  and the default if this mount option
                  is not specified.

              1   Users may not access files  and  subdirectories  inside  any
                  /proc/pid  directories but their own (the /proc/pid directo-
                  ries themselves remain visible).  Sensitive  files  such  as
                  /proc/pid/cmdline  and  /proc/pid/status  are  now protected
                  against other users.  This  makes  it  impossible  to  learn
                  whether  any  user is running a specific program (so long as
                  the program doesn't otherwise reveal itself  by  its  behav-
                  ior).

              2   As for mode 1, but in addition the /proc/pid directories be-
                  longing to other users become invisible.   This  means  that
                  /proc/pid entries can no longer be used to discover the PIDs
                  on the system.  This doesn't hide the fact  that  a  process
                  with a specific PID value exists (it can be learned by other
                  means, for example, by "kill  -0  $PID"),  but  it  hides  a
                  process's  UID  and GID, which could otherwise be learned by
                  employing stat(2) on a /proc/pid  directory.   This  greatly
                  complicates  an  attacker's  task  of  gathering information
                  about running processes (e.g., discovering whether some dae-
                  mon  is  running  with  elevated privileges, whether another
                  user is running some sensitive program, whether other  users
                  are running any program at all, and so on).

       gid=gid (since Linux 3.3)
              Specifies  the  ID  of  a  group whose members are authorized to
              learn process information otherwise prohibited by hidepid (i.e.,
              users  in  this  group  behave  as though /proc was mounted with
              hidepid=0).  This group should be  used  instead  of  approaches
              such as putting nonroot users into the sudoers(5) file.

   Overview
       Underneath  /proc,  there are the following general groups of files and
       subdirectories:

       /proc/pid subdirectories
              Each one of these subdirectories contains files and  subdirecto-
              ries exposing information about the process with the correspond-
              ing process ID.

              Underneath each of the /proc/pid directories, a  task  subdirec-
              tory contains subdirectories of the form task/tid, which contain
              corresponding information about  each  of  the  threads  in  the
              process, where tid is the kernel thread ID of the thread.

              The  /proc/pid subdirectories are visible when iterating through
              /proc with getdents(2) (and thus are visible when one uses ls(1)
              to view the contents of /proc).

       /proc/tid subdirectories
              Each  one of these subdirectories contains files and subdirecto-
              ries exposing information about the thread with the  correspond-
              ing  thread  ID.  The contents of these directories are the same
              as the corresponding /proc/pid/task/tid directories.

              The /proc/tid subdirectories  are  not  visible  when  iterating
              through  /proc  with  getdents(2) (and thus are not visible when
              one uses ls(1) to view the contents of /proc).

       /proc/self
              When a process accesses this magic symbolic link, it resolves to
              the process's own /proc/pid directory.

       /proc/thread-self
              When  a thread accesses this magic symbolic link, it resolves to
              the process's own /proc/self/task/tid directory.

       /proc/[a-z]*
              Various other files and subdirectories under /proc  expose  sys-
              tem-wide information.

       All of the above are described in more detail below.

   Files and directories
       The  following  list provides details of many of the files and directo-
       ries under the /proc hierarchy.

       /proc/pid
              There is a numerical subdirectory for each running process;  the
              subdirectory  is named by the process ID.  Each /proc/pid subdi-
              rectory contains the pseudo-files and directories described  be-
              low.

              The  files inside each /proc/pid directory are normally owned by
              the effective user and effective group ID of the process.   How-
              ever,  as a security measure, the ownership is made root:root if
              the process's "dumpable" attribute is set to a value other  than
              1.

              Before Linux 4.11, root:root meant the "global" root user ID and
              group ID (i.e., UID 0 and GID 0 in the initial user  namespace).
              Since  Linux  4.11, if the process is in a noninitial user name-
              space that has a valid mapping for user (group) ID 0 inside  the
              namespace,  then  the  user (group) ownership of the files under
              /proc/pid is instead made the same as the root user  (group)  ID
              of  the  namespace.   This means that inside a container, things
              work as expected for the container "root" user.

              The process's "dumpable" attribute may change for the  following
              reasons:

              •  The   attribute   was   explicitly   set   via  the  prctl(2)
                 PR_SET_DUMPABLE operation.

              •  The  attribute  was  reset  to  the   value   in   the   file
                 /proc/sys/fs/suid_dumpable (described below), for the reasons
                 described in prctl(2).

              Resetting the "dumpable" attribute to 1 reverts the ownership of
              the  /proc/pid/*  files  to the process's effective UID and GID.
              Note, however, that if the effective UID or GID is  subsequently
              modified,  then  the  "dumpable"  attribute may be reset, as de-
              scribed in prctl(2).  Therefore, it may be  desirable  to  reset
              the "dumpable" attribute after making any desired changes to the
              process's effective UID or GID.

       /proc/pid/attr
              The files in this directory provide an API for security modules.
              The  contents  of  this directory are files that can be read and
              written in order to set security-related attributes.   This  di-
              rectory was added to support SELinux, but the intention was that
              the API be general enough to  support  other  security  modules.
              For  the  purpose  of  explanation, examples of how SELinux uses
              these files are provided below.

              This directory is present only if the kernel was configured with
              CONFIG_SECURITY.

       /proc/pid/attr/current (since Linux 2.6.0)
              The  contents  of  this  file represent the current security at-
              tributes of the process.

              In SELinux, this file is used to get the security context  of  a
              process.   Prior to Linux 2.6.11, this file could not be used to
              set the security context (a  write  was  always  denied),  since
              SELinux  limited  process security transitions to execve(2) (see
              the description of  /proc/pid/attr/exec,  below).   Since  Linux
              2.6.11,  SELinux  lifted  this  restriction and began supporting
              "set" operations via writes to this node if authorized  by  pol-
              icy,  although use of this operation is only suitable for appli-
              cations that are trusted to maintain any desired separation  be-
              tween the old and new security contexts.

              Prior  to  Linux  2.6.28, SELinux did not allow threads within a
              multithreaded process to set their  security  context  via  this
              node  as it would yield an inconsistency among the security con-
              texts of the threads sharing the same memory space.  Since Linux
              2.6.28,  SELinux  lifted  this  restriction and began supporting
              "set" operations for threads within a multithreaded  process  if
              the new security context is bounded by the old security context,
              where the bounded relation is defined in policy  and  guarantees
              that the new security context has a subset of the permissions of
              the old security context.

              Other security modules may choose to  support  "set"  operations
              via writes to this node.

       /proc/pid/attr/exec (since Linux 2.6.0)
              This  file  represents  the  attributes to assign to the process
              upon a subsequent execve(2).

              In SELinux, this is needed to support  role/domain  transitions,
              and  execve(2)  is  the preferred point to make such transitions
              because it offers better control over the initialization of  the
              process  in the new security label and the inheritance of state.
              In SELinux, this attribute is reset on execve(2) so that the new
              program  reverts to the default behavior for any execve(2) calls
              that it may make.  In SELinux, a process can set  only  its  own
              /proc/pid/attr/exec attribute.

       /proc/pid/attr/fscreate (since Linux 2.6.0)
              This  file  represents the attributes to assign to files created
              by  subsequent  calls  to  open(2),  mkdir(2),  symlink(2),  and
              mknod(2)

              SELinux  employs  this file to support creation of a file (using
              the aforementioned system calls) in  a  secure  state,  so  that
              there  is no risk of inappropriate access being obtained between
              the time of creation and the time that attributes are  set.   In
              SELinux,  this  attribute is reset on execve(2), so that the new
              program reverts to the default behavior for  any  file  creation
              calls  it may make, but the attribute will persist across multi-
              ple file creation calls within a program unless it is explicitly
              reset.    In   SELinux,   a   process   can  set  only  its  own
              /proc/pid/attr/fscreate attribute.

       /proc/pid/attr/keycreate (since Linux 2.6.18)
              If a process writes a security context into this file, all  sub-
              sequently  created  keys  (add_key(2)) will be labeled with this
              context.  For further information, see the  kernel  source  file
              Documentation/security/keys/core.rst  (or file Documentation/se-
              curity/keys.txt between Linux 3.0 and Linux 4.13, or  Documenta-
              tion/keys.txt before Linux 3.0).

       /proc/pid/attr/prev (since Linux 2.6.0)
              This  file  contains  the security context of the process before
              the  last  execve(2);   that   is,   the   previous   value   of
              /proc/pid/attr/current.

       /proc/pid/attr/socketcreate (since Linux 2.6.18)
              If  a process writes a security context into this file, all sub-
              sequently created sockets will be labeled with this context.

       /proc/pid/autogroup (since Linux 2.6.38)
              See sched(7).

       /proc/pid/auxv (since Linux 2.6.0)
              This contains the contents of the  ELF  interpreter  information
              passed  to the process at exec time.  The format is one unsigned
              long ID plus one unsigned long value for each entry.   The  last
              entry contains two zeros.  See also getauxval(3).

              Permission  to  access  this file is governed by a ptrace access
              mode PTRACE_MODE_READ_FSCREDS check; see ptrace(2).

       /proc/pid/cgroup (since Linux 2.6.24)
              See cgroups(7).

       /proc/pid/clear_refs (since Linux 2.6.22)

              This is a  write-only  file,  writable  only  by  owner  of  the
              process.

              The following values may be written to the file:

              1 (since Linux 2.6.22)
                     Reset  the  PG_Referenced and ACCESSED/YOUNG bits for all
                     the pages associated with  the  process.   (Before  Linux
                     2.6.32,  writing  any nonzero value to this file had this
                     effect.)

              2 (since Linux 2.6.32)
                     Reset the PG_Referenced and ACCESSED/YOUNG bits  for  all
                     anonymous pages associated with the process.

              3 (since Linux 2.6.32)
                     Reset  the  PG_Referenced and ACCESSED/YOUNG bits for all
                     file-mapped pages associated with the process.

              Clearing the PG_Referenced and ACCESSED/YOUNG  bits  provides  a
              method to measure approximately how much memory a process is us-
              ing.  One first inspects the values in the  "Referenced"  fields
              for the VMAs shown in /proc/pid/smaps to get an idea of the mem-
              ory footprint of the process.  One then clears the PG_Referenced
              and  ACCESSED/YOUNG bits and, after some measured time interval,
              once again inspects the values in the "Referenced" fields to get
              an  idea of the change in memory footprint of the process during
              the measured interval.  If one is interested only in  inspecting
              the  selected  mapping  types, then the value 2 or 3 can be used
              instead of 1.

              Further values can be written to affect different properties:

              4 (since Linux 3.11)
                     Clear the soft-dirty bit for  all  the  pages  associated
                     with  the  process.   This  is  used (in conjunction with
                     /proc/pid/pagemap) by the check-point restore  system  to
                     discover which pages of a process have been dirtied since
                     the file /proc/pid/clear_refs was written to.

              5 (since Linux 4.0)
                     Reset the peak resident set size ("high water  mark")  to
                     the process's current resident set size value.

              Writing  any  value  to  /proc/pid/clear_refs  other  than those
              listed above has no effect.

              The /proc/pid/clear_refs  file  is  present  only  if  the  CON-
              FIG_PROC_PAGE_MONITOR kernel configuration option is enabled.

       /proc/pid/cmdline
              This  read-only  file  holds  the  complete command line for the
              process, unless the process is a zombie.  In  the  latter  case,
              there is nothing in this file: that is, a read on this file will
              return 0 characters.  The command-line arguments appear in  this
              file  as a set of strings separated by null bytes ('\0'), with a
              further null byte after the last string.

              If, after an execve(2), the process modifies its  argv  strings,
              those  changes will show up here.  This is not the same thing as
              modifying the argv array.

              Furthermore, a process may change the memory location that  this
              file refers via prctl(2) operations such as PR_SET_MM_ARG_START.

              Think  of  this  file as the command line that the process wants
              you to see.

       /proc/pid/comm (since Linux 2.6.33)
              This file exposes the process's comm value—that is, the  command
              name associated with the process.  Different threads in the same
              process  may  have  different  comm   values,   accessible   via
              /proc/pid/task/tid/comm.  A thread may modify its comm value, or
              that of any of other thread in the same thread  group  (see  the
              discussion  of CLONE_THREAD in clone(2)), by writing to the file
              /proc/self/task/tid/comm.   Strings  longer  than  TASK_COMM_LEN
              (16)  characters  (including  the  terminating  null  byte)  are
              silently truncated.

              This file provides a superset of the  prctl(2)  PR_SET_NAME  and
              PR_GET_NAME operations, and is employed by pthread_setname_np(3)
              when used to rename threads other than the caller.  The value in
              this  file  is  used  for  the  %e  specifier  in /proc/sys/ker-
              nel/core_pattern; see core(5).

       /proc/pid/coredump_filter (since Linux 2.6.23)
              See core(5).

       /proc/pid/cpuset (since Linux 2.6.12)
              See cpuset(7).

       /proc/pid/cwd
              This is a symbolic link to the current working directory of  the
              process.   To  find out the current working directory of process
              20, for instance, you can do this:

                  $ cd /proc/20/cwd; pwd -P

              In a multithreaded process, the contents of this  symbolic  link
              are  not  available  if  the  main thread has already terminated
              (typically by calling pthread_exit(3)).

              Permission to dereference or read  (readlink(2))  this  symbolic
              link  is  governed  by a ptrace access mode PTRACE_MODE_READ_FS-
              CREDS check; see ptrace(2).

       /proc/pid/environ
              This file contains the initial environment that was set when the
              currently  executing program was started via execve(2).  The en-
              tries are separated by null bytes ('\0'), and  there  may  be  a
              null  byte  at  the  end.  Thus, to print out the environment of
              process 1, you would do:

                  $ cat /proc/1/environ | tr '\000' '\n'

              If, after an execve(2), the  process  modifies  its  environment
              (e.g.,  by  calling functions such as putenv(3) or modifying the
              environ(7) variable directly), this file will not reflect  those
              changes.

              Furthermore,  a process may change the memory location that this
              file refers via prctl(2) operations such as PR_SET_MM_ENV_START.

              Permission to access this file is governed by  a  ptrace  access
              mode PTRACE_MODE_READ_FSCREDS check; see ptrace(2).

       /proc/pid/exe
              Under Linux 2.2 and later, this file is a symbolic link contain-
              ing the actual pathname of the executed command.  This  symbolic
              link  can  be  dereferenced normally; attempting to open it will
              open the executable.  You can even type /proc/pid/exe to run an-
              other  copy  of the same executable that is being run by process
              pid.  If the pathname has been unlinked, the symbolic link  will
              contain  the  string  '(deleted)' appended to the original path-
              name.  In a multithreaded process, the contents of this symbolic
              link are not available if the main thread has already terminated
              (typically by calling pthread_exit(3)).

              Permission to dereference or read  (readlink(2))  this  symbolic
              link  is  governed  by a ptrace access mode PTRACE_MODE_READ_FS-
              CREDS check; see ptrace(2).

              Under Linux 2.0 and earlier, /proc/pid/exe is a pointer  to  the
              binary  which  was  executed, and appears as a symbolic link.  A
              readlink(2) call on this file under Linux 2.0 returns  a  string
              in the format:

                  [device]:inode

              For  example, [0301]:1502 would be inode 1502 on device major 03
              (IDE, MFM, etc. drives) minor 01 (first partition on  the  first
              drive).

              find(1) with the -inum option can be used to locate the file.

       /proc/pid/fd/
              This  is a subdirectory containing one entry for each file which
              the process has open, named by its file descriptor, and which is
              a  symbolic link to the actual file.  Thus, 0 is standard input,
              1 standard output, 2 standard error, and so on.

              For file descriptors for pipes and sockets, the entries will  be
              symbolic links whose content is the file type with the inode.  A
              readlink(2) call on this file returns a string in the format:

                  type:[inode]

              For example, socket:[2248868] will be a socket and its inode  is
              2248868.   For  sockets, that inode can be used to find more in-
              formation in one of the files under /proc/net/.

              For file descriptors that have  no  corresponding  inode  (e.g.,
              file    descriptors   produced   by   bpf(2),   epoll_create(2),
              eventfd(2),  inotify_init(2),  perf_event_open(2),  signalfd(2),
              timerfd_create(2), and userfaultfd(2)), the entry will be a sym-
              bolic link with contents of the form

                  anon_inode:file-type

              In many cases (but not all),  the  file-type  is  surrounded  by
              square brackets.

              For  example, an epoll file descriptor will have a symbolic link
              whose content is the string anon_inode:[eventpoll].

              In a multithreaded process, the contents of this  directory  are
              not  available  if the main thread has already terminated (typi-
              cally by calling pthread_exit(3)).

              Programs that take a filename as a  command-line  argument,  but
              don't take input from standard input if no argument is supplied,
              and programs that write to a file named as a command-line  argu-
              ment, but don't send their output to standard output if no argu-
              ment is supplied, can nevertheless be made to use standard input
              or  standard  output by using /proc/pid/fd files as command-line
              arguments.  For example, assuming that -i is the flag  designat-
              ing an input file and -o is the flag designating an output file:

                  $ foobar -i /proc/self/fd/0 -o /proc/self/fd/1 ...

              and you have a working filter.

              /proc/self/fd/N  is  approximately the same as /dev/fd/N in some
              UNIX and UNIX-like systems.  Most Linux MAKEDEV scripts symboli-
              cally link /dev/fd to /proc/self/fd, in fact.

              Most systems provide symbolic links /dev/stdin, /dev/stdout, and
              /dev/stderr, which respectively link to the files 0, 1, and 2 in
              /proc/self/fd.   Thus the example command above could be written
              as:

                  $ foobar -i /dev/stdin -o /dev/stdout ...

              Permission to dereference or  read  (readlink(2))  the  symbolic
              links  in  this  directory  is  governed by a ptrace access mode
              PTRACE_MODE_READ_FSCREDS check; see ptrace(2).

              Note that for file descriptors referring to  inodes  (pipes  and
              sockets, see above), those inodes still have permission bits and
              ownership information distinct from those  of  the  /proc/pid/fd
              entry, and that the owner may differ from the user and group IDs
              of the process.  An unprivileged process may lack permissions to
              open them, as in this example:

                  $ echo test | sudo -u nobody cat
                  test
                  $ echo test | sudo -u nobody cat /proc/self/fd/0
                  cat: /proc/self/fd/0: Permission denied

              File  descriptor  0  refers to the pipe created by the shell and
              owned by that shell's user, which is not nobody, so cat does not
              have  permission  to  create  a new file descriptor to read from
              that inode, even though it can still read from its existing file
              descriptor 0.

       /proc/pid/fdinfo/ (since Linux 2.6.22)
              This  is a subdirectory containing one entry for each file which
              the process has open, named by its file descriptor.   The  files
              in this directory are readable only by the owner of the process.
              The contents of each file can  be  read  to  obtain  information
              about the corresponding file descriptor.  The content depends on
              the type of file referred to by the corresponding file  descrip-
              tor.

              For regular files and directories, we see something like:

                  $ cat /proc/12015/fdinfo/4
                  pos:    1000
                  flags:  01002002
                  mnt_id: 21

              The fields are as follows:

              pos    This is a decimal number showing the file offset.

              flags  This  is  an  octal  number that displays the file access
                     mode and file status flags (see open(2)).  If the  close-
                     on-exec file descriptor flag is set, then flags will also
                     include the value O_CLOEXEC.

                     Before Linux 3.1, this field  incorrectly  displayed  the
                     setting  of  O_CLOEXEC  at  the time the file was opened,
                     rather than the  current  setting  of  the  close-on-exec
                     flag.

              mnt_id This  field,  present  since Linux 3.15, is the ID of the
                     mount containing  this  file.   See  the  description  of
                     /proc/pid/mountinfo.

              For  eventfd  file  descriptors  (see eventfd(2)), we see (since
              Linux 3.8) the following fields:

                  pos: 0
                  flags:    02
                  mnt_id:   10
                  eventfd-count:               40

              eventfd-count is the current value of the  eventfd  counter,  in
              hexadecimal.

              For  epoll  file descriptors (see epoll(7)), we see (since Linux
              3.8) the following fields:

                  pos: 0
                  flags:    02
                  mnt_id:   10
                  tfd:        9 events:       19 data: 74253d2500000009
                  tfd:        7 events:       19 data: 74253d2500000007

              Each of the lines beginning tfd describes one of  the  file  de-
              scriptors  being  monitored  via  the epoll file descriptor (see
              epoll_ctl(2) for some details).  The tfd field is the number  of
              the  file descriptor.  The events field is a hexadecimal mask of
              the events being monitored for this file descriptor.   The  data
              field is the data value associated with this file descriptor.

              For  signalfd  file descriptors (see signalfd(2)), we see (since
              Linux 3.8) the following fields:

                  pos: 0
                  flags:    02
                  mnt_id:   10
                  sigmask:  0000000000000006

              sigmask is the hexadecimal mask of signals that are accepted via
              this  signalfd  file descriptor.  (In this example, bits 2 and 3
              are set, corresponding to the signals SIGINT  and  SIGQUIT;  see
              signal(7).)

              For  inotify  file  descriptors  (see inotify(7)), we see (since
              Linux 3.8) the following fields:

                  pos: 0
                  flags:    00
                  mnt_id:   11
                  inotify wd:2 ino:7ef82a sdev:800001 mask:800afff ignored_mask:0 fhandle-bytes:8 fhandle-type:1 f_handle:2af87e00220ffd73
                  inotify wd:1 ino:192627 sdev:800001 mask:800afff ignored_mask:0 fhandle-bytes:8 fhandle-type:1 f_handle:27261900802dfd73

              Each of the lines beginning with "inotify" displays  information
              about one file or directory that is being monitored.  The fields
              in this line are as follows:

              wd     A watch descriptor number (in decimal).

              ino    The inode number of the target file (in hexadecimal).

              sdev   The ID of the device where the target  file  resides  (in
                     hexadecimal).

              mask   The  mask  of  events being monitored for the target file
                     (in hexadecimal).

              If the kernel was built with exportfs support, the path  to  the
              target  file  is exposed as a file handle, via three hexadecimal
              fields: fhandle-bytes, fhandle-type, and f_handle.

              For fanotify file descriptors (see fanotify(7)), we  see  (since
              Linux 3.8) the following fields:

                  pos: 0
                  flags:    02
                  mnt_id:   11
                  fanotify flags:0 event-flags:88002
                  fanotify ino:19264f sdev:800001 mflags:0 mask:1 ignored_mask:0 fhandle-bytes:8 fhandle-type:1 f_handle:4f261900a82dfd73

              The  fourth  line displays information defined when the fanotify
              group was created via fanotify_init(2):

              flags  The flags argument given to  fanotify_init(2)  (expressed
                     in hexadecimal).

              event-flags
                     The event_f_flags argument given to fanotify_init(2) (ex-
                     pressed in hexadecimal).

              Each additional line shown  in  the  file  contains  information
              about  one  of  the  marks in the fanotify group.  Most of these
              fields are as for inotify, except:

              mflags The flags associated with the mark (expressed in hexadec-
                     imal).

              mask   The events mask for this mark (expressed in hexadecimal).

              ignored_mask
                     The  mask  of  events that are ignored for this mark (ex-
                     pressed in hexadecimal).

              For details on these fields, see fanotify_mark(2).

              For timerfd file descriptors (see  timerfd(2)),  we  see  (since
              Linux 3.17) the following fields:

                  pos:    0
                  flags:  02004002
                  mnt_id: 13
                  clockid: 0
                  ticks: 0
                  settime flags: 03
                  it_value: (7695568592, 640020877)
                  it_interval: (0, 0)

              clockid
                     This  is the numeric value of the clock ID (corresponding
                     to one of the CLOCK_*  constants  defined  via  <time.h>)
                     that  is  used to mark the progress of the timer (in this
                     example, 0 is CLOCK_REALTIME).

              ticks  This is the number of timer  expirations  that  have  oc-
                     curred,  (i.e.,  the  value  that read(2) on it would re-
                     turn).

              settime flags
                     This field lists the flags with  which  the  timerfd  was
                     last  armed  (see  timerfd_settime(2)), in octal (in this
                     example,  both   TFD_TIMER_ABSTIME   and   TFD_TIMER_CAN-
                     CEL_ON_SET are set).

              it_value
                     This  field  contains  the amount of time until the timer
                     will next expire, expressed in seconds  and  nanoseconds.
                     This  is always expressed as a relative value, regardless
                     of whether the timer was created using the  TFD_TIMER_AB-
                     STIME flag.

              it_interval
                     This field contains the interval of the timer, in seconds
                     and nanoseconds.  (The it_value  and  it_interval  fields
                     contain  the  values that timerfd_gettime(2) on this file
                     descriptor would return.)

       /proc/pid/gid_map (since Linux 3.5)
              See user_namespaces(7).

       /proc/pid/io (since Linux 2.6.20)
              This file contains I/O statistics for the process, for example:

                  # cat /proc/3828/io
                  rchar: 323934931
                  wchar: 323929600
                  syscr: 632687
                  syscw: 632675
                  read_bytes: 0
                  write_bytes: 323932160
                  cancelled_write_bytes: 0

              The fields are as follows:

              rchar: characters read
                     The number of bytes which this task has caused to be read
                     from storage.  This is simply the sum of bytes which this
                     process passed to read(2) and similar system  calls.   It
                     includes things such as terminal I/O and is unaffected by
                     whether or not actual physical disk I/O was required (the
                     read might have been satisfied from pagecache).

              wchar: characters written
                     The  number of bytes which this task has caused, or shall
                     cause to be written to disk.  Similar caveats apply  here
                     as with rchar.

              syscr: read syscalls
                     Attempt  to  count the number of read I/O operations—that
                     is, system calls such as read(2) and pread(2).

              syscw: write syscalls
                     Attempt to count the number of write I/O  operations—that
                     is, system calls such as write(2) and pwrite(2).

              read_bytes: bytes read
                     Attempt  to  count the number of bytes which this process
                     really did cause to be fetched from  the  storage  layer.
                     This is accurate for block-backed filesystems.

              write_bytes: bytes written
                     Attempt  to  count the number of bytes which this process
                     caused to be sent to the storage layer.

              cancelled_write_bytes:
                     The big inaccuracy here is truncate.  If a process writes
                     1 MB to a file and then deletes the file, it will in fact
                     perform no writeout.  But it will have been accounted  as
                     having  caused 1 MB of write.  In other words: this field
                     represents the number of bytes which this process  caused
                     to not happen, by truncating pagecache.  A task can cause
                     "negative" I/O too.  If this task  truncates  some  dirty
                     pagecache, some I/O which another task has been accounted
                     for (in its write_bytes) will not be happening.

              Note: In the current implementation, things are a  bit  racy  on
              32-bit  systems:  if  process  A  reads process B's /proc/pid/io
              while process B  is  updating  one  of  these  64-bit  counters,
              process A could see an intermediate result.

              Permission  to  access  this file is governed by a ptrace access
              mode PTRACE_MODE_READ_FSCREDS check; see ptrace(2).

       /proc/pid/limits (since Linux 2.6.24)
              This file displays the soft limit, hard limit, and units of mea-
              surement  for  each  of the process's resource limits (see getr-
              limit(2)).  Up to and including Linux 2.6.35, this file is  pro-
              tected  to  allow  reading  only by the real UID of the process.
              Since Linux 2.6.36, this file is readable by all  users  on  the
              system.

       /proc/pid/map_files/ (since Linux 3.3)
              This  subdirectory  contains  entries  corresponding  to memory-
              mapped files (see mmap(2)).  Entries are named by memory  region
              start  and  end address pair (expressed as hexadecimal numbers),
              and are symbolic links to the mapped files themselves.  Here  is
              an example, with the output wrapped and reformatted to fit on an
              80-column display:

                  # ls -l /proc/self/map_files/
                  lr--------. 1 root root 64 Apr 16 21:31
                              3252e00000-3252e20000 -> /usr/lib64/ld-2.15.so
                  ...

              Although these entries are present for memory regions that  were
              mapped  with  the MAP_FILE flag, the way anonymous shared memory
              (regions created with the MAP_ANON | MAP_SHARED flags) is imple-
              mented  in Linux means that such regions also appear on this di-
              rectory.  Here is an  example  where  the  target  file  is  the
              deleted /dev/zero one:

                  lrw-------. 1 root root 64 Apr 16 21:33
                              7fc075d2f000-7fc075e6f000 -> /dev/zero (deleted)

              Permission  to  access  this file is governed by a ptrace access
              mode PTRACE_MODE_READ_FSCREDS check; see ptrace(2).

              Until Linux 4.3,  this  directory  appeared  only  if  the  CON-
              FIG_CHECKPOINT_RESTORE kernel configuration option was enabled.

              Capabilities  are  required to read the contents of the symbolic
              links in this directory: before Linux 5.9, the  reading  process
              requires  CAP_SYS_ADMIN  in  the  initial  user namespace; since
              Linux 5.9, the reading process must have either CAP_SYS_ADMIN or
              CAP_CHECKPOINT_RESTORE in the user namespace where it resides.

       /proc/pid/maps
              A  file containing the currently mapped memory regions and their
              access permissions.  See mmap(2) for  some  further  information
              about memory mappings.

              Permission  to  access  this file is governed by a ptrace access
              mode PTRACE_MODE_READ_FSCREDS check; see ptrace(2).

              The format of the file is:

                  address           perms offset  dev   inode       pathname
                  00400000-00452000 r-xp 00000000 08:02 173521      /usr/bin/dbus-daemon
                  00651000-00652000 r--p 00051000 08:02 173521      /usr/bin/dbus-daemon
                  00652000-00655000 rw-p 00052000 08:02 173521      /usr/bin/dbus-daemon
                  00e03000-00e24000 rw-p 00000000 00:00 0           [heap]
                  00e24000-011f7000 rw-p 00000000 00:00 0           [heap]
                  ...
                  35b1800000-35b1820000 r-xp 00000000 08:02 135522  /usr/lib64/ld-2.15.so
                  35b1a1f000-35b1a20000 r--p 0001f000 08:02 135522  /usr/lib64/ld-2.15.so
                  35b1a20000-35b1a21000 rw-p 00020000 08:02 135522  /usr/lib64/ld-2.15.so
                  35b1a21000-35b1a22000 rw-p 00000000 00:00 0
                  35b1c00000-35b1dac000 r-xp 00000000 08:02 135870  /usr/lib64/libc-2.15.so
                  35b1dac000-35b1fac000 ---p 001ac000 08:02 135870  /usr/lib64/libc-2.15.so
                  35b1fac000-35b1fb0000 r--p 001ac000 08:02 135870  /usr/lib64/libc-2.15.so
                  35b1fb0000-35b1fb2000 rw-p 001b0000 08:02 135870  /usr/lib64/libc-2.15.so
                  ...
                  f2c6ff8c000-7f2c7078c000 rw-p 00000000 00:00 0    [stack:986]
                  ...
                  7fffb2c0d000-7fffb2c2e000 rw-p 00000000 00:00 0   [stack]
                  7fffb2d48000-7fffb2d49000 r-xp 00000000 00:00 0   [vdso]

              The address field is the address space in the process  that  the
              mapping occupies.  The perms field is a set of permissions:

                  r = read
                  w = write
                  x = execute
                  s = shared
                  p = private (copy on write)

              The  offset  field  is the offset into the file/whatever; dev is
              the device (major:minor); inode is the inode on that device.   0
              indicates that no inode is associated with the memory region, as
              would be the case with BSS (uninitialized data).

              The pathname field will usually be the file that is backing  the
              mapping.  For ELF files, you can easily coordinate with the off-
              set field by looking at the Offset  field  in  the  ELF  program
              headers (readelf -l).

              There are additional helpful pseudo-paths:

              [stack]
                     The  initial  process's (also known as the main thread's)
                     stack.

              [stack:tid] (from Linux 3.4 to Linux 4.4)
                     A thread's stack (where the tid is a thread ID).  It cor-
                     responds to the /proc/pid/task/tid/ path.  This field was
                     removed in Linux 4.5, since  providing  this  information
                     for a process with large numbers of threads is expensive.

              [vdso] The   virtual  dynamically  linked  shared  object.   See
                     vdso(7).

              [heap] The process's heap.

              [anon:name] (since Linux 5.17)
                     A named private anonymous  mapping.   Set  with  prctl(2)
                     PR_SET_VMA_ANON_NAME.

              [anon_shmem:name] (since Linux 6.2)
                     A  named  shared  anonymous  mapping.   Set with prctl(2)
                     PR_SET_VMA_ANON_NAME.

              If the pathname field is blank, this is an anonymous mapping  as
              obtained  via  mmap(2).  There is no easy way to coordinate this
              back to a process's source, short of running it through  gdb(1),
              strace(1), or similar.

              pathname is shown unescaped except for newline characters, which
              are replaced with an octal escape sequence.  As a result, it  is
              not  possible  to  determine  whether the original pathname con-
              tained a newline character or the  literal  \012  character  se-
              quence.

              If the mapping is file-backed and the file has been deleted, the
              string " (deleted)" is appended to the pathname.  Note that this
              is ambiguous too.

              Under Linux 2.0, there is no field giving pathname.

       /proc/pid/mem
              This  file can be used to access the pages of a process's memory
              through open(2), read(2), and lseek(2).

              Permission to access this file is governed by  a  ptrace  access
              mode PTRACE_MODE_ATTACH_FSCREDS check; see ptrace(2).

       /proc/pid/mountinfo (since Linux 2.6.26)
              This  file  contains  information  about mounts in the process's
              mount namespace (see mount_namespaces(7)).  It supplies  various
              information  (e.g.,  propagation  state,  root of mount for bind
              mounts, identifier for each mount and its parent) that is  miss-
              ing  from  the  (older) /proc/pid/mounts file, and fixes various
              other problems with that file (e.g.,  nonextensibility,  failure
              to distinguish per-mount versus per-superblock options).

              The file contains lines of the form:

              36 35 98:0 /mnt1 /mnt2 rw,noatime master:1 - ext3 /dev/root rw,errors=continue
              (1)(2)(3)   (4)   (5)      (6)      (7)   (8) (9)   (10)         (11)

              The  numbers  in parentheses are labels for the descriptions be-
              low:

              (1)  mount ID: a unique ID for the mount (may  be  reused  after
                   umount(2)).

              (2)  parent  ID:  the ID of the parent mount (or of self for the
                   root of this mount namespace's mount tree).

                   If a new mount is stacked on top  of  a  previous  existing
                   mount  (so that it hides the existing mount) at pathname P,
                   then the parent of the new mount is the previous  mount  at
                   that  location.   Thus,  when  looking  at  all  the mounts
                   stacked at a particular location, the top-most mount is the
                   one  that  is not the parent of any other mount at the same
                   location.  (Note, however, that this top-most mount will be
                   accessible  only if the longest path subprefix of P that is
                   a mount point is not itself hidden by a stacked mount.)

                   If the parent mount lies outside the process's root  direc-
                   tory (see chroot(2)), the ID shown here won't have a corre-
                   sponding record in  mountinfo  whose  mount  ID  (field  1)
                   matches  this parent mount ID (because mounts that lie out-
                   side  the  process's  root  directory  are  not  shown   in
                   mountinfo).  As a special case of this point, the process's
                   root mount may have  a  parent  mount  (for  the  initramfs
                   filesystem) that lies outside the process's root directory,
                   and an entry for that mount will not appear in mountinfo.

              (3)  major:minor: the value of st_dev for files on this filesys-
                   tem (see stat(2)).

              (4)  root: the pathname of the directory in the filesystem which
                   forms the root of this mount.

              (5)  mount point: the pathname of the mount  point  relative  to
                   the process's root directory.

              (6)  mount options: per-mount options (see mount(2)).

              (7)  optional   fields:   zero   or  more  fields  of  the  form
                   "tag[:value]"; see below.

              (8)  separator: the end of the optional fields is  marked  by  a
                   single hyphen.

              (9)  filesystem   type:   the   filesystem   type  in  the  form
                   "type[.subtype]".

              (10) mount source: filesystem-specific information or "none".

              (11) super options: per-superblock options (see mount(2)).

              Currently, the possible  optional  fields  are  shared,  master,
              propagate_from,  and  unbindable.  See mount_namespaces(7) for a
              description of these fields.  Parsers should ignore all unrecog-
              nized optional fields.

              For   more  information  on  mount  propagation  see  Documenta-
              tion/filesystems/sharedsubtree.rst  (or   Documentation/filesys-
              tems/sharedsubtree.txt  before  Linux  5.8)  in the Linux kernel
              source tree.

       /proc/pid/mounts (since Linux 2.4.19)
              This file lists all the filesystems  currently  mounted  in  the
              process's mount namespace (see mount_namespaces(7)).  The format
              of this file is documented in fstab(5).

              Since Linux 2.6.15, this file is  pollable:  after  opening  the
              file  for  reading,  a  change  in this file (i.e., a filesystem
              mount or unmount) causes select(2) to mark the  file  descriptor
              as   having   an   exceptional   condition,   and   poll(2)  and
              epoll_wait(2) mark the file as having a  priority  event  (POLL-
              PRI).  (Before Linux 2.6.30, a change in this file was indicated
              by the file descriptor being marked as readable  for  select(2),
              and  being  marked  as having an error condition for poll(2) and
              epoll_wait(2).)

       /proc/pid/mountstats (since Linux 2.6.17)
              This file exports information (statistics, configuration  infor-
              mation)  about  the mounts in the process's mount namespace (see
              mount_namespaces(7)).  Lines in this file have the form:

                  device /dev/sda7 mounted on /home with fstype ext3 [stats]
                  (       1      )            ( 2 )             (3 ) (  4  )

              The fields in each line are:

              (1)  The name of the mounted device (or "nodevice" if  there  is
                   no corresponding device).

              (2)  The mount point within the filesystem tree.

              (3)  The filesystem type.

              (4)  Optional  statistics  and  configuration information.  Cur-
                   rently (as at Linux 2.6.26), only  NFS  filesystems  export
                   information via this field.

              This file is readable only by the owner of the process.

       /proc/pid/net (since Linux 2.6.25)
              See the description of /proc/net.

       /proc/pid/ns/ (since Linux 3.0)
              This  is  a subdirectory containing one entry for each namespace
              that supports being manipulated by setns(2).  For more  informa-
              tion, see namespaces(7).

       /proc/pid/numa_maps (since Linux 2.6.14)
              See numa(7).

       /proc/pid/oom_adj (since Linux 2.6.11)
              This  file  can be used to adjust the score used to select which
              process should be killed in an  out-of-memory  (OOM)  situation.
              The  kernel  uses  this  value  for a bit-shift operation of the
              process's oom_score value: valid values are in the range -16  to
              +15,  plus the special value -17, which disables OOM-killing al-
              together for this process.  A positive score increases the like-
              lihood  of  this process being killed by the OOM-killer; a nega-
              tive score decreases the likelihood.

              The default value for this file is 0; a new process inherits its
              parent's   oom_adj   setting.   A  process  must  be  privileged
              (CAP_SYS_RESOURCE) to update this file.

              Since Linux 2.6.36, use of this file is deprecated in  favor  of
              /proc/pid/oom_score_adj.

       /proc/pid/oom_score (since Linux 2.6.11)
              This  file  displays  the current score that the kernel gives to
              this process for the purpose of selecting a process for the OOM-
              killer.  A higher score means that the process is more likely to
              be selected by the OOM-killer.  The basis for this score is  the
              amount  of memory used by the process, with increases (+) or de-
              creases (-) for factors including:

              •  whether the process is privileged (-).

              Before Linux 2.6.36 the following factors were also used in  the
              calculation of oom_score:

              •  whether  the  process creates a lot of children using fork(2)
                 (+);

              •  whether the process has been running a long time, or has used
                 a lot of CPU time (-);

              •  whether the process has a low nice value (i.e., > 0) (+); and

              •  whether the process is making direct hardware access (-).

              The  oom_score  also  reflects  the  adjustment specified by the
              oom_score_adj or oom_adj setting for the process.

       /proc/pid/oom_score_adj (since Linux 2.6.36)
              This file can be used to adjust the badness  heuristic  used  to
              select which process gets killed in out-of-memory conditions.

              The  badness  heuristic  assigns  a value to each candidate task
              ranging from 0 (never kill) to 1000 (always kill)  to  determine
              which  process  is targeted.  The units are roughly a proportion
              along that range of allowed  memory  the  process  may  allocate
              from, based on an estimation of its current memory and swap use.
              For example, if a task is using all allowed memory, its  badness
              score  will be 1000.  If it is using half of its allowed memory,
              its score will be 500.

              There is an additional factor included  in  the  badness  score:
              root processes are given 3% extra memory over other tasks.

              The  amount  of "allowed" memory depends on the context in which
              the OOM-killer was called.  If it is due to the memory  assigned
              to  the  allocating  task's  cpuset being exhausted, the allowed
              memory represents the set of mems assigned to that  cpuset  (see
              cpuset(7)).   If  it  is  due to a mempolicy's node(s) being ex-
              hausted, the allowed memory  represents  the  set  of  mempolicy
              nodes.   If  it  is  due to a memory limit (or swap limit) being
              reached, the allowed memory is that configured limit.   Finally,
              if  it  is due to the entire system being out of memory, the al-
              lowed memory represents all allocatable resources.

              The value of oom_score_adj is added to the badness score  before
              it  is  used to determine which task to kill.  Acceptable values
              range    from     -1000     (OOM_SCORE_ADJ_MIN)     to     +1000
              (OOM_SCORE_ADJ_MAX).   This  allows  user  space  to control the
              preference for OOM-killing, ranging  from  always  preferring  a
              certain  task  or completely disabling it from OOM-killing.  The
              lowest possible value, -1000, is equivalent  to  disabling  OOM-
              killing  entirely  for  that task, since it will always report a
              badness score of 0.

              Consequently, it is very simple for user  space  to  define  the
              amount  of  memory  to  consider  for  each  task.   Setting  an
              oom_score_adj value of +500, for example, is roughly  equivalent
              to  allowing  the  remainder  of  tasks sharing the same system,
              cpuset, mempolicy, or memory  controller  resources  to  use  at
              least  50%  more  memory.   A  value of -500, on the other hand,
              would be roughly equivalent to discounting 50% of the task's al-
              lowed memory from being considered as scoring against the task.

              For    backward    compatibility    with    previous    kernels,
              /proc/pid/oom_adj can still be used to tune the  badness  score.
              Its value is scaled linearly with oom_score_adj.

              Writing  to  /proc/pid/oom_score_adj  or  /proc/pid/oom_adj will
              change the other with its scaled value.

              The choom(1) program provides a command-line interface  for  ad-
              justing  the oom_score_adj value of a running process or a newly
              executed command.

       /proc/pid/pagemap (since Linux 2.6.25)
              This file shows the mapping of each  of  the  process's  virtual
              pages  into  physical page frames or swap area.  It contains one
              64-bit value for each virtual page, with the bits  set  as  fol-
              lows:

              63     If set, the page is present in RAM.

              62     If set, the page is in swap space

              61 (since Linux 3.5)
                     The  page  is  a  file-mapped  page or a shared anonymous
                     page.

              60–58 (since Linux 3.11)
                     Zero

              57 (since Linux 5.14)
                     If  set,  the  page  is  write-protected  through   user-
                     faultfd(2).

              56 (since Linux 4.2)
                     The page is exclusively mapped.

              55 (since Linux 3.11)
                     PTE  is soft-dirty (see the kernel source file Documenta-
                     tion/admin-guide/mm/soft-dirty.rst).

              54–0   If the page is present in RAM (bit 63), then  these  bits
                     provide the page frame number, which can be used to index
                     /proc/kpageflags and /proc/kpagecount.  If  the  page  is
                     present  in  swap  (bit  62), then bits 4–0 give the swap
                     type, and bits 54–5 encode the swap offset.

              Before Linux 3.11, bits 60–55 were used to encode the base-2 log
              of the page size.

              To  employ  /proc/pid/pagemap efficiently, use /proc/pid/maps to
              determine which areas of memory are actually mapped and seek  to
              skip over unmapped regions.

              The   /proc/pid/pagemap   file  is  present  only  if  the  CON-
              FIG_PROC_PAGE_MONITOR kernel configuration option is enabled.

              Permission to access this file is governed by  a  ptrace  access
              mode PTRACE_MODE_READ_FSCREDS check; see ptrace(2).

       /proc/pid/personality (since Linux 2.6.28)
              This  read-only  file exposes the process's execution domain, as
              set by personality(2).  The value is  displayed  in  hexadecimal
              notation.

              Permission  to  access  this file is governed by a ptrace access
              mode PTRACE_MODE_ATTACH_FSCREDS check; see ptrace(2).

       /proc/pid/root
              UNIX and Linux support the idea of a  per-process  root  of  the
              filesystem,  set  by  the chroot(2) system call.  This file is a
              symbolic link that points to the process's root  directory,  and
              behaves in the same way as exe, and fd/*.

              Note  however  that this file is not merely a symbolic link.  It
              provides the same view of the filesystem  (including  namespaces
              and  the  set  of per-process mounts) as the process itself.  An
              example illustrates this point.  In one  terminal,  we  start  a
              shell  in  new  user  and mount namespaces, and in that shell we
              create some new mounts:

                  $ PS1='sh1# ' unshare -Urnm
                  sh1# mount -t tmpfs tmpfs /etc  # Mount empty tmpfs at /etc
                  sh1# mount --bind /usr /dev     # Mount /usr at /dev
                  sh1# echo $$
                  27123

              In a second terminal window, in the initial mount namespace,  we
              look  at the contents of the corresponding mounts in the initial
              and new namespaces:

                  $ PS1='sh2# ' sudo sh
                  sh2# ls /etc | wc -l                  # In initial NS
                  309
                  sh2# ls /proc/27123/root/etc | wc -l  # /etc in other NS
                  0                                     # The empty tmpfs dir
                  sh2# ls /dev | wc -l                  # In initial NS
                  205
                  sh2# ls /proc/27123/root/dev | wc -l  # /dev in other NS
                  11                                    # Actually bind
                                                        # mounted to /usr
                  sh2# ls /usr | wc -l                  # /usr in initial NS
                  11

              In a multithreaded process, the contents of  the  /proc/pid/root
              symbolic  link  are not available if the main thread has already
              terminated (typically by calling pthread_exit(3)).

              Permission to dereference or read  (readlink(2))  this  symbolic
              link  is  governed  by a ptrace access mode PTRACE_MODE_READ_FS-
              CREDS check; see ptrace(2).

       /proc/pid/projid_map (since Linux 3.7)
              See user_namespaces(7).

       /proc/pid/seccomp (Linux 2.6.12 to Linux 2.6.22)
              This file can be used to read and change  the  process's  secure
              computing  (seccomp)  mode  setting.  It contains the value 0 if
              the process is not in seccomp mode, and 1 if the process  is  in
              strict  seccomp  mode  (see seccomp(2)).  Writing 1 to this file
              places the process irreversibly in strict seccomp  mode.   (Fur-
              ther attempts to write to the file fail with the EPERM error.)

              In  Linux  2.6.23,  this  file  went away, to be replaced by the
              prctl(2) PR_GET_SECCOMP and PR_SET_SECCOMP operations (and later
              by seccomp(2) and the Seccomp field in /proc/pid/status).

       /proc/pid/setgroups (since Linux 3.19)
              See user_namespaces(7).

       /proc/pid/smaps (since Linux 2.6.14)
              This  file  shows  memory  consumption for each of the process's
              mappings.  (The pmap(1) command displays similar information, in
              a  form that may be easier for parsing.)  For each mapping there
              is a series of lines such as the following:

                  00400000-0048a000 r-xp 00000000 fd:03 960637       /bin/bash
                  Size:                552 kB
                  Rss:                 460 kB
                  Pss:                 100 kB
                  Shared_Clean:        452 kB
                  Shared_Dirty:          0 kB
                  Private_Clean:         8 kB
                  Private_Dirty:         0 kB
                  Referenced:          460 kB
                  Anonymous:             0 kB
                  AnonHugePages:         0 kB
                  ShmemHugePages:        0 kB
                  ShmemPmdMapped:        0 kB
                  Swap:                  0 kB
                  KernelPageSize:        4 kB
                  MMUPageSize:           4 kB
                  Locked:                0 kB
                  ProtectionKey:         0
                  VmFlags: rd ex mr mw me dw

              The first of these lines shows the same information as  is  dis-
              played  for  the mapping in /proc/pid/maps.  The following lines
              show the size of the mapping, the amount of the mapping that  is
              currently  resident  in  RAM ("Rss"), the process's proportional
              share of this mapping ("Pss"), the number  of  clean  and  dirty
              shared  pages  in the mapping, and the number of clean and dirty
              private pages in the mapping.  "Referenced" indicates the amount
              of  memory  currently marked as referenced or accessed.  "Anony-
              mous" shows the amount of memory that does  not  belong  to  any
              file.   "Swap"  shows how much would-be-anonymous memory is also
              used, but out on swap.

              The "KernelPageSize" line (available since Linux 2.6.29) is  the
              page  size  used  by the kernel to back the virtual memory area.
              This matches the size used by the MMU in the majority of  cases.
              However,  one  counter-example occurs on PPC64 kernels whereby a
              kernel using 64 kB as a base page size may still use 4 kB  pages
              for  the  MMU  on  older processors.  To distinguish the two at-
              tributes, the "MMUPageSize" line  (also  available  since  Linux
              2.6.29) reports the page size used by the MMU.

              The  "Locked"  indicates whether the mapping is locked in memory
              or not.

              The "ProtectionKey" line (available  since  Linux  4.9,  on  x86
              only)  contains the memory protection key (see pkeys(7)) associ-
              ated with the virtual memory area.  This entry is  present  only
              if the kernel was built with the CONFIG_X86_INTEL_MEMORY_PROTEC-
              TION_KEYS configuration option (since Linux 4.6).

              The "VmFlags" line (available since Linux  3.8)  represents  the
              kernel  flags  associated  with the virtual memory area, encoded
              using the following two-letter codes:

                     rd   -   readable
                     wr   -   writable
                     ex   -   executable
                     sh   -   shared
                     mr   -   may read
                     mw   -   may write
                     me   -   may execute
                     ms   -   may share
                     gd   -   stack segment grows down
                     pf   -   pure PFN range
                     dw   -   disabled write to the mapped file
                     lo   -   pages are locked in memory
                     io   -   memory mapped I/O area
                     sr   -   sequential read advise provided
                     rr   -   random read advise provided
                     dc   -   do not copy area on fork
                     de   -   do not expand area on remapping
                     ac   -   area is accountable
                     nr   -   swap space is not reserved for the area
                     ht   -   area uses huge tlb pages
                     sf   -   perform synchronous page faults (since Linux 4.15)
                     nl   -   non-linear mapping (removed in Linux 4.0)
                     ar   -   architecture specific flag
                     wf   -   wipe on fork (since Linux 4.14)
                     dd   -   do not include area into core dump
                     sd   -   soft-dirty flag (since Linux 3.13)
                     mm   -   mixed map area
                     hg   -   huge page advise flag
                     nh   -   no-huge page advise flag
                     mg   -   mergeable advise flag
                     um   -   userfaultfd missing pages tracking (since Linux 4.3)
                     uw   -   userfaultfd wprotect pages tracking (since Linux 4.3)

              The  /proc/pid/smaps  file  is  present   only   if   the   CON-
              FIG_PROC_PAGE_MONITOR kernel configuration option is enabled.

       /proc/pid/stack (since Linux 2.6.29)
              This  file  provides  a  symbolic trace of the function calls in
              this process's kernel stack.  This file is provided only if  the
              kernel  was  built  with the CONFIG_STACKTRACE configuration op-
              tion.

              Permission to access this file is governed by  a  ptrace  access
              mode PTRACE_MODE_ATTACH_FSCREDS check; see ptrace(2).

       /proc/pid/stat
              Status  information  about  the process.  This is used by ps(1).
              It is defined in the kernel source file fs/proc/array.c.

              The fields, in order, with their proper scanf(3)  format  speci-
              fiers, are listed below.  Whether or not certain of these fields
              display valid information is governed by a  ptrace  access  mode
              PTRACE_MODE_READ_FSCREDS  |  PTRACE_MODE_NOAUDIT check (refer to
              ptrace(2)).  If the check denies access, then the field value is
              displayed  as  0.   The  affected  fields are indicated with the
              marking [PT].

              (1) pid  %d
                     The process ID.

              (2) comm  %s
                     The filename of the executable, in parentheses.   Strings
                     longer  than TASK_COMM_LEN (16) characters (including the
                     terminating null byte) are silently truncated.   This  is
                     visible whether or not the executable is swapped out.

              (3) state  %c
                     One  of  the  following  characters,  indicating  process
                     state:

                     R      Running

                     S      Sleeping in an interruptible wait

                     D      Waiting in uninterruptible disk sleep

                     Z      Zombie

                     T      Stopped (on a signal)  or  (before  Linux  2.6.33)
                            trace stopped

                     t      Tracing stop (Linux 2.6.33 onward)

                     W      Paging (only before Linux 2.6.0)

                     X      Dead (from Linux 2.6.0 onward)

                     x      Dead (Linux 2.6.33 to 3.13 only)

                     K      Wakekill (Linux 2.6.33 to 3.13 only)

                     W      Waking (Linux 2.6.33 to 3.13 only)

                     P      Parked (Linux 3.9 to 3.13 only)

                     I      Idle (Linux 4.14 onward)

              (4) ppid  %d
                     The PID of the parent of this process.

              (5) pgrp  %d
                     The process group ID of the process.

              (6) session  %d
                     The session ID of the process.

              (7) tty_nr  %d
                     The  controlling terminal of the process.  (The minor de-
                     vice number is contained in the combination of bits 31 to
                     20  and  7 to 0; the major device number is in bits 15 to
                     8.)

              (8) tpgid  %d
                     The ID of the foreground process group of the controlling
                     terminal of the process.

              (9) flags  %u
                     The  kernel flags word of the process.  For bit meanings,
                     see the PF_* defines in the Linux kernel source file  in-
                     clude/linux/sched.h.   Details  depend on the kernel ver-
                     sion.

                     The format for this field was %lu before Linux 2.6.

              (10) minflt  %lu
                     The number of minor faults the  process  has  made  which
                     have not required loading a memory page from disk.

              (11) cminflt  %lu
                     The  number of minor faults that the process's waited-for
                     children have made.

              (12) majflt  %lu
                     The number of major faults the  process  has  made  which
                     have required loading a memory page from disk.

              (13) cmajflt  %lu
                     The  number of major faults that the process's waited-for
                     children have made.

              (14) utime  %lu
                     Amount of time that this process has  been  scheduled  in
                     user   mode,   measured   in   clock   ticks  (divide  by
                     sysconf(_SC_CLK_TCK)).    This   includes   guest   time,
                     guest_time (time spent running a virtual CPU, see below),
                     so that applications that are not aware of the guest time
                     field do not lose that time from their calculations.

              (15) stime  %lu
                     Amount  of  time  that this process has been scheduled in
                     kernel  mode,  measured  in  clock   ticks   (divide   by
                     sysconf(_SC_CLK_TCK)).

              (16) cutime  %ld
                     Amount  of  time  that this process's waited-for children
                     have been scheduled in user mode, measured in clock ticks
                     (divide  by  sysconf(_SC_CLK_TCK)).  (See also times(2).)
                     This includes guest time, cguest_time (time spent running
                     a virtual CPU, see below).

              (17) cstime  %ld
                     Amount  of  time  that this process's waited-for children
                     have been scheduled in kernel  mode,  measured  in  clock
                     ticks (divide by sysconf(_SC_CLK_TCK)).

              (18) priority  %ld
                     (Explanation for Linux 2.6) For processes running a real-
                     time scheduling policy (policy below; see sched_setsched-
                     uler(2)),  this is the negated scheduling priority, minus
                     one; that is, a number in the range -2  to  -100,  corre-
                     sponding  to real-time priorities 1 to 99.  For processes
                     running under a non-real-time scheduling policy, this  is
                     the raw nice value (setpriority(2)) as represented in the
                     kernel.  The kernel stores nice values as numbers in  the
                     range  0  (high)  to 39 (low), corresponding to the user-
                     visible nice range of -20 to 19.

                     Before Linux 2.6, this was a scaled value  based  on  the
                     scheduler weighting given to this process.

              (19) nice  %ld
                     The nice value (see setpriority(2)), a value in the range
                     19 (low priority) to -20 (high priority).

              (20) num_threads  %ld
                     Number of threads in this process (since Linux 2.6).  Be-
                     fore  Linux  2.6,  this  field  was  hard coded to 0 as a
                     placeholder for an earlier removed field.

              (21) itrealvalue  %ld
                     The time in jiffies before the next SIGALRM  is  sent  to
                     the  process  due  to  an  interval  timer.   Since Linux
                     2.6.17, this field is no longer maintained, and  is  hard
                     coded as 0.

              (22) starttime  %llu
                     The  time  the process started after system boot.  Before
                     Linux 2.6, this value was expressed  in  jiffies.   Since
                     Linux  2.6, the value is expressed in clock ticks (divide
                     by sysconf(_SC_CLK_TCK)).

                     The format for this field was %lu before Linux 2.6.

              (23) vsize  %lu
                     Virtual memory size in bytes.

              (24) rss  %ld
                     Resident Set Size: number of pages  the  process  has  in
                     real  memory.   This is just the pages which count toward
                     text, data, or stack space.  This does not include  pages
                     which  have  not  been  demand-loaded  in,  or  which are
                     swapped   out.    This   value   is    inaccurate;    see
                     /proc/pid/statm below.

              (25) rsslim  %lu
                     Current  soft  limit  in bytes on the rss of the process;
                     see the description of RLIMIT_RSS in getrlimit(2).

              (26) startcode  %lu  [PT]
                     The address above which program text can run.

              (27) endcode  %lu  [PT]
                     The address below which program text can run.

              (28) startstack  %lu  [PT]
                     The address of the start (i.e., bottom) of the stack.

              (29) kstkesp  %lu  [PT]
                     The current value of ESP (stack pointer), as found in the
                     kernel stack page for the process.

              (30) kstkeip  %lu  [PT]
                     The current EIP (instruction pointer).

              (31) signal  %lu
                     The  bitmap  of  pending  signals, displayed as a decimal
                     number.  Obsolete, because it does not  provide  informa-
                     tion on real-time signals; use /proc/pid/status instead.

              (32) blocked  %lu
                     The  bitmap  of  blocked  signals, displayed as a decimal
                     number.  Obsolete, because it does not  provide  informa-
                     tion on real-time signals; use /proc/pid/status instead.

              (33) sigignore  %lu
                     The  bitmap  of  ignored  signals, displayed as a decimal
                     number.  Obsolete, because it does not  provide  informa-
                     tion on real-time signals; use /proc/pid/status instead.

              (34) sigcatch  %lu
                     The bitmap of caught signals, displayed as a decimal num-
                     ber.  Obsolete, because it does not  provide  information
                     on real-time signals; use /proc/pid/status instead.

              (35) wchan  %lu  [PT]
                     This  is  the  "channel" in which the process is waiting.
                     It is the address of a location in the kernel  where  the
                     process is sleeping.  The corresponding symbolic name can
                     be found in /proc/pid/wchan.

              (36) nswap  %lu
                     Number of pages swapped (not maintained).

              (37) cnswap  %lu
                     Cumulative nswap for child processes (not maintained).

              (38) exit_signal  %d  (since Linux 2.1.22)
                     Signal to be sent to parent when we die.

              (39) processor  %d  (since Linux 2.2.8)
                     CPU number last executed on.

              (40) rt_priority  %u  (since Linux 2.5.19)
                     Real-time scheduling priority, a number in the range 1 to
                     99  for  processes scheduled under a real-time policy, or
                     0,  for  non-real-time  processes  (see   sched_setsched-
                     uler(2)).

              (41) policy  %u  (since Linux 2.5.19)
                     Scheduling  policy  (see  sched_setscheduler(2)).  Decode
                     using the SCHED_* constants in linux/sched.h.

                     The format for this field was %lu before Linux 2.6.22.

              (42) delayacct_blkio_ticks  %llu  (since Linux 2.6.18)
                     Aggregated block I/O  delays,  measured  in  clock  ticks
                     (centiseconds).

              (43) guest_time  %lu  (since Linux 2.6.24)
                     Guest  time  of the process (time spent running a virtual
                     CPU for a guest  operating  system),  measured  in  clock
                     ticks (divide by sysconf(_SC_CLK_TCK)).

              (44) cguest_time  %ld  (since Linux 2.6.24)
                     Guest  time  of the process's children, measured in clock
                     ticks (divide by sysconf(_SC_CLK_TCK)).

              (45) start_data  %lu  (since Linux 3.3)  [PT]
                     Address above which program initialized and uninitialized
                     (BSS) data are placed.

              (46) end_data  %lu  (since Linux 3.3)  [PT]
                     Address below which program initialized and uninitialized
                     (BSS) data are placed.

              (47) start_brk  %lu  (since Linux 3.3)  [PT]
                     Address above which program heap  can  be  expanded  with
                     brk(2).

              (48) arg_start  %lu  (since Linux 3.5)  [PT]
                     Address above which program command-line arguments (argv)
                     are placed.

              (49) arg_end  %lu  (since Linux 3.5)  [PT]
                     Address below program command-line arguments  (argv)  are
                     placed.

              (50) env_start  %lu  (since Linux 3.5)  [PT]
                     Address above which program environment is placed.

              (51) env_end  %lu  (since Linux 3.5)  [PT]
                     Address below which program environment is placed.

              (52) exit_code  %d  (since Linux 3.5)  [PT]
                     The  thread's  exit  status in the form reported by wait-
                     pid(2).

       /proc/pid/statm
              Provides information about memory usage, measured in pages.  The
              columns are:

                  size       (1) total program size
                             (same as VmSize in /proc/pid/status)
                  resident   (2) resident set size
                             (inaccurate; same as VmRSS in /proc/pid/status)
                  shared     (3) number of resident shared pages
                             (i.e., backed by a file)
                             (inaccurate; same as RssFile+RssShmem in
                             /proc/pid/status)
                  text       (4) text (code)
                  lib        (5) library (unused since Linux 2.6; always 0)
                  data       (6) data + stack
                  dt         (7) dirty pages (unused since Linux 2.6; always 0)

              Some of these values are inaccurate because of a kernel-internal
              scalability optimization.  If accurate values are required,  use
              /proc/pid/smaps  or  /proc/pid/smaps_rollup  instead,  which are
              much slower but provide accurate, detailed information.

       /proc/pid/status
              Provides  much  of  the  information   in   /proc/pid/stat   and
              /proc/pid/statm  in  a format that's easier for humans to parse.
              Here's an example:

                  $ cat /proc/$$/status
                  Name:   bash
                  Umask:  0022
                  State:  S (sleeping)
                  Tgid:   17248
                  Ngid:   0
                  Pid:    17248
                  PPid:   17200
                  TracerPid:      0
                  Uid:    1000    1000    1000    1000
                  Gid:    100     100     100     100
                  FDSize: 256
                  Groups: 16 33 100
                  NStgid: 17248
                  NSpid:  17248
                  NSpgid: 17248
                  NSsid:  17200
                  VmPeak:                                                         131168 kB
                  VmSize:                                                         131168 kB
                  VmLck:                                                               0 kB
                  VmPin:                                                               0 kB
                  VmHWM:                                                           13484 kB
                  VmRSS:                                                           13484 kB
                  RssAnon:                                                         10264 kB
                  RssFile:                                                          3220 kB
                  RssShmem:                                                            0 kB
                  VmData:                                                          10332 kB
                  VmStk:                                                             136 kB
                  VmExe:                                                             992 kB
                  VmLib:                                                            2104 kB
                  VmPTE:                                                              76 kB
                  VmPMD:                                                              12 kB
                  VmSwap:                                                              0 kB
                  HugetlbPages:          0 kB                                   # 4.4
                  CoreDumping:                                                  0                       # 4.15
                  Threads:        1
                  SigQ:   0/3067
                  SigPnd: 0000000000000000
                  ShdPnd: 0000000000000000
                  SigBlk: 0000000000010000
                  SigIgn: 0000000000384004
                  SigCgt: 000000004b813efb
                  CapInh: 0000000000000000
                  CapPrm: 0000000000000000
                  CapEff: 0000000000000000
                  CapBnd: ffffffffffffffff
                  CapAmb:                                                       0000000000000000
                  NoNewPrivs:     0
                  Seccomp:        0
                  Speculation_Store_Bypass:       vulnerable
                  Cpus_allowed:   00000001
                  Cpus_allowed_list:      0
                  Mems_allowed:   1
                  Mems_allowed_list:      0
                  voluntary_ctxt_switches:        150
                  nonvoluntary_ctxt_switches:     545

              The fields are as follows:

              Name   Command  run  by  this  process.   Strings  longer   than
                     TASK_COMM_LEN  (16) characters (including the terminating
                     null byte) are silently truncated.

              Umask  Process umask, expressed in octal with  a  leading  zero;
                     see umask(2).  (Since Linux 4.7.)

              State  Current  state  of the process.  One of "R (running)", "S
                     (sleeping)", "D (disk sleep)", "T (stopped)", "t (tracing
                     stop)", "Z (zombie)", or "X (dead)".

              Tgid   Thread group ID (i.e., Process ID).

              Ngid   NUMA group ID (0 if none; since Linux 3.13).

              Pid    Thread ID (see gettid(2)).

              PPid   PID of parent process.

              TracerPid
                     PID  of  process  tracing  this  process  (0 if not being
                     traced).

              Uid, Gid
                     Real, effective, saved set, and filesystem UIDs (GIDs).

              FDSize Number of file descriptor slots currently allocated.

              Groups Supplementary group list.

              NStgid Thread group ID (i.e., PID) in each of the PID namespaces
                     of  which  pid is a member.  The leftmost entry shows the
                     value with respect to the PID namespace  of  the  process
                     that  mounted  this  procfs  (or  the  root  namespace if
                     mounted by the kernel), followed by the value in  succes-
                     sively nested inner namespaces.  (Since Linux 4.1.)

              NSpid  Thread ID in each of the PID namespaces of which pid is a
                     member.  The fields are ordered as  for  NStgid.   (Since
                     Linux 4.1.)

              NSpgid Process  group  ID in each of the PID namespaces of which
                     pid is a member.  The fields are ordered as  for  NStgid.
                     (Since Linux 4.1.)

              NSsid  descendant  namespace  session ID hierarchy Session ID in
                     each of the PID namespaces of which pid is a member.  The
                     fields are ordered as for NStgid.  (Since Linux 4.1.)

              VmPeak Peak virtual memory size.

              VmSize Virtual memory size.

              VmLck  Locked memory size (see mlock(2)).

              VmPin  Pinned  memory  size  (since Linux 3.2).  These are pages
                     that can't be moved because something needs  to  directly
                     access physical memory.

              VmHWM  Peak  resident  set size ("high water mark").  This value
                     is inaccurate; see /proc/pid/statm above.

              VmRSS  Resident set size.  Note that the value here is  the  sum
                     of RssAnon, RssFile, and RssShmem.  This value is inaccu-
                     rate; see /proc/pid/statm above.

              RssAnon
                     Size of resident anonymous memory.   (since  Linux  4.5).
                     This value is inaccurate; see /proc/pid/statm above.

              RssFile
                     Size of resident file mappings.  (since Linux 4.5).  This
                     value is inaccurate; see /proc/pid/statm above.

              RssShmem
                     Size of resident shared memory (includes System V  shared
                     memory, mappings from tmpfs(5), and shared anonymous map-
                     pings).  (since Linux 4.5).

              VmData, VmStk, VmExe
                     Size of data, stack, and text segments.   This  value  is
                     inaccurate; see /proc/pid/statm above.

              VmLib  Shared library code size.

              VmPTE  Page table entries size (since Linux 2.6.10).

              VmPMD  Size of second-level page tables (added in Linux 4.0; re-
                     moved in Linux 4.15).

              VmSwap Swapped-out virtual  memory  size  by  anonymous  private
                     pages;  shmem  swap  usage  is  not included (since Linux
                     2.6.34).  This value is inaccurate;  see  /proc/pid/statm
                     above.

              HugetlbPages
                     Size of hugetlb memory portions (since Linux 4.4).

              CoreDumping
                     Contains  the value 1 if the process is currently dumping
                     core, and 0 if it is not (since Linux 4.15).  This infor-
                     mation  can  be  used  by  a  monitoring process to avoid
                     killing a process that is currently dumping  core,  which
                     could result in a corrupted core dump file.

              Threads
                     Number of threads in process containing this thread.

              SigQ   This  field contains two slash-separated numbers that re-
                     late to queued signals for  the  real  user  ID  of  this
                     process.   The  first of these is the number of currently
                     queued signals for this real user ID, and the  second  is
                     the  resource  limit  on the number of queued signals for
                     this process (see the description of RLIMIT_SIGPENDING in
                     getrlimit(2)).

              SigPnd, ShdPnd
                     Mask  (expressed  in  hexadecimal) of signals pending for
                     thread and for process as a whole  (see  pthreads(7)  and
                     signal(7)).

              SigBlk, SigIgn, SigCgt
                     Masks (expressed in hexadecimal) indicating signals being
                     blocked, ignored, and caught (see signal(7)).

              CapInh, CapPrm, CapEff
                     Masks (expressed in hexadecimal) of capabilities  enabled
                     in  inheritable, permitted, and effective sets (see capa-
                     bilities(7)).

              CapBnd Capability bounding set, expressed in hexadecimal  (since
                     Linux 2.6.26, see capabilities(7)).

              CapAmb Ambient  capability  set, expressed in hexadecimal (since
                     Linux 4.3, see capabilities(7)).

              NoNewPrivs
                     Value of the no_new_privs  bit  (since  Linux  4.10,  see
                     prctl(2)).

              Seccomp
                     Seccomp  mode  of  the process (since Linux 3.8, see sec-
                     comp(2)).  0 means SECCOMP_MODE_DISABLED;  1  means  SEC-
                     COMP_MODE_STRICT;   2  means  SECCOMP_MODE_FILTER.   This
                     field is provided only if the kernel was built  with  the
                     CONFIG_SECCOMP kernel configuration option enabled.

              Speculation_Store_Bypass
                     Speculation  flaw mitigation state (since Linux 4.17, see
                     prctl(2)).

              Cpus_allowed
                     Hexadecimal mask of CPUs on which this  process  may  run
                     (since Linux 2.6.24, see cpuset(7)).

              Cpus_allowed_list
                     Same  as  previous,  but  in  "list  format" (since Linux
                     2.6.26, see cpuset(7)).

              Mems_allowed
                     Mask of memory nodes allowed to this process (since Linux
                     2.6.24, see cpuset(7)).

              Mems_allowed_list
                     Same  as  previous,  but  in  "list  format" (since Linux
                     2.6.26, see cpuset(7)).

              voluntary_ctxt_switches, nonvoluntary_ctxt_switches
                     Number of  voluntary  and  involuntary  context  switches
                     (since Linux 2.6.23).

       /proc/pid/syscall (since Linux 2.6.27)
              This  file exposes the system call number and argument registers
              for the system call currently being  executed  by  the  process,
              followed  by the values of the stack pointer and program counter
              registers.  The values of all six  argument  registers  are  ex-
              posed, although most system calls use fewer registers.

              If  the  process  is blocked, but not in a system call, then the
              file displays -1 in place of the system call number, followed by
              just  the  values  of the stack pointer and program counter.  If
              process is not blocked, then the file contains just  the  string
              "running".

              This file is present only if the kernel was configured with CON-
              FIG_HAVE_ARCH_TRACEHOOK.

              Permission to access this file is governed by  a  ptrace  access
              mode PTRACE_MODE_ATTACH_FSCREDS check; see ptrace(2).

       /proc/pid/task (since Linux 2.6.0)
              This  is  a  directory  that  contains one subdirectory for each
              thread in the process.  The name of each subdirectory is the nu-
              merical thread ID (tid) of the thread (see gettid(2)).

              Within  each  of  these  subdirectories, there is a set of files
              with the same names and contents as under the /proc/pid directo-
              ries.   For  attributes that are shared by all threads, the con-
              tents for each of the files under  the  task/tid  subdirectories
              will  be  the  same  as  in the corresponding file in the parent
              /proc/pid directory (e.g., in a multithreaded  process,  all  of
              the   task/tid/cwd  files  will  have  the  same  value  as  the
              /proc/pid/cwd file in the parent directory,  since  all  of  the
              threads in a process share a working directory).  For attributes
              that are distinct for each thread, the corresponding files under
              task/tid may have different values (e.g., various fields in each
              of the task/tid/status files may be different for each  thread),
              or they might not exist in /proc/pid at all.

              In  a  multithreaded process, the contents of the /proc/pid/task
              directory are not available if the main thread has already  ter-
              minated (typically by calling pthread_exit(3)).

       /proc/pid/task/tid/children (since Linux 3.5)
              A  space-separated list of child tasks of this task.  Each child
              task is represented by its TID.

              This option is intended for use by the checkpoint-restore (CRIU)
              system,  and reliably provides a list of children only if all of
              the child processes are stopped or frozen.   It  does  not  work
              properly  if  children of the target task exit while the file is
              being read!  Exiting children may cause non-exiting children  to
              be  omitted  from the list.  This makes this interface even more
              unreliable than classic PID-based approaches  if  the  inspected
              task and its children aren't frozen, and most code should proba-
              bly not use this interface.

              Until Linux 4.2, the presence of this file was governed  by  the
              CONFIG_CHECKPOINT_RESTORE  kernel  configuration  option.  Since
              Linux 4.2, it is governed by the CONFIG_PROC_CHILDREN option.

       /proc/pid/timers (since Linux 3.10)
              A list of the POSIX timers for  this  process.   Each  timer  is
              listed with a line that starts with the string "ID:".  For exam-
              ple:

                  ID: 1
                  signal: 60/00007fff86e452a8
                  notify: signal/pid.2634
                  ClockID: 0
                  ID: 0
                  signal: 60/00007fff86e452a8
                  notify: signal/pid.2634
                  ClockID: 1

              The lines shown for each timer have the following meanings:

              ID     The ID for this timer.  This is not the same as the timer
                     ID  returned  by  timer_create(2); rather, it is the same
                     kernel-internal ID that is available via  the  si_timerid
                     field of the siginfo_t structure (see sigaction(2)).

              signal This is the signal number that this timer uses to deliver
                     notifications  followed  by  a  slash,   and   then   the
                     sigev_value  value supplied to the signal handler.  Valid
                     only for timers that notify via a signal.

              notify The part before the slash specifies  the  mechanism  that
                     this  timer  uses to deliver notifications, and is one of
                     "thread", "signal", or "none".  Immediately following the
                     slash   is  either  the  string  "tid"  for  timers  with
                     SIGEV_THREAD_ID notification, or "pid"  for  timers  that
                     notify by other mechanisms.  Following the "." is the PID
                     of the process (or the kernel thread ID  of  the  thread)
                     that will be delivered a signal if the timer delivers no-
                     tifications via a signal.

              ClockID
                     This field identifies the clock that the timer  uses  for
                     measuring  time.   For most clocks, this is a number that
                     matches one of the user-space CLOCK_*  constants  exposed
                     via  <time.h>.   CLOCK_PROCESS_CPUTIME_ID  timers display
                     with    a    value    of    -6     in     this     field.
                     CLOCK_THREAD_CPUTIME_ID timers display with a value of -2
                     in this field.

              This file is available only when the kernel was configured  with
              CONFIG_CHECKPOINT_RESTORE.

       /proc/pid/timerslack_ns (since Linux 4.6)
              This file exposes the process's "current" timer slack value, ex-
              pressed in nanoseconds.  The  file  is  writable,  allowing  the
              process's  timer  slack  value to be changed.  Writing 0 to this
              file resets the "current" timer slack  to  the  "default"  timer
              slack  value.   For  further  details,  see  the  discussion  of
              PR_SET_TIMERSLACK in prctl(2).

              Initially, permission to access this  file  was  governed  by  a
              ptrace   access   mode   PTRACE_MODE_ATTACH_FSCREDS  check  (see
              ptrace(2)).  However, this was subsequently deemed too strict  a
              requirement (and had the side effect that requiring a process to
              have the CAP_SYS_PTRACE capability would also allow it  to  view
              and  change  any process's memory).  Therefore, since Linux 4.9,
              only the (weaker) CAP_SYS_NICE capability is required to  access
              this file.

       /proc/pid/uid_map (since Linux 3.5)
              See user_namespaces(7).

       /proc/pid/wchan (since Linux 2.6.0)
              The  symbolic  name  corresponding to the location in the kernel
              where the process is sleeping.

              Permission to access this file is governed by  a  ptrace  access
              mode PTRACE_MODE_READ_FSCREDS check; see ptrace(2).

       /proc/tid
              There   is a numerical subdirectory for each running thread that
              is not a thread group leader (i.e., a thread whose thread ID  is
              not  the  same  as its process ID); the subdirectory is named by
              the thread ID.  Each one of these subdirectories contains  files
              and  subdirectories  exposing  information about the thread with
              the thread ID tid.  The contents of these  directories  are  the
              same as the corresponding /proc/pid/task/tid directories.

              The  /proc/tid  subdirectories  are  not  visible when iterating
              through /proc with getdents(2) (and thus are  not  visible  when
              one  uses  ls(1)  to  view the contents of /proc).  However, the
              pathnames of these directories are visible to (i.e.,  usable  as
              arguments in) system calls that operate on pathnames.

       /proc/apm
              Advanced  power  management version and battery information when
              CONFIG_APM is defined at kernel compilation time.

       /proc/buddyinfo
              This file contains information which is used for diagnosing mem-
              ory fragmentation issues.  Each line starts with the identifica-
              tion of the node and the name of the zone which  together  iden-
              tify  a  memory  region.   This is then followed by the count of
              available chunks of a certain order in  which  these  zones  are
              split.   The  size  in  bytes of a certain order is given by the
              formula:

                  (2^order) * PAGE_SIZE

              The binary buddy allocator  algorithm  inside  the  kernel  will
              split  one  chunk  into two chunks of a smaller order (thus with
              half the size) or combine two contiguous chunks into one  larger
              chunk  of  a higher order (thus with double the size) to satisfy
              allocation requests and to counter  memory  fragmentation.   The
              order matches the column number, when starting to count at zero.

              For example on an x86-64 system:
         Node 0, zone     DMA     1    1    1    0    2    1    1    0    1    1    3
         Node 0, zone   DMA32    65   47    4   81   52   28   13   10    5    1  404
         Node 0, zone  Normal   216   55  189  101   84   38   37   27    5    3  587

              In  this  example,  there is one node containing three zones and
              there are 11 different chunk sizes.  If the page size is 4 kilo-
              bytes,  then  the  first  zone  called  DMA (on x86 the first 16
              megabyte of memory) has 1 chunk of 4 kilobytes (order 0)  avail-
              able and has 3 chunks of 4 megabytes (order 10) available.

              If the memory is heavily fragmented, the counters for higher or-
              der chunks will be zero and allocation of large contiguous areas
              will fail.

              Further  information about the zones can be found in /proc/zone-
              info.

       /proc/bus
              Contains subdirectories for installed buses.

       /proc/bus/pccard
              Subdirectory for PCMCIA devices when  CONFIG_PCMCIA  is  set  at
              kernel compilation time.

       /proc/bus/pccard/drivers

       /proc/bus/pci
              Contains  various bus subdirectories and pseudo-files containing
              information about PCI buses, installed devices, and device driv-
              ers.  Some of these files are not ASCII.

       /proc/bus/pci/devices
              Information  about  PCI  devices.   They may be accessed through
              lspci(8) and setpci(8).

       /proc/cgroups (since Linux 2.6.24)
              See cgroups(7).

       /proc/cmdline
              Arguments passed to the Linux kernel at boot time.   Often  done
              via a boot manager such as lilo(8) or grub(8).

       /proc/config.gz (since Linux 2.6)
              This  file  exposes  the configuration options that were used to
              build the currently running kernel, in the same format  as  they
              would  be shown in the .config file that resulted when configur-
              ing the kernel (using make xconfig, make  config,  or  similar).
              The  file  contents  are  compressed;  view or search them using
              zcat(1) and zgrep(1).  As long as no changes have been  made  to
              the following file, the contents of /proc/config.gz are the same
              as those provided by:

                  cat /lib/modules/$(uname -r)/build/.config

              /proc/config.gz is provided only if  the  kernel  is  configured
              with CONFIG_IKCONFIG_PROC.

       /proc/crypto
              A  list  of  the ciphers provided by the kernel crypto API.  For
              details, see the kernel Linux Kernel  Crypto  API  documentation
              available   under   the   kernel   source  directory  Documenta-
              tion/crypto/ (or Documentation/DocBook before  Linux  4.10;  the
              documentation can be built using a command such as make htmldocs
              in the root directory of the kernel source tree).

       /proc/cpuinfo
              This is a collection of CPU and  system  architecture  dependent
              items,  for  each  supported architecture a different list.  Two
              common entries are processor which  gives  CPU  number  and  bo-
              gomips;  a system constant that is calculated during kernel ini-
              tialization.  SMP machines have information for each  CPU.   The
              lscpu(1) command gathers its information from this file.

       /proc/devices
              Text  listing  of  major numbers and device groups.  This can be
              used by MAKEDEV scripts for consistency with the kernel.

       /proc/diskstats (since Linux 2.5.69)
              This file contains disk I/O statistics  for  each  disk  device.
              See    the    Linux   kernel   source   file   Documentation/ad-
              min-guide/iostats.rst (or Documentation/iostats.txt before Linux
              5.3) for further information.

       /proc/dma
              This  is a list of the registered ISA DMA (direct memory access)
              channels in use.

       /proc/driver
              Empty subdirectory.

       /proc/execdomains
              List of the execution domains (ABI personalities).

       /proc/fb
              Frame buffer information when CONFIG_FB is defined during kernel
              compilation.

       /proc/filesystems
              A  text  listing  of  the filesystems which are supported by the
              kernel, namely filesystems which were compiled into  the  kernel
              or  whose  kernel  modules  are  currently  loaded.   (See  also
              filesystems(5).)  If a filesystem is marked with  "nodev",  this
              means  that  it  does  not  require a block device to be mounted
              (e.g., virtual filesystem, network filesystem).

              Incidentally, this file may be used by mount(8) when no filesys-
              tem  is specified and it didn't manage to determine the filesys-
              tem type.  Then filesystems contained in  this  file  are  tried
              (excepted those that are marked with "nodev").

       /proc/fs
              Contains subdirectories that in turn contain files with informa-
              tion about (certain) mounted filesystems.

       /proc/ide
              This directory exists on systems with the IDE  bus.   There  are
              directories for each IDE channel and attached device.  Files in-
              clude:

                  cache              buffer size in KB
                  capacity           number of sectors
                  driver             driver version
                  geometry           physical and logical geometry
                  identify           in hexadecimal
                  media              media type
                  model              manufacturer's model number
                  settings           drive settings
                  smart_thresholds   IDE disk management thresholds (in hex)
                  smart_values       IDE disk management values (in hex)

              The hdparm(8) utility provides access to this information  in  a
              friendly format.

       /proc/interrupts
              This  is  used to record the number of interrupts per CPU per IO
              device.  Since Linux 2.6.24, for the i386 and  x86-64  architec-
              tures,  at  least, this also includes interrupts internal to the
              system (that is, not associated with a device as such), such  as
              NMI  (nonmaskable  interrupt),  LOC (local timer interrupt), and
              for SMP systems, TLB (TLB flush  interrupt),  RES  (rescheduling
              interrupt),  CAL  (remote function call interrupt), and possibly
              others.  Very easy to read formatting, done in ASCII.

       /proc/iomem
              I/O memory map in Linux 2.4.

       /proc/ioports
              This is a list of currently registered Input-Output port regions
              that are in use.

       /proc/kallsyms (since Linux 2.5.71)
              This  holds  the  kernel exported symbol definitions used by the
              modules(X) tools to dynamically link and bind loadable  modules.
              In  Linux  2.5.47 and earlier, a similar file with slightly dif-
              ferent syntax was named ksyms.

       /proc/kcore
              This file represents the physical memory of the  system  and  is
              stored  in the ELF core file format.  With this pseudo-file, and
              an unstripped kernel (/usr/src/linux/vmlinux) binary, GDB can be
              used to examine the current state of any kernel data structures.

              The  total  length  of  the  file is the size of physical memory
              (RAM) plus 4 KiB.

       /proc/keys (since Linux 2.6.10)
              See keyrings(7).

       /proc/key-users (since Linux 2.6.10)
              See keyrings(7).

       /proc/kmsg
              This file can be used instead of the syslog(2)  system  call  to
              read  kernel messages.  A process must have superuser privileges
              to read this file, and only one process should read  this  file.
              This  file  should  not  be  read if a syslog process is running
              which uses the syslog(2) system call facility to log kernel mes-
              sages.

              Information in this file is retrieved with the dmesg(1) program.

       /proc/kpagecgroup (since Linux 4.3)
              This  file  contains  a 64-bit inode number of the memory cgroup
              each page is charged to, indexed by page frame number  (see  the
              discussion of /proc/pid/pagemap).

              The  /proc/kpagecgroup  file is present only if the CONFIG_MEMCG
              kernel configuration option is enabled.

       /proc/kpagecount (since Linux 2.6.25)
              This file contains a 64-bit count of the number  of  times  each
              physical page frame is mapped, indexed by page frame number (see
              the discussion of /proc/pid/pagemap).

              The  /proc/kpagecount  file  is  present  only   if   the   CON-
              FIG_PROC_PAGE_MONITOR kernel configuration option is enabled.

       /proc/kpageflags (since Linux 2.6.25)
              This  file  contains 64-bit masks corresponding to each physical
              page frame; it is indexed by page frame number (see the  discus-
              sion of /proc/pid/pagemap).  The bits are as follows:

                      0   -   KPF_LOCKED
                      1   -   KPF_ERROR
                      2   -   KPF_REFERENCED
                      3   -   KPF_UPTODATE
                      4   -   KPF_DIRTY
                      5   -   KPF_LRU
                      6   -   KPF_ACTIVE
                      7   -   KPF_SLAB
                      8   -   KPF_WRITEBACK
                      9   -   KPF_RECLAIM
                     10   -   KPF_BUDDY
                     11   -   KPF_MMAP            (since Linux 2.6.31)
                     12   -   KPF_ANON            (since Linux 2.6.31)
                     13   -   KPF_SWAPCACHE       (since Linux 2.6.31)
                     14   -   KPF_SWAPBACKED      (since Linux 2.6.31)
                     15   -   KPF_COMPOUND_HEAD   (since Linux 2.6.31)
                     16   -   KPF_COMPOUND_TAIL   (since Linux 2.6.31)
                     17   -   KPF_HUGE            (since Linux 2.6.31)
                     18   -   KPF_UNEVICTABLE     (since Linux 2.6.31)
                     19   -   KPF_HWPOISON        (since Linux 2.6.31)
                     20   -   KPF_NOPAGE          (since Linux 2.6.31)
                     21   -   KPF_KSM             (since Linux 2.6.32)
                     22   -   KPF_THP             (since Linux 3.4)

                     23   -   KPF_BALLOON         (since Linux 3.18)
                     24   -   KPF_ZERO_PAGE       (since Linux 4.0)
                     25   -   KPF_IDLE            (since Linux 4.3)

              For  further details on the meanings of these bits, see the ker-
              nel source file  Documentation/admin-guide/mm/pagemap.rst.   Be-
              fore  Linux  2.6.29,  KPF_WRITEBACK, KPF_RECLAIM, KPF_BUDDY, and
              KPF_LOCKED did not report correctly.

              The  /proc/kpageflags  file  is  present  only   if   the   CON-
              FIG_PROC_PAGE_MONITOR kernel configuration option is enabled.

       /proc/ksyms (Linux 1.1.23–2.5.47)
              See /proc/kallsyms.

       /proc/loadavg
              The  first  three  fields  in this file are load average figures
              giving the number of jobs in the run queue (state R) or  waiting
              for disk I/O (state D) averaged over 1, 5, and 15 minutes.  They
              are the same as the load average numbers given by uptime(1)  and
              other  programs.  The fourth field consists of two numbers sepa-
              rated by a slash (/).  The first of these is the number of  cur-
              rently runnable kernel scheduling entities (processes, threads).
              The value after the slash is the number of kernel scheduling en-
              tities  that  currently exist on the system.  The fifth field is
              the PID of the process that was most  recently  created  on  the
              system.

       /proc/locks
              This  file  shows current file locks (flock(2) and fcntl(2)) and
              leases (fcntl(2)).

              An example of the content shown in this file is the following:

                  1: POSIX  ADVISORY  READ  5433 08:01:7864448 128 128
                  2: FLOCK  ADVISORY  WRITE 2001 08:01:7864554 0 EOF
                  3: FLOCK  ADVISORY  WRITE 1568 00:2f:32388 0 EOF
                  4: POSIX  ADVISORY  WRITE 699 00:16:28457 0 EOF
                  5: POSIX  ADVISORY  WRITE 764 00:16:21448 0 0
                  6: POSIX  ADVISORY  READ  3548 08:01:7867240 1 1
                  7: POSIX  ADVISORY  READ  3548 08:01:7865567 1826 2335
                  8: OFDLCK ADVISORY  WRITE -1 08:01:8713209 128 191

              The fields shown in each line are as follows:

              [1]  The ordinal position of the lock in the list.

              [2]  The lock type.  Values that may appear here include:

                   FLOCK  This is a BSD file lock created using flock(2).

                   OFDLCK This is an open file description (OFD) lock  created
                          using fcntl(2).

                   POSIX  This  is  a  POSIX byte-range lock created using fc-
                          ntl(2).

              [3]  Among the strings that can appear here are the following:

                   ADVISORY
                          This is an advisory lock.

                   MANDATORY
                          This is a mandatory lock.

              [4]  The type of lock.  Values that can appear here are:

                   READ   This is a POSIX or OFD read lock, or  a  BSD  shared
                          lock.

                   WRITE  This  is  a POSIX or OFD write lock, or a BSD exclu-
                          sive lock.

              [5]  The PID of the process that owns the lock.

                   Because OFD locks are not owned by a single process  (since
                   multiple  processes may have file descriptors that refer to
                   the same open file description), the value -1 is  displayed
                   in  this  field  for  OFD locks.  (Before Linux 4.14, a bug
                   meant that the PID of the process that  initially  acquired
                   the lock was displayed instead of the value -1.)

              [6]  Three colon-separated subfields that identify the major and
                   minor device ID of the  device  containing  the  filesystem
                   where the locked file resides, followed by the inode number
                   of the locked file.

              [7]  The byte offset of the first byte of  the  lock.   For  BSD
                   locks, this value is always 0.

              [8]  The  byte offset of the last byte of the lock.  EOF in this
                   field means that the lock extends to the end of  the  file.
                   For BSD locks, the value shown is always EOF.

              Since  Linux 4.9, the list of locks shown in /proc/locks is fil-
              tered to show just the locks for the processes in the PID  name-
              space (see pid_namespaces(7)) for which the /proc filesystem was
              mounted.  (In the initial PID namespace, there is  no  filtering
              of the records shown in this file.)

              The  lslocks(8)  command  provides  a bit more information about
              each lock.

       /proc/malloc (only up to and including Linux 2.2)
              This file is present only  if  CONFIG_DEBUG_MALLOC  was  defined
              during compilation.

       /proc/meminfo
              This  file  reports statistics about memory usage on the system.
              It is used by free(1) to report the amount of free and used mem-
              ory (both physical and swap) on the system as well as the shared
              memory and buffers used by the kernel.  Each line  of  the  file
              consists  of a parameter name, followed by a colon, the value of
              the parameter, and an option unit of measurement  (e.g.,  "kB").
              The  list  below  describes  the  parameter names and the format
              specifier required to read the field value.  Except as noted be-
              low,  all  of  the fields have been present since at least Linux
              2.6.0.  Some fields are displayed only if the kernel was config-
              ured  with  various options; those dependencies are noted in the
              list.

              MemTotal %lu
                     Total usable RAM (i.e., physical RAM minus a few reserved
                     bits and the kernel binary code).

              MemFree %lu
                     The sum of LowFree+HighFree.

              MemAvailable %lu (since Linux 3.14)
                     An  estimate of how much memory is available for starting
                     new applications, without swapping.

              Buffers %lu
                     Relatively temporary storage for  raw  disk  blocks  that
                     shouldn't get tremendously large (20 MB or so).

              Cached %lu
                     In-memory  cache  for  files read from the disk (the page
                     cache).  Doesn't include SwapCached.

              SwapCached %lu
                     Memory that once was swapped out, is swapped back in  but
                     still  also  is in the swap file.  (If memory pressure is
                     high, these pages don't need to be swapped out again  be-
                     cause  they  are  already  in  the swap file.  This saves
                     I/O.)

              Active %lu
                     Memory that has been used more recently and  usually  not
                     reclaimed unless absolutely necessary.

              Inactive %lu
                     Memory which has been less recently used.  It is more el-
                     igible to be reclaimed for other purposes.

              Active(anon) %lu (since Linux 2.6.28)
                     [To be documented.]

              Inactive(anon) %lu (since Linux 2.6.28)
                     [To be documented.]

              Active(file) %lu (since Linux 2.6.28)
                     [To be documented.]

              Inactive(file) %lu (since Linux 2.6.28)
                     [To be documented.]

              Unevictable %lu (since Linux 2.6.28)
                     (From  Linux   2.6.28   to   Linux   2.6.30,   CONFIG_UN-
                     EVICTABLE_LRU was required.)  [To be documented.]

              Mlocked %lu (since Linux 2.6.28)
                     (From   Linux   2.6.28   to   Linux   2.6.30,  CONFIG_UN-
                     EVICTABLE_LRU was required.)  [To be documented.]

              HighTotal %lu
                     (Starting with Linux 2.6.19, CONFIG_HIGHMEM is required.)
                     Total  amount  of  highmem.   Highmem is all memory above
                     ~860 MB of physical memory.  Highmem areas are for use by
                     user-space  programs,  or for the page cache.  The kernel
                     must use tricks to access this memory, making  it  slower
                     to access than lowmem.

              HighFree %lu
                     (Starting with Linux 2.6.19, CONFIG_HIGHMEM is required.)
                     Amount of free highmem.

              LowTotal %lu
                     (Starting with Linux 2.6.19, CONFIG_HIGHMEM is required.)
                     Total  amount  of  lowmem.  Lowmem is memory which can be
                     used for everything that highmem can be used for, but  it
                     is  also  available for the kernel's use for its own data
                     structures.  Among many other things, it is where  every-
                     thing  from  Slab  is  allocated.  Bad things happen when
                     you're out of lowmem.

              LowFree %lu
                     (Starting with Linux 2.6.19, CONFIG_HIGHMEM is required.)
                     Amount of free lowmem.

              MmapCopy %lu (since Linux 2.6.29)
                     (CONFIG_MMU is required.)  [To be documented.]

              SwapTotal %lu
                     Total amount of swap space available.

              SwapFree %lu
                     Amount of swap space that is currently unused.

              Dirty %lu
                     Memory which is waiting to get written back to the disk.

              Writeback %lu
                     Memory which is actively being written back to the disk.

              AnonPages %lu (since Linux 2.6.18)
                     Non-file backed pages mapped into user-space page tables.

              Mapped %lu
                     Files  which have been mapped into memory (with mmap(2)),
                     such as libraries.

              Shmem %lu (since Linux 2.6.32)
                     Amount of memory consumed in tmpfs(5) filesystems.

              KReclaimable %lu (since Linux 4.20)
                     Kernel allocations that the kernel will  attempt  to  re-
                     claim  under memory pressure.  Includes SReclaimable (be-
                     low), and other direct allocations with a shrinker.

              Slab %lu
                     In-kernel data structures cache.  (See slabinfo(5).)

              SReclaimable %lu (since Linux 2.6.19)
                     Part of Slab, that might be reclaimed, such as caches.

              SUnreclaim %lu (since Linux 2.6.19)
                     Part of Slab, that cannot be reclaimed  on  memory  pres-
                     sure.

              KernelStack %lu (since Linux 2.6.32)
                     Amount of memory allocated to kernel stacks.

              PageTables %lu (since Linux 2.6.18)
                     Amount  of  memory  dedicated to the lowest level of page
                     tables.

              Quicklists %lu (since Linux 2.6.27)
                     (CONFIG_QUICKLIST is required.)  [To be documented.]

              NFS_Unstable %lu (since Linux 2.6.18)
                     NFS pages sent to the server, but not  yet  committed  to
                     stable storage.

              Bounce %lu (since Linux 2.6.18)
                     Memory used for block device "bounce buffers".

              WritebackTmp %lu (since Linux 2.6.26)
                     Memory used by FUSE for temporary writeback buffers.

              CommitLimit %lu (since Linux 2.6.10)
                     This is the total amount of memory currently available to
                     be allocated on the system, expressed in kilobytes.  This
                     limit  is adhered to only if strict overcommit accounting
                     is enabled (mode  2  in  /proc/sys/vm/overcommit_memory).
                     The  limit  is  calculated  according  to the formula de-
                     scribed under /proc/sys/vm/overcommit_memory.   For  fur-
                     ther  details,  see  the  kernel  source  file Documenta-
                     tion/vm/overcommit-accounting.rst.

              Committed_AS %lu
                     The amount of memory presently allocated on  the  system.
                     The  committed memory is a sum of all of the memory which
                     has been allocated by processes, even if it has not  been
                     "used" by them as of yet.  A process which allocates 1 GB
                     of memory (using malloc(3) or similar), but touches  only
                     300  MB  of that memory will show up as using only 300 MB
                     of memory even if it has the address space allocated  for
                     the entire 1 GB.

                     This  1 GB is memory which has been "committed" to by the
                     VM and can be used at any time by the allocating applica-
                     tion.  With strict overcommit enabled on the system (mode
                     2 in /proc/sys/vm/overcommit_memory),  allocations  which
                     would exceed the CommitLimit will not be permitted.  This
                     is useful if one needs to guarantee that  processes  will
                     not  fail due to lack of memory once that memory has been
                     successfully allocated.

              VmallocTotal %lu
                     Total size of vmalloc memory area.

              VmallocUsed %lu
                     Amount of vmalloc area which is used.  Since  Linux  4.4,
                     this  field is no longer calculated, and is hard coded as
                     0.  See /proc/vmallocinfo.

              VmallocChunk %lu
                     Largest contiguous block of vmalloc area which  is  free.
                     Since  Linux  4.4, this field is no longer calculated and
                     is hard coded as 0.  See /proc/vmallocinfo.

              HardwareCorrupted %lu (since Linux 2.6.32)
                     (CONFIG_MEMORY_FAILURE is required.)  [To be documented.]

              LazyFree %lu (since Linux 4.12)
                     Shows  the  amount  of  memory   marked   by   madvise(2)
                     MADV_FREE.

              AnonHugePages %lu (since Linux 2.6.38)
                     (CONFIG_TRANSPARENT_HUGEPAGE   is   required.)   Non-file
                     backed huge pages mapped into user-space page tables.

              ShmemHugePages %lu (since Linux 4.8)
                     (CONFIG_TRANSPARENT_HUGEPAGE is required.)   Memory  used
                     by shared memory (shmem) and tmpfs(5) allocated with huge
                     pages.

              ShmemPmdMapped %lu (since Linux 4.8)
                     (CONFIG_TRANSPARENT_HUGEPAGE is required.)  Shared memory
                     mapped into user space with huge pages.

              CmaTotal %lu (since Linux 3.1)
                     Total  CMA  (Contiguous  Memory  Allocator) pages.  (CON-
                     FIG_CMA is required.)

              CmaFree %lu (since Linux 3.1)
                     Free CMA  (Contiguous  Memory  Allocator)  pages.   (CON-
                     FIG_CMA is required.)

              HugePages_Total %lu
                     (CONFIG_HUGETLB_PAGE  is required.)  The size of the pool
                     of huge pages.

              HugePages_Free %lu
                     (CONFIG_HUGETLB_PAGE is required.)  The  number  of  huge
                     pages in the pool that are not yet allocated.

              HugePages_Rsvd %lu (since Linux 2.6.17)
                     (CONFIG_HUGETLB_PAGE is required.)  This is the number of
                     huge pages for which a commitment to  allocate  from  the
                     pool  has been made, but no allocation has yet been made.
                     These reserved huge pages guarantee that  an  application
                     will  be  able  to  allocate a huge page from the pool of
                     huge pages at fault time.

              HugePages_Surp %lu (since Linux 2.6.24)
                     (CONFIG_HUGETLB_PAGE is required.)  This is the number of
                     huge   pages   in   the   pool   above   the   value   in
                     /proc/sys/vm/nr_hugepages.  The maximum number of surplus
                     huge  pages  is  controlled  by  /proc/sys/vm/nr_overcom-
                     mit_hugepages.

              Hugepagesize %lu
                     (CONFIG_HUGETLB_PAGE is  required.)   The  size  of  huge
                     pages.

              DirectMap4k %lu (since Linux 2.6.27)
                     Number  of bytes of RAM linearly mapped by kernel in 4 kB
                     pages.  (x86.)

              DirectMap4M %lu (since Linux 2.6.27)
                     Number of bytes of RAM linearly mapped by kernel in 4  MB
                     pages.   (x86  with  CONFIG_X86_64  or CONFIG_X86_PAE en-
                     abled.)

              DirectMap2M %lu (since Linux 2.6.27)
                     Number of bytes of RAM linearly mapped by kernel in 2  MB
                     pages.    (x86   with   neither  CONFIG_X86_64  nor  CON-
                     FIG_X86_PAE enabled.)

              DirectMap1G %lu (since Linux 2.6.27)
                     (x86 with CONFIG_X86_64 and CONFIG_X86_DIRECT_GBPAGES en-
                     abled.)

       /proc/modules
              A  text list of the modules that have been loaded by the system.
              See also lsmod(8).

       /proc/mounts
              Before Linux 2.4.19, this file was a list of all the filesystems
              currently  mounted on the system.  With the introduction of per-
              process  mount  namespaces  in  Linux  2.4.19  (see  mount_name-
              spaces(7)),  this file became a link to /proc/self/mounts, which
              lists the mounts of the process's own mount namespace.  The for-
              mat of this file is documented in fstab(5).

       /proc/mtrr
              Memory  Type  Range Registers.  See the Linux kernel source file
              Documentation/x86/mtrr.rst (or Documentation/x86/mtrr.txt before
              Linux  5.2,  or  Documentation/mtrr.txt before Linux 2.6.28) for
              details.

       /proc/net
              This directory contains various files  and  subdirectories  con-
              taining  information about the networking layer.  The files con-
              tain ASCII structures and are, therefore, readable with  cat(1).
              However, the standard netstat(8) suite provides much cleaner ac-
              cess to these files.

              With the advent of network namespaces, various  information  re-
              lating  to  the  network stack is virtualized (see network_name-
              spaces(7)).  Thus, since Linux 2.6.25, /proc/net is  a  symbolic
              link  to  the  directory /proc/self/net, which contains the same
              files and directories as listed below.  However, these files and
              directories  now expose information for the network namespace of
              which the process is a member.

       /proc/net/arp
              This holds an ASCII readable dump of the kernel ARP  table  used
              for  address resolutions.  It will show both dynamically learned
              and preprogrammed ARP entries.  The format is:

                  IP address     HW type   Flags     HW address          Mask   Device
                  192.168.0.50   0x1       0x2       00:50:BF:25:68:F3   *      eth0
                  192.168.0.250  0x1       0xc       00:00:00:00:00:00   *      eth0

              Here "IP address" is the IPv4 address of the machine and the "HW
              type"  is  the  hardware  type of the address from RFC 826.  The
              flags are the internal flags of the ARP structure (as defined in
              /usr/include/linux/if_arp.h)  and  the  "HW address" is the data
              link layer mapping for that IP address if it is known.

       /proc/net/dev
              The dev pseudo-file contains network device status  information.
              This  gives  the number of received and sent packets, the number
              of errors and collisions and other basic statistics.  These  are
              used  by  the  ifconfig(8) program to report device status.  The
              format is:

              Inter-|   Receive                                                |  Transmit
               face |bytes    packets errs drop fifo frame compressed multicast|bytes    packets errs drop fifo colls carrier compressed
                  lo: 2776770   11307    0    0    0     0          0         0  2776770   11307    0    0    0     0       0          0
                eth0: 1215645    2751    0    0    0     0          0         0  1782404    4324    0    0    0   427       0          0
                ppp0: 1622270    5552    1    0    0     0          0         0   354130    5669    0    0    0     0       0          0
                tap0:    7714      81    0    0    0     0          0         0     7714      81    0    0    0     0       0          0

       /proc/net/dev_mcast
              Defined in /usr/src/linux/net/core/dev_mcast.c:

                  indx interface_name  dmi_u dmi_g dmi_address
                  2    eth0            1     0     01005e000001
                  3    eth1            1     0     01005e000001
                  4    eth2            1     0     01005e000001

       /proc/net/igmp
              Internet    Group    Management    Protocol.      Defined     in
              /usr/src/linux/net/core/igmp.c.

       /proc/net/rarp
              This  file uses the same format as the arp file and contains the
              current reverse mapping database used to provide rarp(8) reverse
              address  lookup  services.   If  RARP is not configured into the
              kernel, this file will not be present.

       /proc/net/raw
              Holds a dump of the RAW socket table.  Much of  the  information
              is  not of use apart from debugging.  The "sl" value is the ker-
              nel hash slot for the socket, the "local_address" is  the  local
              address  and  protocol number pair.  "St" is the internal status
              of the socket.  The "tx_queue" and "rx_queue" are  the  outgoing
              and  incoming  data  queue in terms of kernel memory usage.  The
              "tr", "tm->when", and "rexmits" fields are not used by RAW.  The
              "uid"  field  holds  the  effective  UID  of  the creator of the
              socket.

       /proc/net/snmp
              This file holds the ASCII data needed for the IP, ICMP, TCP, and
              UDP management information bases for an SNMP agent.

       /proc/net/tcp
              Holds  a  dump of the TCP socket table.  Much of the information
              is not of use apart from debugging.  The "sl" value is the  ker-
              nel  hash  slot for the socket, the "local_address" is the local
              address and port number pair.  The "rem_address" is  the  remote
              address and port number pair (if connected).  "St" is the inter-
              nal status of the socket.  The "tx_queue" and "rx_queue" are the
              outgoing  and  incoming data queue in terms of kernel memory us-
              age.  The "tr", "tm->when", and "rexmits" fields  hold  internal
              information  of  the kernel socket state and are useful only for
              debugging.  The "uid" field holds the effective UID of the  cre-
              ator of the socket.

       /proc/net/udp
              Holds  a  dump of the UDP socket table.  Much of the information
              is not of use apart from debugging.  The "sl" value is the  ker-
              nel  hash  slot for the socket, the "local_address" is the local
              address and port number pair.  The "rem_address" is  the  remote
              address and port number pair (if connected).  "St" is the inter-
              nal status of the socket.  The "tx_queue" and "rx_queue" are the
              outgoing  and  incoming data queue in terms of kernel memory us-
              age.  The "tr", "tm->when", and "rexmits" fields are not used by
              UDP.   The "uid" field holds the effective UID of the creator of
              the socket.  The format is:

              sl  local_address rem_address   st tx_queue rx_queue tr rexmits  tm->when uid
               1: 01642C89:0201 0C642C89:03FF 01 00000000:00000001 01:000071BA 00000000 0
               1: 00000000:0801 00000000:0000 0A 00000000:00000000 00:00000000 6F000100 0
               1: 00000000:0201 00000000:0000 0A 00000000:00000000 00:00000000 00000000 0

       /proc/net/unix
              Lists the UNIX domain sockets  present  within  the  system  and
              their status.  The format is:

              Num RefCount Protocol Flags    Type St Inode Path
               0: 00000002 00000000 00000000 0001 03    42
               1: 00000001 00000000 00010000 0001 01  1948 /dev/printer

              The fields are as follows:

              Num:      the kernel table slot number.

              RefCount: the number of users of the socket.

              Protocol: currently always 0.

              Flags:    the  internal  kernel  flags holding the status of the
                        socket.

              Type:     the socket type.  For  SOCK_STREAM  sockets,  this  is
                        0001;  for  SOCK_DGRAM  sockets,  it  is 0002; and for
                        SOCK_SEQPACKET sockets, it is 0005.

              St:       the internal state of the socket.

              Inode:    the inode number of the socket.

              Path:     the bound pathname (if any) of the socket.  Sockets in
                        the  abstract  namespace are included in the list, and
                        are shown with a Path that commences with the  charac-
                        ter '@'.

       /proc/net/netfilter/nfnetlink_queue
              This file contains information about netfilter user-space queue-
              ing, if used.  Each line represents a queue.  Queues  that  have
              not been subscribed to by user space are not shown.

                     1   4207     0  2 65535     0     0        0  1
                    (1)   (2)    (3)(4)  (5)    (6)   (7)      (8)

              The fields in each line are:

              (1)  The ID of the queue.  This matches what is specified in the
                   --queue-num or --queue-balance options to  the  iptables(8)
                   NFQUEUE target.  See iptables-extensions(8) for more infor-
                   mation.

              (2)  The netlink port ID subscribed to the queue.

              (3)  The number of packets currently queued and  waiting  to  be
                   processed by the application.

              (4)  The copy mode of the queue.  It is either 1 (metadata only)
                   or 2 (also copy payload data to user space).

              (5)  Copy range; that is,  how  many  bytes  of  packet  payload
                   should be copied to user space at most.

              (6)  queue dropped.  Number of packets that had to be dropped by
                   the kernel because too many packets are already waiting for
                   user space to send back the mandatory accept/drop verdicts.

              (7)  queue  user  dropped.   Number of packets that were dropped
                   within the netlink subsystem.  Such  drops  usually  happen
                   when the corresponding socket buffer is full; that is, user
                   space is not able to read messages fast enough.

              (8)  sequence number.  Every queued packet is associated with  a
                   (32-bit)  monotonically  increasing  sequence number.  This
                   shows the ID of the most recent packet queued.

              The last number exists only for compatibility reasons and is al-
              ways 1.

       /proc/partitions
              Contains  the  major and minor numbers of each partition as well
              as the number of 1024-byte blocks and the partition name.

       /proc/pci
              This is a listing of all PCI devices found  during  kernel  ini-
              tialization and their configuration.

              This  file has been deprecated in favor of a new /proc interface
              for PCI  (/proc/bus/pci).   It  became  optional  in  Linux  2.2
              (available  with CONFIG_PCI_OLD_PROC set at kernel compilation).
              It became once more nonoptionally enabled in Linux  2.4.   Next,
              it  was  deprecated  in  Linux  2.6  (still  available with CON-
              FIG_PCI_LEGACY_PROC set), and finally removed  altogether  since
              Linux 2.6.17.

       /proc/profile (since Linux 2.4)
              This file is present only if the kernel was booted with the pro-
              file=1 command-line option.  It exposes kernel profiling  infor-
              mation  in  a  binary format for use by readprofile(1).  Writing
              (e.g., an empty string) to this file resets the profiling  coun-
              ters; on some architectures, writing a binary integer "profiling
              multiplier" of size sizeof(int)  sets  the  profiling  interrupt
              frequency.

       /proc/scsi
              A directory with the scsi mid-level pseudo-file and various SCSI
              low-level driver directories, which contain a file for each SCSI
              host  in  this system, all of which give the status of some part
              of the SCSI IO subsystem.  These files contain ASCII  structures
              and are, therefore, readable with cat(1).

              You  can also write to some of the files to reconfigure the sub-
              system or switch certain features on or off.

       /proc/scsi/scsi
              This is a listing of all SCSI devices known to the kernel.   The
              listing  is  similar  to  the one seen during bootup.  scsi cur-
              rently supports only the add-single-device command which  allows
              root to add a hotplugged device to the list of known devices.

              The command

                  echo 'scsi add-single-device 1 0 5 0' > /proc/scsi/scsi

              will  cause host scsi1 to scan on SCSI channel 0 for a device on
              ID 5 LUN 0.  If there is already a device known on this  address
              or the address is invalid, an error will be returned.

       /proc/scsi/drivername
              drivername   can   currently  be  NCR53c7xx,  aha152x,  aha1542,
              aha1740, aic7xxx, buslogic, eata_dma, eata_pio, fdomain, in2000,
              pas16,  qlogic,  scsi_debug, seagate, t128, u15-24f, ultrastore,
              or wd7000.  These directories show up for all drivers that  reg-
              istered  at  least  one  SCSI HBA.  Every directory contains one
              file per registered host.  Every host-file is  named  after  the
              number the host was assigned during initialization.

              Reading these files will usually show driver and host configura-
              tion, statistics, and so on.

              Writing to these files  allows  different  things  on  different
              hosts.   For  example,  with the latency and nolatency commands,
              root can switch on and off command latency measurement  code  in
              the  eata_dma driver.  With the lockup and unlock commands, root
              can control bus lockups simulated by the scsi_debug driver.

       /proc/self
              This  directory  refers  to  the  process  accessing  the  /proc
              filesystem, and is identical to the /proc directory named by the
              process ID of the same process.

       /proc/slabinfo
              Information about kernel caches.  See slabinfo(5) for details.

       /proc/stat
              kernel/system statistics.  Varies with architecture.  Common en-
              tries include:

              cpu 10132153 290696 3084719 46828483 16683 0 25195 0 175628 0
              cpu0 1393280 32966 572056 13343292 6130 0 17875 0 23933 0
                     The   amount  of  time,  measured  in  units  of  USER_HZ
                     (1/100ths  of  a  second  on  most   architectures,   use
                     sysconf(_SC_CLK_TCK) to obtain the right value), that the
                     system ("cpu" line) or the  specific  CPU  ("cpuN"  line)
                     spent in various states:

                     user   (1) Time spent in user mode.

                     nice   (2)  Time  spent  in  user  mode with low priority
                            (nice).

                     system (3) Time spent in system mode.

                     idle   (4) Time spent  in  the  idle  task.   This  value
                            should  be  USER_HZ  times the second entry in the
                            /proc/uptime pseudo-file.

                     iowait (since Linux 2.5.41)
                            (5) Time waiting for I/O to complete.  This  value
                            is not reliable, for the following reasons:

                            •  The  CPU  will  not  wait  for I/O to complete;
                               iowait is the time that a task is  waiting  for
                               I/O  to  complete.   When  a CPU goes into idle
                               state for outstanding task  I/O,  another  task
                               will be scheduled on this CPU.

                            •  On  a  multi-core CPU, the task waiting for I/O
                               to complete is not running on any CPU,  so  the
                               iowait of each CPU is difficult to calculate.

                            •  The value in this field may decrease in certain
                               conditions.

                     irq (since Linux 2.6.0)
                            (6) Time servicing interrupts.

                     softirq (since Linux 2.6.0)
                            (7) Time servicing softirqs.

                     steal (since Linux 2.6.11)
                            (8) Stolen time, which is the time spent in  other
                            operating  systems  when  running in a virtualized
                            environment

                     guest (since Linux 2.6.24)
                            (9) Time spent running a virtual CPU for guest op-
                            erating  systems  under  the  control of the Linux
                            kernel.

                     guest_nice (since Linux 2.6.33)
                            (10) Time spent running a niced guest (virtual CPU
                            for  guest  operating systems under the control of
                            the Linux kernel).

              page 5741 1808
                     The number of pages the system paged in  and  the  number
                     that were paged out (from disk).

              swap 1 0
                     The  number  of  swap pages that have been brought in and
                     out.

              intr 1462898
                     This line shows counts of interrupts serviced since  boot
                     time,  for  each  of the possible system interrupts.  The
                     first column is the total of all interrupts serviced  in-
                     cluding unnumbered architecture specific interrupts; each
                     subsequent column is the total for that  particular  num-
                     bered  interrupt.   Unnumbered  interrupts are not shown,
                     only summed into the total.

              disk_io: (2,0):(31,30,5764,1,2) (3,0):...
                     (major,disk_idx):(noinfo,     read_io_ops,     blks_read,
                     write_io_ops, blks_written)
                     (Linux 2.4 only)

              ctxt 115315
                     The number of context switches that the system underwent.

              btime 769041601
                     boot   time,  in  seconds  since  the  Epoch,  1970-01-01
                     00:00:00 +0000 (UTC).

              processes 86031
                     Number of forks since boot.

              procs_running 6
                     Number of processes in runnable state.  (Linux 2.5.45 on-
                     ward.)

              procs_blocked 2
                     Number  of processes blocked waiting for I/O to complete.
                     (Linux 2.5.45 onward.)

              softirq 229245889 94 60001584 13619 5175704 2471304 28  51212741
              59130143 0 51240672
                     This  line shows the number of softirq for all CPUs.  The
                     first column is the total of all softirqs and each subse-
                     quent column is the total for particular softirq.  (Linux
                     2.6.31 onward.)

       /proc/swaps
              Swap areas in use.  See also swapon(8).

       /proc/sys
              This directory (present since Linux 1.3.57) contains a number of
              files  and  subdirectories  corresponding  to  kernel variables.
              These variables can be read and in some cases modified using the
              /proc filesystem, and the (deprecated) sysctl(2) system call.

              String values may be terminated by either '\0' or '\n'.

              Integer  and  long values may be written either in decimal or in
              hexadecimal notation (e.g., 0x3FFF).  When writing multiple  in-
              teger  or long values, these may be separated by any of the fol-
              lowing whitespace characters: ' ', '\t', or '\n'.   Using  other
              separators leads to the error EINVAL.

       /proc/sys/abi (since Linux 2.4.10)
              This  directory may contain files with application binary infor-
              mation.   See  the   Linux   kernel   source   file   Documenta-
              tion/sysctl/abi.rst   (or   Documentation/sysctl/abi.txt  before
              Linux 5.3) for more information.

       /proc/sys/debug
              This directory may be empty.

       /proc/sys/dev
              This  directory  contains  device-specific  information   (e.g.,
              dev/cdrom/info).  On some systems, it may be empty.

       /proc/sys/fs
              This  directory contains the files and subdirectories for kernel
              variables related to filesystems.

       /proc/sys/fs/aio-max-nr and /proc/sys/fs/aio-nr (since Linux 2.6.4)
              aio-nr is the running total of the number of events specified by
              io_setup(2)  calls  for  all  currently active AIO contexts.  If
              aio-nr reaches aio-max-nr, then io_setup(2) will fail  with  the
              error  EAGAIN.  Raising aio-max-nr does not result in the preal-
              location or resizing of any kernel data structures.

       /proc/sys/fs/binfmt_misc
              Documentation for files in this directory can be  found  in  the
              Linux    kernel    source    in   the   file   Documentation/ad-
              min-guide/binfmt-misc.rst (or  in  Documentation/binfmt_misc.txt
              on older kernels).

       /proc/sys/fs/dentry-state (since Linux 2.2)
              This file contains information about the status of the directory
              cache (dcache).   The  file  contains  six  numbers,  nr_dentry,
              nr_unused,  age_limit  (age  in  seconds), want_pages (pages re-
              quested by system) and two dummy values.

              •  nr_dentry is the number of  allocated  dentries  (dcache  en-
                 tries).  This field is unused in Linux 2.2.

              •  nr_unused is the number of unused dentries.

              •  age_limit  is  the  age in seconds after which dcache entries
                 can be reclaimed when memory is short.

              •  want_pages  is   nonzero   when   the   kernel   has   called
                 shrink_dcache_pages() and the dcache isn't pruned yet.

       /proc/sys/fs/dir-notify-enable
              This file can be used to disable or enable the dnotify interface
              described in fcntl(2) on a system-wide basis.  A value of  0  in
              this file disables the interface, and a value of 1 enables it.

       /proc/sys/fs/dquot-max
              This file shows the maximum number of cached disk quota entries.
              On some (2.4) systems, it is not present.  If the number of free
              cached  disk quota entries is very low and you have some awesome
              number of simultaneous system users, you might want to raise the
              limit.

       /proc/sys/fs/dquot-nr
              This  file  shows the number of allocated disk quota entries and
              the number of free disk quota entries.

       /proc/sys/fs/epoll (since Linux 2.6.28)
              This directory contains the file max_user_watches, which can  be
              used  to limit the amount of kernel memory consumed by the epoll
              interface.  For further details, see epoll(7).

       /proc/sys/fs/file-max
              This file defines a system-wide limit  on  the  number  of  open
              files for all processes.  System calls that fail when encounter-
              ing this limit fail with the  error  ENFILE.   (See  also  setr-
              limit(2),  which can be used by a process to set the per-process
              limit, RLIMIT_NOFILE, on the number of files it may  open.)   If
              you  get  lots of error messages in the kernel log about running
              out of file handles (open file  descriptions)  (look  for  "VFS:
              file-max limit <number> reached"), try increasing this value:

                  echo 100000 > /proc/sys/fs/file-max

              Privileged  processes  (CAP_SYS_ADMIN) can override the file-max
              limit.

       /proc/sys/fs/file-nr
              This (read-only) file contains three numbers: the number of  al-
              located  file  handles  (i.e.,  the number of open file descrip-
              tions; see open(2)); the number of free file  handles;  and  the
              maximum  number  of  file  handles  (i.e.,  the  same  value  as
              /proc/sys/fs/file-max).  If the number of allocated file handles
              is close to the maximum, you should consider increasing the max-
              imum.  Before Linux 2.6, the kernel allocated file  handles  dy-
              namically, but it didn't free them again.  Instead the free file
              handles were kept in a list for  reallocation;  the  "free  file
              handles"  value indicates the size of that list.  A large number
              of free file handles indicates that there was a past peak in the
              usage  of  open  file handles.  Since Linux 2.6, the kernel does
              deallocate freed file handles, and the "free file handles" value
              is always zero.

       /proc/sys/fs/inode-max (only present until Linux 2.2)
              This file contains the maximum number of in-memory inodes.  This
              value should be 3–4 times larger than  the  value  in  file-max,
              since  stdin,  stdout  and network sockets also need an inode to
              handle them.  When you regularly run out of inodes, you need  to
              increase this value.

              Starting  with  Linux  2.4, there is no longer a static limit on
              the number of inodes, and this file is removed.

       /proc/sys/fs/inode-nr
              This file contains the first two values from inode-state.

       /proc/sys/fs/inode-state
              This file contains  seven  numbers:  nr_inodes,  nr_free_inodes,
              preshrink, and four dummy values (always zero).

              nr_inodes  is  the  number  of  inodes the system has allocated.
              nr_free_inodes represents the number of free inodes.

              preshrink is nonzero when the nr_inodes > inode-max and the sys-
              tem  needs  to  prune the inode list instead of allocating more;
              since Linux 2.4, this field is a dummy value (always zero).

       /proc/sys/fs/inotify (since Linux 2.6.13)
              This directory contains  files  max_queued_events,  max_user_in-
              stances,  and  max_user_watches,  that  can be used to limit the
              amount of kernel memory consumed by the inotify interface.   For
              further details, see inotify(7).

       /proc/sys/fs/lease-break-time
              This file specifies the grace period that the kernel grants to a
              process holding a file lease (fcntl(2)) after it has sent a sig-
              nal to that process notifying it that another process is waiting
              to open the file.  If the lease holder does not remove or  down-
              grade  the  lease  within this grace period, the kernel forcibly
              breaks the lease.

       /proc/sys/fs/leases-enable
              This file can be used to enable  or  disable  file  leases  (fc-
              ntl(2)) on a system-wide basis.  If this file contains the value
              0, leases are disabled.  A nonzero value enables leases.

       /proc/sys/fs/mount-max (since Linux 4.9)
              The value in this file specifies the maximum  number  of  mounts
              that  may exist in a mount namespace.  The default value in this
              file is 100,000.

       /proc/sys/fs/mqueue (since Linux 2.6.6)
              This  directory  contains  files   msg_max,   msgsize_max,   and
              queues_max,  controlling  the  resources  used  by POSIX message
              queues.  See mq_overview(7) for details.

       /proc/sys/fs/nr_open (since Linux 2.6.25)
              This  file  imposes  a  ceiling  on  the  value  to  which   the
              RLIMIT_NOFILE  resource  limit can be raised (see getrlimit(2)).
              This ceiling is enforced for both  unprivileged  and  privileged
              process.   The  default  value in this file is 1048576.  (Before
              Linux 2.6.25, the ceiling for RLIMIT_NOFILE  was  hard-coded  to
              the same value.)

       /proc/sys/fs/overflowgid and /proc/sys/fs/overflowuid
              These  files  allow you to change the value of the fixed UID and
              GID.  The default  is  65534.   Some  filesystems  support  only
              16-bit  UIDs  and  GIDs,  although in Linux UIDs and GIDs are 32
              bits.  When one of these filesystems is mounted with writes  en-
              abled,  any  UID or GID that would exceed 65535 is translated to
              the overflow value before being written to disk.

       /proc/sys/fs/pipe-max-size (since Linux 2.6.35)
              See pipe(7).

       /proc/sys/fs/pipe-user-pages-hard (since Linux 4.5)
              See pipe(7).

       /proc/sys/fs/pipe-user-pages-soft (since Linux 4.5)
              See pipe(7).

       /proc/sys/fs/protected_fifos (since Linux 4.19)
              The value in this file is/can be set to one of the following:

              0   Writing to FIFOs is unrestricted.

              1   Don't allow O_CREAT open(2) on FIFOs that the caller doesn't
                  own in world-writable sticky directories, unless the FIFO is
                  owned by the owner of the directory.

              2   As for the value 1, but  the  restriction  also  applies  to
                  group-writable sticky directories.

              The  intent  of  the above protections is to avoid unintentional
              writes to an attacker-controlled FIFO when a program expected to
              create a regular file.

       /proc/sys/fs/protected_hardlinks (since Linux 3.6)
              When  the value in this file is 0, no restrictions are placed on
              the creation of hard links (i.e., this is the historical  behav-
              ior before Linux 3.6).  When the value in this file is 1, a hard
              link can be created to a target file only if one of the  follow-
              ing conditions is true:

              •  The calling process has the CAP_FOWNER capability in its user
                 namespace and the file UID has a mapping in the namespace.

              •  The filesystem UID of the process creating the  link  matches
                 the  owner  (UID) of the target file (as described in creden-
                 tials(7), a process's filesystem UID is normally the same  as
                 its effective UID).

              •  All of the following conditions are true:

                  •  the target is a regular file;

                  •  the  target  file  does not have its set-user-ID mode bit
                     enabled;

                  •  the target file does not have both its  set-group-ID  and
                     group-executable mode bits enabled; and

                  •  the  caller  has  permission to read and write the target
                     file (either via the file's permissions mask  or  because
                     it has suitable capabilities).

              The  default  value  in  this file is 0.  Setting the value to 1
              prevents a longstanding class of security issues caused by hard-
              link-based  time-of-check, time-of-use races, most commonly seen
              in world-writable directories such as /tmp.  The  common  method
              of  exploiting  this  flaw is to cross privilege boundaries when
              following a given hard link (i.e., a root process follows a hard
              link created by another user).  Additionally, on systems without
              separated partitions, this stops unauthorized users  from  "pin-
              ning"  vulnerable set-user-ID and set-group-ID files against be-
              ing upgraded by the administrator, or linking to special files.

       /proc/sys/fs/protected_regular (since Linux 4.19)
              The value in this file is/can be set to one of the following:

              0   Writing to regular files is unrestricted.

              1   Don't allow O_CREAT open(2) on regular files that the caller
                  doesn't own in world-writable sticky directories, unless the
                  regular file is owned by the owner of the directory.

              2   As for the value 1, but  the  restriction  also  applies  to
                  group-writable sticky directories.

              The  intent of the above protections is similar to protected_fi-
              fos, but allows an application to avoid writes to  an  attacker-
              controlled  regular file, where the application expected to cre-
              ate one.

       /proc/sys/fs/protected_symlinks (since Linux 3.6)
              When the value in this file is 0, no restrictions are placed  on
              following  symbolic links (i.e., this is the historical behavior
              before Linux 3.6).  When the value in this file is  1,  symbolic
              links are followed only in the following circumstances:

              •  the  filesystem UID of the process following the link matches
                 the owner (UID) of the symbolic link (as described in creden-
                 tials(7),  a process's filesystem UID is normally the same as
                 its effective UID);

              •  the link is not in a sticky world-writable directory; or

              •  the symbolic link and its  parent  directory  have  the  same
                 owner (UID)

              A  system  call  that fails to follow a symbolic link because of
              the above restrictions returns the error EACCES in errno.

              The default value in this file is 0.  Setting  the  value  to  1
              avoids a longstanding class of security issues based on time-of-
              check, time-of-use races when accessing symbolic links.

       /proc/sys/fs/suid_dumpable (since Linux 2.6.13)
              The value in this file is assigned  to  a  process's  "dumpable"
              flag in the circumstances described in prctl(2).  In effect, the
              value in this file determines whether core dump files  are  pro-
              duced  for  set-user-ID or otherwise protected/tainted binaries.
              The "dumpable" setting also affects the ownership of files in  a
              process's /proc/pid directory, as described above.

              Three different integer values can be specified:

              0 (default)
                     This  provides  the traditional (pre-Linux 2.6.13) behav-
                     ior.  A core dump will not  be  produced  for  a  process
                     which  has  changed  credentials  (by calling seteuid(2),
                     setgid(2), or similar, or by executing a  set-user-ID  or
                     set-group-ID  program) or whose binary does not have read
                     permission enabled.

              1 ("debug")
                     All processes dump core when possible.   (Reasons  why  a
                     process might nevertheless not dump core are described in
                     core(5).)  The core dump is owned by the filesystem  user
                     ID  of  the  dumping  process and no security is applied.
                     This is intended for system  debugging  situations  only:
                     this  mode  is  insecure  because  it allows unprivileged
                     users to examine the memory contents of  privileged  pro-
                     cesses.

              2 ("suidsafe")
                     Any  binary  which  normally would not be dumped (see "0"
                     above) is dumped readable by root only.  This allows  the
                     user  to  remove  the  core dump file but not to read it.
                     For security reasons core dumps in  this  mode  will  not
                     overwrite  one  another or other files.  This mode is ap-
                     propriate when administrators  are  attempting  to  debug
                     problems in a normal environment.

                     Additionally, since Linux 3.6, /proc/sys/kernel/core_pat-
                     tern must either be an absolute pathname or a  pipe  com-
                     mand,  as  detailed in core(5).  Warnings will be written
                     to the kernel log if core_pattern does not  follow  these
                     rules, and no core dump will be produced.

              For  details  of the effect of a process's "dumpable" setting on
              ptrace access mode checking, see ptrace(2).

       /proc/sys/fs/super-max
              This file controls the maximum number of superblocks,  and  thus
              the  maximum  number of mounted filesystems the kernel can have.
              You need increase only super-max  if  you  need  to  mount  more
              filesystems than the current value in super-max allows you to.

       /proc/sys/fs/super-nr
              This file contains the number of filesystems currently mounted.

       /proc/sys/kernel
              This  directory contains files controlling a range of kernel pa-
              rameters, as described below.

       /proc/sys/kernel/acct
              This file contains three numbers: highwater, lowwater, and  fre-
              quency.   If BSD-style process accounting is enabled, these val-
              ues control its behavior.  If free space on filesystem where the
              log  lives goes below lowwater percent, accounting suspends.  If
              free space gets above  highwater  percent,  accounting  resumes.
              frequency  determines  how often the kernel checks the amount of
              free space (value is in seconds).  Default values are 4, 2,  and
              30.   That  is,  suspend accounting if 2% or less space is free;
              resume it if 4% or more  space  is  free;  consider  information
              about amount of free space valid for 30 seconds.

       /proc/sys/kernel/auto_msgmni (Linux 2.6.27 to Linux 3.18)
              From  Linux  2.6.27 to Linux 3.18, this file was used to control
              recomputing of the value in /proc/sys/kernel/msgmni upon the ad-
              dition  or  removal of memory or upon IPC namespace creation/re-
              moval.  Echoing "1" into this file enabled msgmni automatic  re-
              computing  (and triggered a recomputation of msgmni based on the
              current amount of available  memory  and  number  of  IPC  name-
              spaces).   Echoing  "0"  disabled automatic recomputing.  (Auto-
              matic recomputing was also disabled if a  value  was  explicitly
              assigned  to  /proc/sys/kernel/msgmni.)   The  default  value in
              auto_msgmni was 1.

              Since Linux 3.19, the content of this file has  no  effect  (be-
              cause  msgmni  defaults to near the maximum value possible), and
              reads from this file always return the value "0".

       /proc/sys/kernel/cap_last_cap (since Linux 3.2)
              See capabilities(7).

       /proc/sys/kernel/cap-bound (from Linux 2.2 to Linux 2.6.24)
              This file holds the value of the kernel capability bounding  set
              (expressed  as  a  signed  decimal  number).   This set is ANDed
              against the capabilities  permitted  to  a  process  during  ex-
              ecve(2).  Starting with Linux 2.6.25, the system-wide capability
              bounding set disappeared,  and  was  replaced  by  a  per-thread
              bounding set; see capabilities(7).

       /proc/sys/kernel/core_pattern
              See core(5).

       /proc/sys/kernel/core_pipe_limit
              See core(5).

       /proc/sys/kernel/core_uses_pid
              See core(5).

       /proc/sys/kernel/ctrl-alt-del
              This  file  controls  the handling of Ctrl-Alt-Del from the key-
              board.  When the value  in  this  file  is  0,  Ctrl-Alt-Del  is
              trapped  and  sent  to  the init(1) program to handle a graceful
              restart.  When the value is greater than zero, Linux's  reaction
              to  a Vulcan Nerve Pinch (tm) will be an immediate reboot, with-
              out even syncing its dirty buffers.  Note: when a program  (like
              dosemu)  has the keyboard in "raw" mode, the ctrl-alt-del is in-
              tercepted by the program before it ever reaches the  kernel  tty
              layer, and it's up to the program to decide what to do with it.

       /proc/sys/kernel/dmesg_restrict (since Linux 2.6.37)
              The value in this file determines who can see kernel syslog con-
              tents.  A value of 0 in this file imposes no  restrictions.   If
              the  value  is 1, only privileged users can read the kernel sys-
              log.  (See syslog(2) for more details.)  Since Linux  3.4,  only
              users  with the CAP_SYS_ADMIN capability may change the value in
              this file.

       /proc/sys/kernel/domainname and /proc/sys/kernel/hostname
              can be used to set the NIS/YP domainname  and  the  hostname  of
              your  box  in exactly the same way as the commands domainname(1)
              and hostname(1), that is:

                  # echo 'darkstar' > /proc/sys/kernel/hostname
                  # echo 'mydomain' > /proc/sys/kernel/domainname

              has the same effect as

                  # hostname 'darkstar'
                  # domainname 'mydomain'

              Note, however, that the classic darkstar.frop.org has the  host-
              name "darkstar" and DNS (Internet Domain Name Server) domainname
              "frop.org", not to be confused with the NIS (Network Information
              Service)  or  YP  (Yellow  Pages)  domainname.  These two domain
              names are in general different.  For a detailed  discussion  see
              the hostname(1) man page.

       /proc/sys/kernel/hotplug
              This  file  contains  the pathname for the hotplug policy agent.
              The default value in this file is /sbin/hotplug.

       /proc/sys/kernel/htab-reclaim (before Linux 2.4.9.2)
              (PowerPC only) If this file is set to a nonzero value, the  Pow-
              erPC  htab  (see kernel file Documentation/powerpc/ppc_htab.txt)
              is pruned each time the system hits the idle loop.

       /proc/sys/kernel/keys/*
              This directory contains various files that define parameters and
              limits  for  the  key-management  facility.  These files are de-
              scribed in keyrings(7).

       /proc/sys/kernel/kptr_restrict (since Linux 2.6.38)
              The value in this file determines whether kernel  addresses  are
              exposed  via  /proc files and other interfaces.  A value of 0 in
              this file imposes no restrictions.  If the value  is  1,  kernel
              pointers printed using the %pK format specifier will be replaced
              with zeros unless the user has the  CAP_SYSLOG  capability.   If
              the  value  is  2,  kernel pointers printed using the %pK format
              specifier will be replaced with zeros regardless of  the  user's
              capabilities.   The  initial  default value for this file was 1,
              but the default was changed to 0 in Linux 2.6.39.   Since  Linux
              3.4, only users with the CAP_SYS_ADMIN capability can change the
              value in this file.

       /proc/sys/kernel/l2cr
              (PowerPC only) This file contains a flag that  controls  the  L2
              cache of G3 processor boards.  If 0, the cache is disabled.  En-
              abled if nonzero.

       /proc/sys/kernel/modprobe
              This file contains the pathname for the  kernel  module  loader.
              The  default  value is /sbin/modprobe.  The file is present only
              if the kernel is built with the CONFIG_MODULES  (CONFIG_KMOD  in
              Linux  2.6.26  and  earlier) option enabled.  It is described by
              the Linux kernel  source  file  Documentation/kmod.txt  (present
              only in Linux 2.4 and earlier).

       /proc/sys/kernel/modules_disabled (since Linux 2.6.31)
              A toggle value indicating if modules are allowed to be loaded in
              an otherwise modular kernel.  This toggle defaults to  off  (0),
              but  can  be  set  true  (1).  Once true, modules can be neither
              loaded nor unloaded, and the toggle cannot be set back to false.
              The  file  is  present only if the kernel is built with the CON-
              FIG_MODULES option enabled.

       /proc/sys/kernel/msgmax (since Linux 2.2)
              This file defines a system-wide  limit  specifying  the  maximum
              number  of  bytes in a single message written on a System V mes-
              sage queue.

       /proc/sys/kernel/msgmni (since Linux 2.4)
              This file defines the system-wide limit on the number of message
              queue identifiers.  See also /proc/sys/kernel/auto_msgmni.

       /proc/sys/kernel/msgmnb (since Linux 2.2)
              This file defines a system-wide parameter used to initialize the
              msg_qbytes setting for subsequently created message queues.  The
              msg_qbytes  setting  specifies  the maximum number of bytes that
              may be written to the message queue.

       /proc/sys/kernel/ngroups_max (since Linux 2.6.4)
              This is a read-only file that displays the upper  limit  on  the
              number of a process's group memberships.

       /proc/sys/kernel/ns_last_pid (since Linux 3.3)
              See pid_namespaces(7).

       /proc/sys/kernel/ostype and /proc/sys/kernel/osrelease
              These files give substrings of /proc/version.

       /proc/sys/kernel/overflowgid and /proc/sys/kernel/overflowuid
              These  files  duplicate  the  files /proc/sys/fs/overflowgid and
              /proc/sys/fs/overflowuid.

       /proc/sys/kernel/panic
              This  file  gives  read/write  access  to  the  kernel  variable
              panic_timeout.   If  this  is  zero,  the  kernel will loop on a
              panic; if nonzero, it indicates that the kernel  should  autore-
              boot  after  this  number of seconds.  When you use the software
              watchdog device driver, the recommended setting is 60.

       /proc/sys/kernel/panic_on_oops (since Linux 2.5.68)
              This file controls the kernel's behavior when an oops or BUG  is
              encountered.   If this file contains 0, then the system tries to
              continue operation.  If it contains 1, then the system delays  a
              few  seconds  (to give klogd time to record the oops output) and
              then panics.  If the /proc/sys/kernel/panic file  is  also  non-
              zero, then the machine will be rebooted.

       /proc/sys/kernel/pid_max (since Linux 2.5.34)
              This  file  specifies the value at which PIDs wrap around (i.e.,
              the value in this file is one greater  than  the  maximum  PID).
              PIDs  greater than this value are not allocated; thus, the value
              in this file also acts as a system-wide limit on the total  num-
              ber  of processes and threads.  The default value for this file,
              32768, results in the same range of PIDs as on earlier  kernels.
              On 32-bit platforms, 32768 is the maximum value for pid_max.  On
              64-bit systems, pid_max can be set  to  any  value  up  to  2^22
              (PID_MAX_LIMIT, approximately 4 million).

       /proc/sys/kernel/powersave-nap (PowerPC only)
              This file contains a flag.  If set, Linux-PPC will use the "nap"
              mode of powersaving, otherwise the "doze" mode will be used.

       /proc/sys/kernel/printk
              See syslog(2).

       /proc/sys/kernel/pty (since Linux 2.6.4)
              This directory contains two files relating to the number of UNIX
              98 pseudoterminals (see pts(4)) on the system.

       /proc/sys/kernel/pty/max
              This file defines the maximum number of pseudoterminals.

       /proc/sys/kernel/pty/nr
              This  read-only file indicates how many pseudoterminals are cur-
              rently in use.

       /proc/sys/kernel/random
              This directory contains various parameters controlling the oper-
              ation of the file /dev/random.  See random(4) for further infor-
              mation.

       /proc/sys/kernel/random/uuid (since Linux 2.4)
              Each read from this read-only file returns a randomly  generated
              128-bit UUID, as a string in the standard UUID format.

       /proc/sys/kernel/randomize_va_space (since Linux 2.6.12)
              Select  the address space layout randomization (ASLR) policy for
              the system (on architectures that support ASLR).   Three  values
              are supported for this file:

              0      Turn  ASLR  off.   This  is the default for architectures
                     that don't support ASLR, and when the  kernel  is  booted
                     with the norandmaps parameter.

              1      Make the addresses of mmap(2) allocations, the stack, and
                     the VDSO page randomized.  Among other things, this means
                     that  shared  libraries  will be loaded at randomized ad-
                     dresses.  The text segment of  PIE-linked  binaries  will
                     also  be  loaded  at a randomized address.  This value is
                     the default if the kernel was configured with CONFIG_COM-
                     PAT_BRK.

              2      (Since  Linux  2.6.25)  Also  support heap randomization.
                     This value is the default if the kernel was  not  config-
                     ured with CONFIG_COMPAT_BRK.

       /proc/sys/kernel/real-root-dev
              This file is documented in the Linux kernel source file Documen-
              tation/admin-guide/initrd.rst (or  Documentation/initrd.txt  be-
              fore Linux 4.10).

       /proc/sys/kernel/reboot-cmd (Sparc only)
              This  file  seems  to  be a way to give an argument to the SPARC
              ROM/Flash boot loader.  Maybe to tell it what to  do  after  re-
              booting?

       /proc/sys/kernel/rtsig-max
              (Up  to  and  including Linux 2.6.7; see setrlimit(2)) This file
              can be used to  tune  the  maximum  number  of  POSIX  real-time
              (queued) signals that can be outstanding in the system.

       /proc/sys/kernel/rtsig-nr
              (Up  to  and including Linux 2.6.7.)  This file shows the number
              of POSIX real-time signals currently queued.

       /proc/pid/sched_autogroup_enabled (since Linux 2.6.38)
              See sched(7).

       /proc/sys/kernel/sched_child_runs_first (since Linux 2.6.23)
              If this file contains the value zero, then, after a fork(2), the
              parent  is  first  scheduled on the CPU.  If the file contains a
              nonzero value, then the child is scheduled  first  on  the  CPU.
              (Of course, on a multiprocessor system, the parent and the child
              might both immediately be scheduled on a CPU.)

       /proc/sys/kernel/sched_rr_timeslice_ms (since Linux 3.9)
              See sched_rr_get_interval(2).

       /proc/sys/kernel/sched_rt_period_us (since Linux 2.6.25)
              See sched(7).

       /proc/sys/kernel/sched_rt_runtime_us (since Linux 2.6.25)
              See sched(7).

       /proc/sys/kernel/seccomp (since Linux 4.14)
              This directory provides additional seccomp information and  con-
              figuration.  See seccomp(2) for further details.

       /proc/sys/kernel/sem (since Linux 2.4)
              This  file  contains  4 numbers defining limits for System V IPC
              semaphores.  These fields are, in order:

              SEMMSL The maximum semaphores per semaphore set.

              SEMMNS A system-wide limit on the number of  semaphores  in  all
                     semaphore sets.

              SEMOPM The maximum number of operations that may be specified in
                     a semop(2) call.

              SEMMNI A system-wide limit on the maximum  number  of  semaphore
                     identifiers.

       /proc/sys/kernel/sg-big-buff
              This file shows the size of the generic SCSI device (sg) buffer.
              You can't tune it just yet, but you could change it  at  compile
              time  by  editing  include/scsi/sg.h  and  changing the value of
              SG_BIG_BUFF.  However, there shouldn't be any reason  to  change
              this value.

       /proc/sys/kernel/shm_rmid_forced (since Linux 3.1)
              If  this  file  is set to 1, all System V shared memory segments
              will be marked for destruction as soon as the number of attached
              processes  falls to zero; in other words, it is no longer possi-
              ble to create shared memory segments that exist independently of
              any attached process.

              The effect is as though a shmctl(2) IPC_RMID is performed on all
              existing segments as well as all segments created in the  future
              (until  this  file  is reset to 0).  Note that existing segments
              that are attached to no process will  be  immediately  destroyed
              when  this  file is set to 1.  Setting this option will also de-
              stroy segments that were created, but never attached, upon  ter-
              mination of the process that created the segment with shmget(2).

              Setting  this file to 1 provides a way of ensuring that all Sys-
              tem V shared memory segments are counted  against  the  resource
              usage  and  resource limits (see the description of RLIMIT_AS in
              getrlimit(2)) of at least one process.

              Because setting this file to 1 produces behavior  that  is  non-
              standard and could also break existing applications, the default
              value in this file is 0.  Set this file to 1 only if you have  a
              good  understanding  of  the semantics of the applications using
              System V shared memory on your system.

       /proc/sys/kernel/shmall (since Linux 2.2)
              This file contains the system-wide limit on the total number  of
              pages of System V shared memory.

       /proc/sys/kernel/shmmax (since Linux 2.2)
              This file can be used to query and set the run-time limit on the
              maximum (System V IPC) shared memory segment size  that  can  be
              created.  Shared memory segments up to 1 GB are now supported in
              the kernel.  This value defaults to SHMMAX.

       /proc/sys/kernel/shmmni (since Linux 2.4)
              This file specifies the system-wide maximum number of  System  V
              shared memory segments that can be created.

       /proc/sys/kernel/sysctl_writes_strict (since Linux 3.16)
              The  value  in  this file determines how the file offset affects
              the behavior of updating entries in files under /proc/sys.   The
              file has three possible values:

              -1  This  provides  legacy  handling,  with  no printk warnings.
                  Each write(2) must fully contain the value  to  be  written,
                  and  multiple  writes on the same file descriptor will over-
                  write the entire value, regardless of the file position.

              0   (default) This provides the same behavior  as  for  -1,  but
                  printk  warnings  are  written  for  processes  that perform
                  writes when the file offset is not 0.

              1   Respect the file offset when writing strings into  /proc/sys
                  files.   Multiple  writes  will  append to the value buffer.
                  Anything written beyond the maximum length of the value buf-
                  fer  will  be  ignored.  Writes to numeric /proc/sys entries
                  must always be at file offset 0 and the value must be  fully
                  contained in the buffer provided to write(2).

       /proc/sys/kernel/sysrq
              This  file  controls  the functions allowed to be invoked by the
              SysRq key.  By default, the file contains 1 meaning  that  every
              possible  SysRq  request  is  allowed (in older kernel versions,
              SysRq was disabled by default, and you were required to specifi-
              cally enable it at run-time, but this is not the case any more).
              Possible values in this file are:

              0    Disable sysrq completely

              1    Enable all functions of sysrq

              > 1  Bit mask of allowed sysrq functions, as follows:
                     2  Enable control of console logging level
                     4  Enable control of keyboard (SAK, unraw)
                     8  Enable debugging dumps of processes etc.
                    16  Enable sync command
                    32  Enable remount read-only
                    64  Enable signaling of processes (term, kill, oom-kill)
                   128  Allow reboot/poweroff
                   256  Allow nicing of all real-time tasks

              This file is present only if the CONFIG_MAGIC_SYSRQ kernel  con-
              figuration option is enabled.  For further details see the Linux
              kernel source file Documentation/admin-guide/sysrq.rst (or Docu-
              mentation/sysrq.txt before Linux 4.10).

       /proc/sys/kernel/version
              This file contains a string such as:

                  #5 Wed Feb 25 21:49:24 MET 1998

              The  "#5"  means  that  this is the fifth kernel built from this
              source base and the date following it  indicates  the  time  the
              kernel was built.

       /proc/sys/kernel/threads-max (since Linux 2.3.11)
              This  file  specifies  the  system-wide  limit  on the number of
              threads (tasks) that can be created on the system.

              Since Linux 4.1, the value that can be written to threads-max is
              bounded.  The minimum value that can be written is 20.  The max-
              imum value that can be written is  given  by  the  constant  FU-
              TEX_TID_MASK  (0x3fffffff).  If a value outside of this range is
              written to threads-max, the error EINVAL occurs.

              The value written is checked against the  available  RAM  pages.
              If the thread structures would occupy too much (more than 1/8th)
              of the available RAM pages, threads-max is reduced accordingly.

       /proc/sys/kernel/yama/ptrace_scope (since Linux 3.5)
              See ptrace(2).

       /proc/sys/kernel/zero-paged (PowerPC only)
              This file contains a flag.  When  enabled  (nonzero),  Linux-PPC
              will  pre-zero  pages  in  the  idle  loop, possibly speeding up
              get_free_pages.

       /proc/sys/net
              This directory contains networking stuff.  Explanations for some
              of  the  files  under  this directory can be found in tcp(7) and
              ip(7).

       /proc/sys/net/core/bpf_jit_enable
              See bpf(2).

       /proc/sys/net/core/somaxconn
              This file defines a ceiling value for the  backlog  argument  of
              listen(2); see the listen(2) manual page for details.

       /proc/sys/proc
              This directory may be empty.

       /proc/sys/sunrpc
              This  directory  supports  Sun remote procedure call for network
              filesystem (NFS).  On some systems, it is not present.

       /proc/sys/user (since Linux 4.9)
              See namespaces(7).

       /proc/sys/vm
              This directory contains files for memory management tuning, buf-
              fer, and cache management.

       /proc/sys/vm/admin_reserve_kbytes (since Linux 3.10)
              This file defines the amount of free memory (in KiB) on the sys-
              tem that should  be  reserved  for  users  with  the  capability
              CAP_SYS_ADMIN.

              The  default  value  in  this file is the minimum of [3% of free
              pages, 8MiB] expressed as KiB.  The default is intended to  pro-
              vide  enough  for the superuser to log in and kill a process, if
              necessary, under the default overcommit 'guess' mode (i.e., 0 in
              /proc/sys/vm/overcommit_memory).

              Systems   running   in  "overcommit  never"  mode  (i.e.,  2  in
              /proc/sys/vm/overcommit_memory) should  increase  the  value  in
              this  file  to  account  for the full virtual memory size of the
              programs used to recover (e.g.,  login(1)  ssh(1),  and  top(1))
              Otherwise,  the  superuser  may not be able to log in to recover
              the system.  For example, on x86-64 a suitable value  is  131072
              (128MiB reserved).

              Changing  the value in this file takes effect whenever an appli-
              cation requests memory.

       /proc/sys/vm/compact_memory (since Linux 2.6.35)
              When 1 is written to this file, all  zones  are  compacted  such
              that  free memory is available in contiguous blocks where possi-
              ble.  The effect  of  this  action  can  be  seen  by  examining
              /proc/buddyinfo.

              Present  only  if  the  kernel  was  configured with CONFIG_COM-
              PACTION.

       /proc/sys/vm/drop_caches (since Linux 2.6.16)
              Writing to this file causes the kernel  to  drop  clean  caches,
              dentries,  and inodes from memory, causing that memory to become
              free.  This can be useful for memory management testing and per-
              forming  reproducible filesystem benchmarks.  Because writing to
              this file causes the benefits of caching to be lost, it can  de-
              grade overall system performance.

              To free pagecache, use:

                  echo 1 > /proc/sys/vm/drop_caches

              To free dentries and inodes, use:

                  echo 2 > /proc/sys/vm/drop_caches

              To free pagecache, dentries, and inodes, use:

                  echo 3 > /proc/sys/vm/drop_caches

              Because  writing  to this file is a nondestructive operation and
              dirty objects are not freeable,  the  user  should  run  sync(1)
              first.

       /proc/sys/vm/sysctl_hugetlb_shm_group (since Linux 2.6.7)
              This  writable file contains a group ID that is allowed to allo-
              cate memory using huge pages.  If a  process  has  a  filesystem
              group  ID  or any supplementary group ID that matches this group
              ID, then it can make huge-page allocations without  holding  the
              CAP_IPC_LOCK   capability;  see  memfd_create(2),  mmap(2),  and
              shmget(2).

       /proc/sys/vm/legacy_va_layout (since Linux 2.6.9)
              If nonzero, this disables the new 32-bit memory-mapping  layout;
              the kernel will use the legacy (2.4) layout for all processes.

       /proc/sys/vm/memory_failure_early_kill (since Linux 2.6.32)
              Control  how  to kill processes when an uncorrected memory error
              (typically a 2-bit error in a memory module) that cannot be han-
              dled  by  the  kernel is detected in the background by hardware.
              In some cases (like the page still having a valid copy on disk),
              the kernel will handle the failure transparently without affect-
              ing any applications.  But if there is no other up-to-date  copy
              of  the data, it will kill processes to prevent any data corrup-
              tions from propagating.

              The file has one of the following values:

              1      Kill  all  processes  that  have  the  corrupted-and-not-
                     reloadable  page  mapped as soon as the corruption is de-
                     tected.  Note that this is not supported for a few  types
                     of pages, such as kernel internally allocated data or the
                     swap cache, but works for the majority of user pages.

              0      Unmap the corrupted page from all processes  and  kill  a
                     process only if it tries to access the page.

              The  kill is performed using a SIGBUS signal with si_code set to
              BUS_MCEERR_AO.  Processes can handle this if they want  to;  see
              sigaction(2) for more details.

              This  feature is active only on architectures/platforms with ad-
              vanced machine check handling and depends on the hardware  capa-
              bilities.

              Applications  can override the memory_failure_early_kill setting
              individually with the prctl(2) PR_MCE_KILL operation.

              Present only if  the  kernel  was  configured  with  CONFIG_MEM-
              ORY_FAILURE.

       /proc/sys/vm/memory_failure_recovery (since Linux 2.6.32)
              Enable memory failure recovery (when supported by the platform).

              1      Attempt recovery.

              0      Always panic on a memory failure.

              Present  only  if  the  kernel  was  configured with CONFIG_MEM-
              ORY_FAILURE.

       /proc/sys/vm/oom_dump_tasks (since Linux 2.6.25)
              Enables a system-wide task dump (excluding kernel threads) to be
              produced  when the kernel performs an OOM-killing.  The dump in-
              cludes  the  following  information  for  each   task   (thread,
              process): thread ID, real user ID, thread group ID (process ID),
              virtual memory size, resident set size, the CPU that the task is
              scheduled   on,   oom_adj   score   (see   the   description  of
              /proc/pid/oom_adj), and command name.  This is helpful to deter-
              mine  why  the  OOM-killer was invoked and to identify the rogue
              task that caused it.

              If this contains the value zero, this information is suppressed.
              On  very  large  systems  with thousands of tasks, it may not be
              feasible to dump the memory  state  information  for  each  one.
              Such systems should not be forced to incur a performance penalty
              in OOM situations when the information may not be desired.

              If this is set to nonzero, this information  is  shown  whenever
              the OOM-killer actually kills a memory-hogging task.

              The default value is 0.

       /proc/sys/vm/oom_kill_allocating_task (since Linux 2.6.24)
              This enables or disables killing the OOM-triggering task in out-
              of-memory situations.

              If this is set to zero, the OOM-killer will scan through the en-
              tire  tasklist  and  select  a task based on heuristics to kill.
              This normally selects a rogue memory-hogging task that frees  up
              a large amount of memory when killed.

              If  this is set to nonzero, the OOM-killer simply kills the task
              that triggered the out-of-memory condition.  This avoids a  pos-
              sibly expensive tasklist scan.

              If  /proc/sys/vm/panic_on_oom  is  nonzero,  it takes precedence
              over whatever value is  used  in  /proc/sys/vm/oom_kill_allocat-
              ing_task.

              The default value is 0.

       /proc/sys/vm/overcommit_kbytes (since Linux 3.14)
              This writable file provides an alternative to /proc/sys/vm/over-
              commit_ratio    for    controlling    the    CommitLimit    when
              /proc/sys/vm/overcommit_memory  has  the value 2.  It allows the
              amount of memory overcommitting to be specified as  an  absolute
              value  (in  kB),  rather  than  as a percentage, as is done with
              overcommit_ratio.  This allows for finer-grained control of Com-
              mitLimit on systems with extremely large memory sizes.

              Only  one  of  overcommit_kbytes or overcommit_ratio can have an
              effect: if overcommit_kbytes has a nonzero  value,  then  it  is
              used  to  calculate  CommitLimit,  otherwise overcommit_ratio is
              used.  Writing a value to either of these files causes the value
              in the other file to be set to zero.

       /proc/sys/vm/overcommit_memory
              This  file  contains  the kernel virtual memory accounting mode.
              Values are:

                     0: heuristic overcommit (this is the default)
                     1: always overcommit, never check
                     2: always check, never overcommit

              In mode 0, calls of mmap(2) with MAP_NORESERVE are not  checked,
              and  the default check is very weak, leading to the risk of get-
              ting a process "OOM-killed".

              In mode 1, the kernel pretends there is  always  enough  memory,
              until  memory  actually runs out.  One use case for this mode is
              scientific computing applications that employ large  sparse  ar-
              rays.  Before Linux 2.6.0, any nonzero value implies mode 1.

              In mode 2 (available since Linux 2.6), the total virtual address
              space that can be allocated (CommitLimit  in  /proc/meminfo)  is
              calculated as

                  CommitLimit = (total_RAM - total_huge_TLB) *
                          overcommit_ratio / 100 + total_swap

              where:

              •  total_RAM is the total amount of RAM on the system;

              •  total_huge_TLB  is  the  amount  of memory set aside for huge
                 pages;

              •  overcommit_ratio is the value in  /proc/sys/vm/overcommit_ra-
                 tio; and

              •  total_swap is the amount of swap space.

              For  example,  on  a system with 16 GB of physical RAM, 16 GB of
              swap, no space dedicated to huge pages, and an  overcommit_ratio
              of 50, this formula yields a CommitLimit of 24 GB.

              Since Linux 3.14, if the value in /proc/sys/vm/overcommit_kbytes
              is nonzero, then CommitLimit is instead calculated as:

                  CommitLimit = overcommit_kbytes + total_swap

              See also the  description  of  /proc/sys/vm/admin_reserve_kbytes
              and /proc/sys/vm/user_reserve_kbytes.

       /proc/sys/vm/overcommit_ratio (since Linux 2.6.0)
              This  writable  file defines a percentage by which memory can be
              overcommitted.  The default value in the file is  50.   See  the
              description of /proc/sys/vm/overcommit_memory.

       /proc/sys/vm/panic_on_oom (since Linux 2.6.18)
              This enables or disables a kernel panic in an out-of-memory sit-
              uation.

              If this file is set to the value 0, the kernel's OOM-killer will
              kill  some  rogue  process.   Usually, the OOM-killer is able to
              kill a rogue process and the system will survive.

              If this file is set to the value 1,  then  the  kernel  normally
              panics when out-of-memory happens.  However, if a process limits
              allocations to certain nodes  using  memory  policies  (mbind(2)
              MPOL_BIND)  or  cpusets (cpuset(7)) and those nodes reach memory
              exhaustion status, one process may be killed by the  OOM-killer.
              No panic occurs in this case: because other nodes' memory may be
              free, this means the system as a whole may not have  reached  an
              out-of-memory situation yet.

              If  this  file  is  set to the value 2, the kernel always panics
              when an out-of-memory condition occurs.

              The default value is 0.  1 and 2 are for failover of clustering.
              Select either according to your policy of failover.

       /proc/sys/vm/swappiness
              The value in this file controls how aggressively the kernel will
              swap memory pages.  Higher values increase aggressiveness, lower
              values decrease aggressiveness.  The default value is 60.

       /proc/sys/vm/user_reserve_kbytes (since Linux 3.10)
              Specifies  an amount of memory (in KiB) to reserve for user pro-
              cesses.  This is intended to prevent a user from starting a sin-
              gle  memory hogging process, such that they cannot recover (kill
              the hog).  The value in  this  file  has  an  effect  only  when
              /proc/sys/vm/overcommit_memory  is  set to 2 ("overcommit never"
              mode).  In this case, the system reserves an  amount  of  memory
              that  is  the  minimum  of [3% of current process size, user_re-
              serve_kbytes].

              The default value in this file is the minimum  of  [3%  of  free
              pages, 128MiB] expressed as KiB.

              If  the  value  in this file is set to zero, then a user will be
              allowed to allocate all free memory with a single process (minus
              the  amount reserved by /proc/sys/vm/admin_reserve_kbytes).  Any
              subsequent attempts to execute a command will result  in  "fork:
              Cannot allocate memory".

              Changing  the value in this file takes effect whenever an appli-
              cation requests memory.

       /proc/sys/vm/unprivileged_userfaultfd (since Linux 5.2)
              This (writable) file exposes a flag that  controls  whether  un-
              privileged  processes  are allowed to employ userfaultfd(2).  If
              this file has the value 1, then unprivileged processes  may  use
              userfaultfd(2).   If  this  file has the value 0, then only pro-
              cesses that have the CAP_SYS_PTRACE capability may employ  user-
              faultfd(2).  The default value in this file is 1.

       /proc/sysrq-trigger (since Linux 2.4.21)
              Writing  a  character to this file triggers the same SysRq func-
              tion as typing ALT-SysRq-<character>  (see  the  description  of
              /proc/sys/kernel/sysrq).  This file is normally writable only by
              root.  For further details see the Linux kernel source file Doc-
              umentation/admin-guide/sysrq.rst (or Documentation/sysrq.txt be-
              fore Linux 4.10).

       /proc/sysvipc
              Subdirectory containing  the  pseudo-files  msg,  sem  and  shm.
              These  files  list the System V Interprocess Communication (IPC)
              objects (respectively: message queues,  semaphores,  and  shared
              memory)  that  currently  exist on the system, providing similar
              information to that available via  ipcs(1).   These  files  have
              headers and are formatted (one IPC object per line) for easy un-
              derstanding.  sysvipc(7) provides further background on the  in-
              formation shown by these files.

       /proc/thread-self (since Linux 3.17)
              This directory refers to the thread accessing the /proc filesys-
              tem, and is identical to the /proc/self/task/tid directory named
              by the process thread ID (tid) of the same thread.

       /proc/timer_list (since Linux 2.6.21)
              This  read-only  file  exposes  a  list of all currently pending
              (high-resolution) timers, all clock-event sources, and their pa-
              rameters in a human-readable form.

       /proc/timer_stats (from  Linux 2.6.21 until Linux 4.10)
              This  is  a  debugging facility to make timer (ab)use in a Linux
              system visible to kernel and user-space developers.  It  can  be
              used  by  kernel  and user-space developers to verify that their
              code does not make undue use of timers.  The goal  is  to  avoid
              unnecessary wakeups, thereby optimizing power consumption.

              If  enabled in the kernel (CONFIG_TIMER_STATS), but not used, it
              has almost zero run-time overhead and a relatively  small  data-
              structure  overhead.  Even if collection is enabled at run time,
              overhead is low: all  the  locking  is  per-CPU  and  lookup  is
              hashed.

              The  /proc/timer_stats file is used both to control sampling fa-
              cility and to read out the sampled information.

              The timer_stats functionality is inactive on bootup.  A sampling
              period can be started using the following command:

                  # echo 1 > /proc/timer_stats

              The following command stops a sampling period:

                  # echo 0 > /proc/timer_stats

              The statistics can be retrieved by:

                  $ cat /proc/timer_stats

              While  sampling  is enabled, each readout from /proc/timer_stats
              will see newly updated statistics.  Once sampling  is  disabled,
              the  sampled  information  is  kept until a new sample period is
              started.  This allows multiple readouts.

              Sample output from /proc/timer_stats:

                  $ cat /proc/timer_stats
                  Timer Stats Version: v0.3
                  Sample period: 1.764 s
                  Collection: active
                    255,     0 swapper/3        hrtimer_start_range_ns (tick_sched_timer)
                     71,     0 swapper/1        hrtimer_start_range_ns (tick_sched_timer)
                     58,     0 swapper/0        hrtimer_start_range_ns (tick_sched_timer)
                      4,  1694 gnome-shell      mod_delayed_work_on (delayed_work_timer_fn)
                     17,     7 rcu_sched        rcu_gp_kthread (process_timeout)
                  ...
                      1,  4911 kworker/u16:0    mod_delayed_work_on (delayed_work_timer_fn)
                     1D,  2522 kworker/0:0      queue_delayed_work_on (delayed_work_timer_fn)
                  1029 total events, 583.333 events/sec

              The output columns are:

              [1]  a count of the number of events,  optionally  (since  Linux
                   2.6.23)  followed by the letter 'D' if this is a deferrable
                   timer;

              [2]  the PID of the process that initialized the timer;

              [3]  the name of the process that initialized the timer;

              [4]  the function where  the  timer  was  initialized;  and  (in
                   parentheses)  the callback function that is associated with
                   the timer.

              During the Linux 4.11 development cycle, this file  was  removed
              because  of  security concerns, as it exposes information across
              namespaces.  Furthermore, it is possible to obtain the same  in-
              formation via in-kernel tracing facilities such as ftrace.

       /proc/tty
              Subdirectory  containing the pseudo-files and subdirectories for
              tty drivers and line disciplines.

       /proc/uptime
              This file contains two numbers (values in seconds):  the  uptime
              of  the  system (including time spent in suspend) and the amount
              of time spent in the idle process.

       /proc/version
              This string identifies the kernel version that is currently run-
              ning.   It  includes  the  contents  of /proc/sys/kernel/ostype,
              /proc/sys/kernel/osrelease, and  /proc/sys/kernel/version.   For
              example:

                  Linux version 1.0.9 (quinlan@phaze) #1 Sat May 14 01:51:54 EDT 1994

       /proc/vmstat (since Linux 2.6.0)
              This file displays various virtual memory statistics.  Each line
              of this file contains a single  name-value  pair,  delimited  by
              white space.  Some lines are present only if the kernel was con-
              figured with suitable options.  (In some cases, the options  re-
              quired for particular files have changed across kernel versions,
              so they are not listed here.  Details can be found by consulting
              the kernel source code.)  The following fields may be present:

              nr_free_pages (since Linux 2.6.31)

              nr_alloc_batch (since Linux 3.12)

              nr_inactive_anon (since Linux 2.6.28)

              nr_active_anon (since Linux 2.6.28)

              nr_inactive_file (since Linux 2.6.28)

              nr_active_file (since Linux 2.6.28)

              nr_unevictable (since Linux 2.6.28)

              nr_mlock (since Linux 2.6.28)

              nr_anon_pages (since Linux 2.6.18)

              nr_mapped (since Linux 2.6.0)

              nr_file_pages (since Linux 2.6.18)

              nr_dirty (since Linux 2.6.0)

              nr_writeback (since Linux 2.6.0)

              nr_slab_reclaimable (since Linux 2.6.19)

              nr_slab_unreclaimable (since Linux 2.6.19)

              nr_page_table_pages (since Linux 2.6.0)

              nr_kernel_stack (since Linux 2.6.32)
                     Amount of memory allocated to kernel stacks.

              nr_unstable (since Linux 2.6.0)

              nr_bounce (since Linux 2.6.12)

              nr_vmscan_write (since Linux 2.6.19)

              nr_vmscan_immediate_reclaim (since Linux 3.2)

              nr_writeback_temp (since Linux 2.6.26)

              nr_isolated_anon (since Linux 2.6.32)

              nr_isolated_file (since Linux 2.6.32)

              nr_shmem (since Linux 2.6.32)
                     Pages used by shmem and tmpfs(5).

              nr_dirtied (since Linux 2.6.37)

              nr_written (since Linux 2.6.37)

              nr_pages_scanned (since Linux 3.17)

              numa_hit (since Linux 2.6.18)

              numa_miss (since Linux 2.6.18)

              numa_foreign (since Linux 2.6.18)

              numa_interleave (since Linux 2.6.18)

              numa_local (since Linux 2.6.18)

              numa_other (since Linux 2.6.18)

              workingset_refault (since Linux 3.15)

              workingset_activate (since Linux 3.15)

              workingset_nodereclaim (since Linux 3.15)

              nr_anon_transparent_hugepages (since Linux 2.6.38)

              nr_free_cma (since Linux 3.7)
                     Number of free CMA (Contiguous Memory Allocator) pages.

              nr_dirty_threshold (since Linux 2.6.37)

              nr_dirty_background_threshold (since Linux 2.6.37)

              pgpgin (since Linux 2.6.0)

              pgpgout (since Linux 2.6.0)

              pswpin (since Linux 2.6.0)

              pswpout (since Linux 2.6.0)

              pgalloc_dma (since Linux 2.6.5)

              pgalloc_dma32 (since Linux 2.6.16)

              pgalloc_normal (since Linux 2.6.5)

              pgalloc_high (since Linux 2.6.5)

              pgalloc_movable (since Linux 2.6.23)

              pgfree (since Linux 2.6.0)

              pgactivate (since Linux 2.6.0)

              pgdeactivate (since Linux 2.6.0)

              pgfault (since Linux 2.6.0)

              pgmajfault (since Linux 2.6.0)

              pgrefill_dma (since Linux 2.6.5)

              pgrefill_dma32 (since Linux 2.6.16)

              pgrefill_normal (since Linux 2.6.5)

              pgrefill_high (since Linux 2.6.5)

              pgrefill_movable (since Linux 2.6.23)

              pgsteal_kswapd_dma (since Linux 3.4)

              pgsteal_kswapd_dma32 (since Linux 3.4)

              pgsteal_kswapd_normal (since Linux 3.4)

              pgsteal_kswapd_high (since Linux 3.4)

              pgsteal_kswapd_movable (since Linux 3.4)

              pgsteal_direct_dma

              pgsteal_direct_dma32 (since Linux 3.4)

              pgsteal_direct_normal (since Linux 3.4)

              pgsteal_direct_high (since Linux 3.4)

              pgsteal_direct_movable (since Linux 2.6.23)

              pgscan_kswapd_dma

              pgscan_kswapd_dma32 (since Linux 2.6.16)

              pgscan_kswapd_normal (since Linux 2.6.5)

              pgscan_kswapd_high

              pgscan_kswapd_movable (since Linux 2.6.23)

              pgscan_direct_dma

              pgscan_direct_dma32 (since Linux 2.6.16)

              pgscan_direct_normal

              pgscan_direct_high

              pgscan_direct_movable (since Linux 2.6.23)

              pgscan_direct_throttle (since Linux 3.6)

              zone_reclaim_failed (since linux 2.6.31)

              pginodesteal (since linux 2.6.0)

              slabs_scanned (since linux 2.6.5)

              kswapd_inodesteal (since linux 2.6.0)

              kswapd_low_wmark_hit_quickly (since Linux 2.6.33)

              kswapd_high_wmark_hit_quickly (since Linux 2.6.33)

              pageoutrun (since Linux 2.6.0)

              allocstall (since Linux 2.6.0)

              pgrotated (since Linux 2.6.0)

              drop_pagecache (since Linux 3.15)

              drop_slab (since Linux 3.15)

              numa_pte_updates (since Linux 3.8)

              numa_huge_pte_updates (since Linux 3.13)

              numa_hint_faults (since Linux 3.8)

              numa_hint_faults_local (since Linux 3.8)

              numa_pages_migrated (since Linux 3.8)

              pgmigrate_success (since Linux 3.8)

              pgmigrate_fail (since Linux 3.8)

              compact_migrate_scanned (since Linux 3.8)

              compact_free_scanned (since Linux 3.8)

              compact_isolated (since Linux 3.8)

              compact_stall (since Linux 2.6.35)
                     See    the    kernel    source   file   Documentation/ad-
                     min-guide/mm/transhuge.rst.

              compact_fail (since Linux 2.6.35)
                     See   the   kernel    source    file    Documentation/ad-
                     min-guide/mm/transhuge.rst.

              compact_success (since Linux 2.6.35)
                     See    the    kernel    source   file   Documentation/ad-
                     min-guide/mm/transhuge.rst.

              htlb_buddy_alloc_success (since Linux 2.6.26)

              htlb_buddy_alloc_fail (since Linux 2.6.26)

              unevictable_pgs_culled (since Linux 2.6.28)

              unevictable_pgs_scanned (since Linux 2.6.28)

              unevictable_pgs_rescued (since Linux 2.6.28)

              unevictable_pgs_mlocked (since Linux 2.6.28)

              unevictable_pgs_munlocked (since Linux 2.6.28)

              unevictable_pgs_cleared (since Linux 2.6.28)

              unevictable_pgs_stranded (since Linux 2.6.28)

              thp_fault_alloc (since Linux 2.6.39)
                     See   the   kernel    source    file    Documentation/ad-
                     min-guide/mm/transhuge.rst.

              thp_fault_fallback (since Linux 2.6.39)
                     See    the    kernel    source   file   Documentation/ad-
                     min-guide/mm/transhuge.rst.

              thp_collapse_alloc (since Linux 2.6.39)
                     See   the   kernel    source    file    Documentation/ad-
                     min-guide/mm/transhuge.rst.

              thp_collapse_alloc_failed (since Linux 2.6.39)
                     See    the    kernel    source   file   Documentation/ad-
                     min-guide/mm/transhuge.rst.

              thp_split (since Linux 2.6.39)
                     See   the   kernel    source    file    Documentation/ad-
                     min-guide/mm/transhuge.rst.

              thp_zero_page_alloc (since Linux 3.8)
                     See    the    kernel    source   file   Documentation/ad-
                     min-guide/mm/transhuge.rst.

              thp_zero_page_alloc_failed (since Linux 3.8)
                     See   the   kernel    source    file    Documentation/ad-
                     min-guide/mm/transhuge.rst.

              balloon_inflate (since Linux 3.18)

              balloon_deflate (since Linux 3.18)

              balloon_migrate (since Linux 3.18)

              nr_tlb_remote_flush (since Linux 3.12)

              nr_tlb_remote_flush_received (since Linux 3.12)

              nr_tlb_local_flush_all (since Linux 3.12)

              nr_tlb_local_flush_one (since Linux 3.12)

              vmacache_find_calls (since Linux 3.16)

              vmacache_find_hits (since Linux 3.16)

              vmacache_full_flushes (since Linux 3.19)

       /proc/zoneinfo (since Linux 2.6.13)
              This file displays information about memory zones.  This is use-
              ful for analyzing virtual memory behavior.

NOTES
       Many files contain strings (e.g., the  environment  and  command  line)
       that  are  in  the  internal  format, with subfields terminated by null
       bytes ('\0').  When inspecting such files, you may find  that  the  re-
       sults  are  more readable if you use a command of the following form to
       display them:

           $ cat file | tr '\000' '\n'

       This manual page is incomplete, possibly inaccurate, and is the kind of
       thing that needs to be updated very often.

SEE ALSO
       cat(1), dmesg(1), find(1), free(1), htop(1), init(1), ps(1), pstree(1),
       tr(1),   uptime(1),   chroot(2),   mmap(2),   readlink(2),   syslog(2),
       slabinfo(5),  sysfs(5),  hier(7),  namespaces(7),  time(7), arp(8), hd-
       parm(8),  ifconfig(8),  lsmod(8),   lspci(8),   mount(8),   netstat(8),
       procinfo(8), route(8), sysctl(8)

       The Linux kernel source files: Documentation/filesystems/proc.rst, Doc-
       umentation/admin-guide/sysctl/fs.rst,                 Documentation/ad-
       min-guide/sysctl/kernel.rst,  Documentation/admin-guide/sysctl/net.rst,
       and Documentation/admin-guide/sysctl/vm.rst.

Linux man-pages 6.03              2023-02-10                           proc(5)

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