DOTLOCKFILE(1) Cistron Utilities DOTLOCKFILE(1)
NAME
dotlockfile - Utility to manage lockfiles
SYNOPSIS
dotlockfile -l [-r retries] [-i interval] [-p] [-q] <-m | lockfile>
dotlockfile -l [-r retries] [-i interval] [-p] [-q] <-m | lockfile>
[-P] cmd args ...
dotlockfile -u | -t
DESCRIPTION
dotlockfile is a command line utility to reliably create, test and re-
move lockfiles. It creates lockfiles reliably on local and NFS
filesystems, because the crucial steps of testing for a preexisting
lockfile and creating it are performed atomically by a single call to
link(2). Manpage lockfile_create(3) describes the used algorithm.
dotlockfile is installed with attribute SETGID mail and thus can also
be used to lock and unlock mailboxes even if the mailspool directory is
only writable by group mail.
The name dotlockfile comes from the way mailboxes are locked for up-
dates on a lot of UNIX systems. A lockfile is created with the same
filename as the mailbox but with the string ".lock" appended.
The names dotlock and lockfile were already taken – hence the name dot-
lockfile :).
OPTIONS
-l Create a lockfile if no preexisting valid lockfile is found,
else wait and retry according to option -r. Retry interval can
be explicitly set with option -i. This option (-l) is the de-
fault, so it can be left off.
A lockfile is treated as valid,
• if it holds the process-id of a running process,
• or if it does not hold any process-id and has been touched
less than 5 minutes ago (timestamp is younger than 5 minutes).
-r retries
The number of times dotlockfile retries to acquire the lock if
it failed the first time before giving up. The initial sleep
after failing to acquire the lock is 5 seconds. After each
retry the sleep interval is increased incrementally by 5 seconds
up to a maximum sleep of 60 seconds between tries unless over-
ridden by -i. The default number of retries is 5. To try only
once, use "-r 0". To try indefinitely, use "-r -1".
-i interval
Sets a consistent retry interval.
-u Remove a lockfile.
-t Touch an existing lockfile (update the timestamp). Useful for
lockfiles on NFS filesystems. For lockfiles on local filesys-
tems the -p option is preferable.
-p Write the process-id of the calling process (or dotlockfile it-
self if a command is executed) into the lockfile. Also when
testing for an existing lockfile, check the contents for the
process-id of a running process to verify if the lockfile is
still valid. Obviously useful only for lockfiles on local
filesystems.
-m Lock or unlock the current users mailbox. The path to the mail-
box is the default system mailspool directory (usually
/var/mail) with the username as gotten from getpwuid() appended.
If the environment variable $MAIL is set, that is used instead.
Then the string ".lock" is appended to get the name of the ac-
tual lockfile.
-q Don't print warnings or errors to the standard error output.
Used internally by liblockfile when it spawns dotlockfile as a
helper program.
-P On successful "lock and spawn command", don't exit with status
zero, but pass through the exit value of the spawned command.
lockfile
The lockfile to be created or removed. Must not be specified if
the -m option is given.
command argument ...
Create lockfile, run the command , wait for it to exit, and re-
move lockfile.
RETURN VALUE
Zero on success, and non-zero on failure. When locking (the default,
or with the -l option) dotlockfile returns the same values as the li-
brary function lockfile_create(3). Unlocking a non-existent lockfile
is not an error.
Unless the -P option was supplied, when a command is executed, the re-
turn value does not correspond with that of the command that was run.
If locking and unlocking was successful, the exit status is zero.
NOTES
The lockfile is created exactly as named on the command line. The ex-
tension ".lock" is not automatically appended.
This utility is a lot like the lockfile(1) utility included with proc-
mail, and the mutt_dotlock(1) utility included with mutt. However the
command-line arguments differ, and so does the return status. It is
believed, that dotlockfile is the most flexible implementation, since
it automatically detects when it needs to use privileges to lock a
mailbox, and does it safely.
The above mentioned lockfile_create(3) manpage is present in the li-
blockfile-dev package.
BUGS
None known.
SEE ALSO
lockfile_create(3), maillock(3)
AUTHOR
Miquel van Smoorenburg
January 10, 2017 DOTLOCKFILE(1)
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