mknod(2) System Calls Manual mknod(2)
NAME
mknod, mknodat - create a special or ordinary file
LIBRARY
Standard C library (libc, -lc)
SYNOPSIS
#include <sys/stat.h>
int mknod(const char *pathname, mode_t mode, dev_t dev);
#include <fcntl.h> /* Definition of AT_* constants */
#include <sys/stat.h>
int mknodat(int dirfd, const char *pathname, mode_t mode, dev_t dev);
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
mknod():
_XOPEN_SOURCE >= 500
|| /* Since glibc 2.19: */ _DEFAULT_SOURCE
|| /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
DESCRIPTION
The system call mknod() creates a filesystem node (file, device special
file, or named pipe) named pathname, with attributes specified by mode
and dev.
The mode argument specifies both the file mode to use and the type of
node to be created. It should be a combination (using bitwise OR) of
one of the file types listed below and zero or more of the file mode
bits listed in inode(7).
The file mode is modified by the process's umask in the usual way: in
the absence of a default ACL, the permissions of the created node are
(mode & ~umask).
The file type must be one of S_IFREG, S_IFCHR, S_IFBLK, S_IFIFO, or
S_IFSOCK to specify a regular file (which will be created empty), char-
acter special file, block special file, FIFO (named pipe), or UNIX do-
main socket, respectively. (Zero file type is equivalent to type
S_IFREG.)
If the file type is S_IFCHR or S_IFBLK, then dev specifies the major
and minor numbers of the newly created device special file (makedev(3)
may be useful to build the value for dev); otherwise it is ignored.
If pathname already exists, or is a symbolic link, this call fails with
an EEXIST error.
The newly created node will be owned by the effective user ID of the
process. If the directory containing the node has the set-group-ID bit
set, or if the filesystem is mounted with BSD group semantics, the new
node will inherit the group ownership from its parent directory; other-
wise it will be owned by the effective group ID of the process.
mknodat()
The mknodat() system call operates in exactly the same way as mknod(),
except for the differences described here.
If the pathname given in pathname is relative, then it is interpreted
relative to the directory referred to by the file descriptor dirfd
(rather than relative to the current working directory of the calling
process, as is done by mknod() for a relative pathname).
If pathname is relative and dirfd is the special value AT_FDCWD, then
pathname is interpreted relative to the current working directory of
the calling process (like mknod()).
If pathname is absolute, then dirfd is ignored.
See openat(2) for an explanation of the need for mknodat().
RETURN VALUE
mknod() and mknodat() return zero on success. On error, -1 is returned
and errno is set to indicate the error.
ERRORS
EACCES The parent directory does not allow write permission to the
process, or one of the directories in the path prefix of path-
name did not allow search permission. (See also path_resolu-
tion(7).)
EBADF (mknodat()) pathname is relative but dirfd is neither AT_FDCWD
nor a valid file descriptor.
EDQUOT The user's quota of disk blocks or inodes on the filesystem has
been exhausted.
EEXIST pathname already exists. This includes the case where pathname
is a symbolic link, dangling or not.
EFAULT pathname points outside your accessible address space.
EINVAL mode requested creation of something other than a regular file,
device special file, FIFO or socket.
ELOOP Too many symbolic links were encountered in resolving pathname.
ENAMETOOLONG
pathname was too long.
ENOENT A directory component in pathname does not exist or is a dan-
gling symbolic link.
ENOMEM Insufficient kernel memory was available.
ENOSPC The device containing pathname has no room for the new node.
ENOTDIR
A component used as a directory in pathname is not, in fact, a
directory.
ENOTDIR
(mknodat()) pathname is relative and dirfd is a file descriptor
referring to a file other than a directory.
EPERM mode requested creation of something other than a regular file,
FIFO (named pipe), or UNIX domain socket, and the caller is not
privileged (Linux: does not have the CAP_MKNOD capability); also
returned if the filesystem containing pathname does not support
the type of node requested.
EROFS pathname refers to a file on a read-only filesystem.
VERSIONS
mknodat() was added in Linux 2.6.16; library support was added in glibc
2.4.
STANDARDS
mknod(): SVr4, 4.4BSD, POSIX.1-2001 (but see below), POSIX.1-2008.
mknodat(): POSIX.1-2008.
NOTES
POSIX.1-2001 says: "The only portable use of mknod() is to create a
FIFO-special file. If mode is not S_IFIFO or dev is not 0, the behav-
ior of mknod() is unspecified." However, nowadays one should never use
mknod() for this purpose; one should use mkfifo(3), a function espe-
cially defined for this purpose.
Under Linux, mknod() cannot be used to create directories. One should
make directories with mkdir(2).
There are many infelicities in the protocol underlying NFS. Some of
these affect mknod() and mknodat().
SEE ALSO
mknod(1), chmod(2), chown(2), fcntl(2), mkdir(2), mount(2), socket(2),
stat(2), umask(2), unlink(2), makedev(3), mkfifo(3), acl(5), path_reso-
lution(7)
Linux man-pages 6.03 2023-02-05 mknod(2)
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