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MKNOD(2) Linux Programmer's Manual MKNOD(2)
NAME
mknod, mknodat - create a special or ordinary file
SYNOPSIS
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.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():
_BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 500 ||
_XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED
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 permissions to use and the type of node to be cre‐
ated. It should be a combination (using bitwise OR) of one of the file types listed below
and the permissions for the new node.
The permissions are modified by the process's umask in the usual way: 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), character special file, block special file,
FIFO (named pipe), or UNIX domain 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; otherwise 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(2), 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(2) for a relative pathname).
If pathname is relative and dirfd is the special value AT_FDCWD, then pathname is inter‐
preted relative to the current working directory of the calling process (like mknod(2)).
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, or -1 if an error occurred (in which case,
errno is set appropriately).
ERRORS
EACCES The parent directory does not allow write permission to the process, or one of the
directories in the path prefix of pathname did not allow search permission. (See
also path_resolution(7).)
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 dangling 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.
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.
The following additional errors can occur for mknodat():
EBADF dirfd is not a valid file descriptor.
ENOTDIR
pathname is relative and dirfd is a file descriptor referring to a file other than
a directory.
VERSIONS
mknodat() was added to Linux in kernel 2.6.16; library support was added to glibc in ver‐
sion 2.4.
CONFORMING TO
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 behavior of mknod() is unspecified." However,
nowadays one should never use mknod() for this purpose; one should use mkfifo(3), a func‐
tion especially 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(2).
SEE ALSO
chmod(2), chown(2), fcntl(2), mkdir(2), mount(2), socket(2), stat(2), umask(2), unlink(2),
makedev(3), mkfifo(3), path_resolution(7)
COLOPHON
This page is part of release 3.74 of the Linux man-pages project. A description of the
project, information about reporting bugs, and the latest version of this page, can be
found at http://www.kernel.org/doc/man-pages/.
Linux 2014-02-21 MKNOD(2)
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