path: root/man2/mknod.2

.\" Hey Emacs! This file is -*- nroff -*- source.
.\"
.\" This manpage is Copyright (C) 1992 Drew Eckhardt;
.\"                               1993 Michael Haardt
.\"                               1993,1994 Ian Jackson.
.\" You may distribute it under the terms of the GNU General
.\" Public License. It comes with NO WARRANTY.
.\"
.\" Modified 1996-08-18 by urs
.\" Modified 2003-04-23 by Michael Kerrisk
.\" Modified 2004-06-23 by Michael Kerrisk <mtk.manpages@gmail.com>
.\"
.TH MKNOD 2 2010-09-20 "Linux" "Linux Programmer's Manual"
.SH NAME
mknod \- create a special or ordinary file
.SH SYNOPSIS
.nf
.B #include <sys/types.h>
.B #include <sys/stat.h>
.B #include <fcntl.h>
.B #include <unistd.h>
.sp
.BI "int mknod(const char *" pathname ", mode_t " mode ", dev_t " dev );
.fi
.sp
.in -4n
Feature Test Macro Requirements for glibc (see
.BR feature_test_macros (7)):
.in
.sp
.BR mknod ():
.ad l
.RS 4
_BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE\ >=\ 500 ||
_XOPEN_SOURCE\ &&\ _XOPEN_SOURCE_EXTENDED
.RE
.ad
.SH DESCRIPTION
The system call
.BR mknod ()
creates a file system node (file, device special file or
named pipe) named
.IR pathname ,
with attributes specified by
.I mode
and
.IR dev .

The
.I mode
argument specifies both the permissions 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 the permissions for the new node.

The permissions are modified by the process's
.I umask
in the usual way: the permissions of the created node are
.IR "(mode & ~umask)" .

The file type must be one of
.BR S_IFREG ,
.BR S_IFCHR ,
.BR S_IFBLK ,
.B S_IFIFO
or
.B S_IFSOCK
.\" (S_IFSOCK since Linux 1.2.4)
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
.BR S_IFREG .)

If the file type is
.B S_IFCHR
or
.B S_IFBLK
then
.I dev
specifies the major and minor numbers of the newly created device
special file
.RB ( makedev (3)
may be useful to build the value for
.IR dev );
otherwise it is ignored.

If
.I pathname
already exists, or is a symbolic link, this call fails with an
.B 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 file system 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.
.SH "RETURN VALUE"
.BR mknod ()
returns zero on success, or \-1 if an error occurred (in which case,
.I errno
is set appropriately).
.SH ERRORS
.TP
.B EACCES
The parent directory does not allow write permission to the process,
or one of the directories in the path prefix of
.I pathname
did not allow search permission.
(See also
.BR path_resolution (7).)
.TP
.B EEXIST
.I pathname
already exists.
This includes the case where
.I pathname
is a symbolic link, dangling or not.
.TP
.B EFAULT
.IR pathname " points outside your accessible address space."
.TP
.B EINVAL
.I mode
requested creation of something other than a regular file, device
special file, FIFO or socket.
.TP
.B ELOOP
Too many symbolic links were encountered in resolving
.IR pathname .
.TP
.B ENAMETOOLONG
.IR pathname " was too long."
.TP
.B ENOENT
A directory component in
.I pathname
does not exist or is a dangling symbolic link.
.TP
.B ENOMEM
Insufficient kernel memory was available.
.TP
.B ENOSPC
The device containing
.I pathname
has no room for the new node.
.TP
.B ENOTDIR
A component used as a directory in
.I pathname
is not, in fact, a directory.
.TP
.B EPERM
.I 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
.B CAP_MKNOD
capability);
.\" For Unix domain sockets and regular files, EPERM is only returned in
.\" Linux 2.2 and earlier; in Linux 2.4 and later, unprivileged can
.\" use mknod() to make these files.
also returned if the file system containing
.I pathname
does not support the type of node requested.
.TP
.B EROFS
.I pathname
refers to a file on a read-only file system.
.SH "CONFORMING TO"
SVr4, 4.4BSD, POSIX.1-2001 (but see below).
.\" The Linux version differs from the SVr4 version in that it
.\" does not require root permission to create pipes, also in that no
.\" EMULTIHOP, ENOLINK, or EINTR error is documented.
.SH NOTES
POSIX.1-2001 says: "The only portable use of
.BR mknod ()
is to create a FIFO-special file.
If
.I mode
is not
.B S_IFIFO
or
.I dev
is not 0, the behavior of
.BR mknod ()
is unspecified."
However, nowadays one should never use
.BR mknod ()
for this purpose; one should use
.BR mkfifo (3),
a function especially defined for this purpose.

Under Linux, this call cannot be used to create directories.
One should make directories with
.BR mkdir (2).
.\" and one should make Unix domain sockets with socket(2) and bind(2).

There are many infelicities in the protocol underlying NFS.
Some of these affect
.BR mknod ().
.SH "SEE ALSO"
.BR chmod (2),
.BR chown (2),
.BR fcntl (2),
.BR mkdir (2),
.BR mknodat (2),
.BR mount (2),
.BR socket (2),
.BR stat (2),
.BR umask (2),
.BR unlink (2),
.BR makedev (3),
.BR mkfifo (3),
.BR path_resolution (7)