man-pages/man2/mknod.2

.\" This manpage is Copyright (C) 1992 Drew Eckhardt;
.\"             and Copyright (C) 1993 Michael Haardt
.\"             and Copyright (C) 1993,1994 Ian Jackson
.\"		and Copyright (C) 2006, 2014, Michael Kerrisk
.\"
.\" %%%LICENSE_START(GPL_NOVERSION_ONELINE)
.\" You may distribute it under the terms of the GNU General
.\" Public License. It comes with NO WARRANTY.
.\" %%%LICENSE_END
.\"
.\" 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 2021-08-27 "Linux" "Linux Programmer's Manual"
.SH NAME
mknod, mknodat \- create a special or ordinary file
.SH SYNOPSIS
.nf
.B #include <sys/stat.h>
.PP
.BI "int mknod(const char *" pathname ", mode_t " mode ", dev_t " dev );
.PP
.BR "#include <fcntl.h>           " "/* Definition of AT_* constants */"
.B #include <sys/stat.h>
.PP
.BI "int mknodat(int " dirfd ", const char *" pathname ", mode_t " mode \
", dev_t " dev );
.fi
.PP
.RS -4
Feature Test Macro Requirements for glibc (see
.BR feature_test_macros (7)):
.RE
.PP
.BR mknod ():
.nf
    _XOPEN_SOURCE >= 500
.\"    || _XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED
        || /* Since glibc 2.19: */ _DEFAULT_SOURCE
        || /* Glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
.fi
.SH DESCRIPTION
The system call
.BR mknod ()
creates a filesystem node (file, device special file, or
named pipe) named
.IR pathname ,
with attributes specified by
.I mode
and
.IR dev .
.PP
The
.I 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
.BR inode (7).
.PP
The file mode is modified by the process's
.I umask
in the usual way: in the absence of a default ACL, the permissions of the
created node are
.RI ( mode " & \(ti" umask ).
.PP
The file type must be one of
.BR S_IFREG ,
.BR S_IFCHR ,
.BR S_IFBLK ,
.BR 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 .)
.PP
If the file type is
.B S_IFCHR
or
.BR 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.
.PP
If
.I pathname
already exists, or is a symbolic link, this call fails with an
.B EEXIST
error.
.PP
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.
.\"
.\"
.SS mknodat()
The
.BR mknodat ()
system call operates in exactly the same way as
.BR mknod (),
except for the differences described here.
.PP
If the pathname given in
.I pathname
is relative, then it is interpreted relative to the directory
referred to by the file descriptor
.I dirfd
(rather than relative to the current working directory of
the calling process, as is done by
.BR mknod ()
for a relative pathname).
.PP
If
.I pathname
is relative and
.I dirfd
is the special value
.BR AT_FDCWD ,
then
.I pathname
is interpreted relative to the current working
directory of the calling process (like
.BR mknod ()).
.PP
If
.I pathname
is absolute, then
.I dirfd
is ignored.
.PP
See
.BR openat (2)
for an explanation of the need for
.BR mknodat ().
.SH RETURN VALUE
.BR mknod ()
and
.BR mknodat ()
return zero on success.
On error, \-1 is returned and
.I errno
is set to indicate the error.
.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 EBADF
.BR ( mknodat ())
.I pathname
is relative but
.I dirfd
is neither
.B AT_FDCWD
nor a valid file descriptor.
.TP
.B EDQUOT
The user's quota of disk blocks or inodes on the filesystem has been
exhausted.
.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 ENOTDIR
.BR ( mknodat ())
.I pathname
is relative and
.I dirfd
is a file descriptor referring to a file other than 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 returned only in
.\" Linux 2.2 and earlier; in Linux 2.4 and later, unprivileged can
.\" use mknod() to make these files.
also returned if the filesystem containing
.I pathname
does not support the type of node requested.
.TP
.B EROFS
.I pathname
refers to a file on a read-only filesystem.
.SH VERSIONS
.BR mknodat ()
was added to Linux in kernel 2.6.16;
library support was added to glibc in version 2.4.
.SH CONFORMING TO
.BR mknod ():
SVr4, 4.4BSD, POSIX.1-2001 (but see below), POSIX.1-2008.
.\" 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.
.PP
.BR mknodat ():
POSIX.1-2008.
.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.
.PP
Under Linux,
.BR mknod ()
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).
.PP
There are many infelicities in the protocol underlying NFS.
Some of these affect
.BR mknod ()
and
.BR mknodat ().
.SH SEE ALSO
.BR mknod (1),
.BR chmod (2),
.BR chown (2),
.BR fcntl (2),
.BR mkdir (2),
.BR mount (2),
.BR socket (2),
.BR stat (2),
.BR umask (2),
.BR unlink (2),
.BR makedev (3),
.BR mkfifo (3),
.BR acl (5),
.BR path_resolution (7)