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 $NetBSD: mknod.2,v 1.31 2019/06/20 06:59:32 wiz Exp $

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 @(#)mknod.2 8.1 (Berkeley) 6/4/93

.Dd June 20, 2019
.Dt MKNOD 2
.Os
.Sh NAME
.Nm mknod ,
.Nm mknodat
.Nd make a special file node
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
n sys/stat.h .Ft int
.Fn mknod "const char *path" "mode_t mode" "dev_t dev"
n sys/stat.h n fcntl.h .Ft int
.Fn mknodat "int fd" "const char *path" "mode_t mode" "dev_t dev"
.Sh DESCRIPTION
.Nm
with
.Dv S_IFIFO
specified in
.Fa mode
and 0 in
.Fa dev
makes a FIFO file.
This call is respectively a portable alias for
.Xr mkfifo 2
and
.Xr mkfifoat 2 .

p
.Nm
with
.Dv S_IFCHR
or
.Dv S_IFBLK
in
.Fa mode
makes a device special file.
The file
.Fa path
is created with the major and minor
device numbers specified by
.Fa dev .
The access permissions of
.Fa path
are extracted from
.Fa mode ,
modified by the
.Xr umask 2
of the parent process.

p
.Fn mknodat
works the same way as
.Fn mknod
except if
.Fa path
is relative.
In that case, it is looked up from a directory whose file
descriptor was passed as
.Fa fd .
Search permission is required on this directory.
 (These alternatives await a decision about the semantics of O_SEARCH)
 Search permission is required on this directory
 except if
 .Fa fd
 was opened with the
 .Dv O_SEARCH
 flag.
 - or -
 This file descriptor must have been opened with the
 .Dv O_SEARCH
 flag.
.Fa fd
can be set to
.Dv AT_FDCWD
in order to specify the current directory.

p
.Fn mknod
requires super-user privileges for creating device special files.
.Sh RETURN VALUES
.Rv -std mknod mknodat
.Sh ERRORS
.Fn mknod
and
.Fn mknodat
will fail and the file will be not created if:
l -tag -width Er t Bq Er EACCES Search permission is denied for a component of the path prefix.
t Bq Er EDQUOT The directory in which the entry for the new node
is being placed cannot be extended because the
user's quota of disk blocks on the file system
containing the directory has been exhausted; or
the user's quota of inodes on the file system on
which the node is being created has been exhausted.
t Bq Er EEXIST The named file exists.
t Bq Er EFAULT .Fa path
points outside the process's allocated address space.
t Bq Er EINVAL The supplied
.Fa mode
or
.Fa dev
is invalid.
t Bq Er EIO An I/O error occurred while making the directory entry or allocating the inode.
t Bq Er ELOOP Too many symbolic links were encountered in translating the pathname.
t Bq Er ENAMETOOLONG A component of a pathname exceeded
rq Dv NAME_MAX characters, or an entire path name exceeded
rq Dv PATH_MAX characters.
t Bq Er ENOENT A component of the path prefix does not exist.
t Bq Er ENOSPC The directory in which the entry for the new node is being placed
cannot be extended because there is no space left on the file
system containing the directory; or
there are no free inodes on the file system on which the
node is being created.
t Bq Er ENOTDIR A component of the path prefix is not a directory.
t Bq Er EOPNOTSUPP The kernel has not been configured to support FIFOs.
t Bq Er EPERM The process's effective user ID is not super-user.
t Bq Er EROFS The named file resides on a read-only file system.
.El

p
In addition,
.Fn mknodat
will fail if:
l -tag -width Er t Bq Er EBADF .Fa path
does not specify an absolute path and
.Fa fd
is neither
.Dv AT_FDCWD
nor a valid file descriptor open for reading or searching.
t Bq Er ENOTDIR .Fa path
is not an absolute path and
.Fa fd
is a file descriptor associated with a non-directory file.
.El
.Sh SEE ALSO
.Xr chmod 2 ,
.Xr mkfifo 2 ,
.Xr stat 2 ,
.Xr umask 2 ,
.Xr makedev 3
.Sh STANDARDS
The
.Fn mknod
function conforms to
.St -p1003.1-90 .
.Fn mknodat
conforms to
.St -p1003.1-2008 .
.Sh HISTORY
A
.Fn mknod
function call appeared in
.At v6 .

p
The alias mode for
.Xr mkfifo 2
and
.Xr mkfifoat 2
first appeared in
.Nx 9 .