MKNOD(2) System Calls MKNOD(2)


mknod, mknodat - make a directory, a special file, or a regular file


#include <sys/stat.h>

int mknod(const char *path, mode_t mode, dev_t dev);

int mknodat(int fd, const char *path, mode_t mode, dev_t dev);


The mknod() and mknodat() function creates a new file named by the path
name pointed to by path. The file type and permissions of the new file
are initialized from mode.

The file type is specified in mode by the S_IFMT bits, which must be set
to one of the following values:

fifo special

character special


block special

ordinary file

The file access permissions are specified in mode by the 0007777 bits,
and may be constructed by a bitwise OR operation of the following values:

S_ISUID 04000 Set user ID on execution.
S_ISGID 020#0 Set group ID on execution if # is 7, 5,
3, or 1. Enable mandatory file/record
locking if # is 6, 4, 2, or 0
S_ISVTX 01000 On directories, restricted deletion
flag; on regular files on a UFS file
system, do not cache flag.
S_IRWXU 00700 Read, write, execute by owner.
S_IRUSR 00400 Read by owner.
S_IWUSR 00200 Write by owner.
S_IXUSR 00100 Execute (search if a directory) by
S_IRWXG 00070 Read, write, execute by group.
S_IRGRP 00040 Read by group.
S_IWGRP 00020 Write by group.
S_IXGRP 00010 Execute by group.
S_IRWXO 00007 Read, write, execute (search) by others.
S_IROTH 00004 Read by others.
S_IWOTH 00002 Write by others
S_IXOTH 00001 Execute by others.

The owner ID of the file is set to the effective user ID of the process.
The group ID of the file is set to the effective group ID of the process.
However, if the S_ISGID bit is set in the parent directory, then the
group ID of the file is inherited from the parent. If the group ID of
the new file does not match the effective group ID or one of the
supplementary group IDs, the S_ISGID bit is cleared.

The access permission bits of mode are modified by the process's file
mode creation mask: all bits set in the process's file mode creation mask
are cleared (see umask(2)). If mode indicates a block or character
special file, dev is a configuration-dependent specification of a
character or block I/O device. If mode does not indicate a block special
or character special device, dev is ignored. See makedev(3C).

If path is a symbolic link, it is not followed.

The mknodat() function is similar to mknod(); however, when path is a
relative path, it is resolved starting at the directory represented by
the file descriptor fd. To start at the current working directory, fd may
be set to the special value AT_FDCWD.


Upon successful completion, mknod() and mknodat() return 0. Otherwise,
they return -1, the new file is not created, and errno is set to indicate
the error.


The mknod() and mknodat() functions will fail if:

A component of the path prefix denies search permission,
or write permission is denied on the parent directory.

The directory where the new file entry is being placed
cannot be extended because the user's quota of disk
blocks on that file system has been exhausted, or the
user's quota of inodes on the file system where the file
is being created has been exhausted.

The named file exists.

The path argument points to an illegal address.

A signal was caught during the execution of the mknod()

An invalid argument exists.

An I/O error occurred while accessing the file system.

Too many symbolic links were encountered in translating

The length of the path argument exceeds {PATH_MAX}, or
the length of a path component exceeds {NAME_MAX} while
_POSIX_NO_TRUNC is in effect.

A component of the path prefix specified by path does not
name an existing directory or path is an empty string.

The path argument points to a remote machine and the link
to that machine is no longer active.

The directory that would contain the new file cannot be
extended or the file system is out of file allocation

A component of the path prefix is not a directory. In
addition, when calling mknodat(), if path is a relative
path and fd is a valid file descriptor which does not
refer to a directory.

Not all privileges are asserted in the effective set of
the calling process.

The directory in which the file is to be created is
located on a read-only file system.

The mknodat() function will fail if:

The path argument is a relative path and fd is not a
valid open file descriptor or the special value AT_FDCWD.

The mknod() function may fail if:

Pathname resolution of a symbolic link produced an
intermediate result whose length exceeds {PATH_MAX}.


Applications should use the mkdir(2) function to create a directory
because appropriate permissions are not required and because mknod()
might not establish directory entries for the directory itself (.) and
the parent directory (..). The mknod() function can be invoked only by a
privileged user for file types other than FIFO special. The mkfifo(3C)
function should be used to create FIFOs.

Doors are created using door_create(3C) and can be attached to the file
system using fattach(3C). Symbolic links can be created using symlink(2).
An endpoint for communication can be created using socket(3SOCKET).


See attributes(7) for descriptions of the following attributes:

|Interface Stability | Standard |
|MT-Level | Async-Signal-Safe |


chmod(2), creat(2), exec(2), mkdir(2), open(2), stat(2), symlink(2),
umask(2), door_create(3C), fattach(3C), makedev(3C), mkfifo(3C),
stat.h(3HEAD), socket(3SOCKET), attributes(7), privileges(7),

February 19, 2004 MKNOD(2)