MKNOD(2) System Calls MKNOD(2)

NAME

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

SYNOPSIS

#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);

DESCRIPTION

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:

S_IFIFO
fifo special


S_IFCHR
character special


S_IFDIR
directory


S_IFBLK
block special


S_IFREG
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
owner.
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.

RETURN VALUES

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.

ERRORS

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

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


EDQUOT
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.


EEXIST
The named file exists.


EFAULT
The path argument points to an illegal address.


EINTR
A signal was caught during the execution of the
mknod() function.


EINVAL
An invalid argument exists.


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


ELOOP
Too many symbolic links were encountered in
translating path.


ENAMETOOLONG
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.


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


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link to that machine is no longer active.


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


ENOTDIR
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.


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


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


The mknodat() function will fail if:

EBADF
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:

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

USAGE

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).

ATTRIBUTES

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


+--------------------+-------------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+--------------------+-------------------+
|Interface Stability | Standard |
+--------------------+-------------------+
|MT-Level | Async-Signal-Safe |
+--------------------+-------------------+

SEE ALSO

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),
standards(7)

February 19, 2004 MKNOD(2)