mknod(S)

mknod -- make a directory, or a special or ordinary file

Synopsis

   #include <sys/types.h>
   #include <sys/stat.h>
   
   int mknod(const char path, mode_t mode, dev_t dev);

Description

mknod 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

For all file types other than S_IFIFO, the calling process must have the P_FILESYS privilege.

The file access permissions are specified in mode by the 0007777 bits, and may be constructed by an OR 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 Save text image after execution.

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(S)). 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(S).

mknod checks to see if the driver has been installed and whether or not it is an old-style driver. If the driver is installed and it is an old-style driver, the minor number is limited to 255. If it's not an old-style driver, then it must be a new-style driver or uninstalled, and the minor number is limited to the current value of the MAXMINOR tunable. Of course, this tunable is set to 255 by default. If the range check fails, mknod fails with EINVAL.

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

Return values

If mknod succeeds, it returns 0. If mknod fails, it returns -1 and sets errno to identify the error.

mknod fails and creates no new file if one or more of the following are true:

EEXIST: The named file exists.
EINVAL: dev is invalid.
EFAULT: path points outside the allocated address space of the process.
ELOOP: Too many symbolic links were encountered in translating path.
EMULTIHOP: Components of path require hopping to multiple remote machines and the file system type does not allow it.
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.
ENOTDIR: A component of the path prefix is not a directory.
ENOENT: A component of the path prefix does not exist or is a null pathname.
EPERM: The calling process does not have the P_FILESYS privilege.
EROFS: The directory in which the file is to be created is located on a read-only file system.
ENOSPC: No space is available.
EINTR: A signal was caught during the mknod system call.
ENOLINK: path points to a remote machine and the link to that machine is no longer active.

References

chmod(S), exec(S), makedev(S), mkdir(C), mkfifo(S), stat(M), umask(S)

S_IFIFO	fifo special
S_IFCHR	character special
S_IFDIR	directory
S_IFBLK	block special
S_IFREG	ordinary file

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	Save text image after execution.
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.