mknod, mknodat, mkfifo or mkfifoat, Subroutine

Purpose

Creates an ordinary file, first-in-first-out (FIFO), or special file.

Library

Standard C Library (libc.a)

Syntax

#include <sys/stat.h>

int mknodat (int DirFileDescriptor, const char * Path, mode_tMode, dev_tDevice)
int DirFileDescriptor;
char *Path;
int Mode;
dev_t Device;

int mkfifo (const char *Path, mode_t Mode)
const char *Path;
int Mode;

int mkfifoat (int DirFileDescriptor, const char *Path, mode_tMode)
int DirFileDescriptor;
const char *Path;
int Mode;

Description

The mknod and mknodat subroutines create a new regular file, special file, or FIFO file. Using the mknod or mknodat subroutine to create file types (other than FIFO or special files) requires root user authority.

For the mknod or mknodat subroutine to complete successfully, a process must have both search and write permission in the parent directory of the Path parameter.

The mkfifo and mkfifoat subroutines are interfaces to the mknod subroutine, where the new file to be created is a FIFO or special file. No special system privileges are required.

The new file has the following characteristics:

• File type is specified by the Mode parameter.
• Owner ID is set to the effective user ID of the process.
• Group ID of the file is set to the group ID of the parent directory if the SetGroupID attribute (S_ISGID) of the parent directory is set. Otherwise, the group ID of the file is set to the effective group ID of the calling process.
• Permission and attribute bits are set according to the value of the Mode parameter. All bits set in the file-mode creation mask of the process are cleared.

Upon successful completion, the mkfifo subroutine marks for update the st_atime, st_ctime, and st_mtime fields of the file. It also marks for update the st_ctime and st_mtime fields of the directory that contains the new entry.

If the new file is a character special file having the S_IMPX attribute (multiplexed character special file), when the file is used, additional path-name components can appear after the path name as if it were a directory. The additional part of the path name is available to the device driver of the file for interpretation. This feature provides a multiplexed interface to the device driver.

The mknodat subroutine is equivalent to the mknod subroutine, and the mkfifoat subroutine is equivalent to the mkfifo subroutine if the DirFileDescriptor parameter is AT_FDCWD or Path is an absolute path name. If DirFileDescriptor is a valid file descriptor of an open directory and Path is a relative path name, Path is considered to be relative to the directory that is associated with the DirFileDescriptor parameter instead of the current working directory.

If DirFileDescriptor was opened without the O_SEARCH open flag, the subroutine checks to determine whether directory searches are permitted for that directory by using the current permissions of the directory. If the directory was opened with the O_SEARCH open flag, the subroutine does not perform the check for that directory.

Parameters

Return Values

Upon successful completion, a value of 0 is returned. Otherwise, a value of -1 is returned and the errno global variable is set to indicate the error.

Error Codes

The mknod and mknodat subroutines fail and the new file is not created if one or more of the following are true:

The mknodat and mkfifoat subroutines fail and the new file is not created if one or more of the following are true:

The mknod, mknodat, mkfifo, and mkfifoat subroutines can be unsuccessful for other reasons. See "Appendix. A Base Operating System Error Codes for Services That Require Path-Name Resolution" for a list of additional errors.

If NFS is installed on the system, the subroutines can also fail if the following is true: