mknod() — Make a directory or file

Standards

Standards / Extensions	C or C++	Dependencies
XPG4.2 Single UNIX Specification, Version 3 z/OS® UNIX	both

Format

_OPEN_SYS

#define _OPEN_SYS
#include <sys/stat.h>

int mknod(const char *path, mode_t mode, rdev_t dev_identifier);

_XOPEN_SOURCE_EXTENDED 1

#define _XOPEN_SOURCE_EXTENDED 1
#include <sys/stat.h>

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

General description

Creates a new directory, regular file, character special file, or FIFO special file (named pipe), with the pathname specified in the path argument.

The first byte of the mode argument determines the file type of the file:

S_IFCHR: Character special file
S_IFFIFO: FIFO special file
S_IFREG: Regular file
S_IFDIR: Directory file

The file permission bits of the new file are initialized with the remaining bits in mode and changed by the file creation mask of the process. For more information on these symbols, refer to chmod() — Change the mode of a file or directory.

dev_identifier applies only to a character special file. It is ignored for the other file types. dev_identifier contains a value representing the device major and device minor numbers. The major number is contained in the high-order 16 bits; it identifies a device driver supporting a class of devices, such as interactive terminals. The minor number is contained in the low-order 16 bits of dev_identifier; it identifies a specific device within the class referred to by the device major number. With z/OS UNIX services, the device major numbers are:

1: Master pseudoterminal
2: Slave pseudoterminal
3: /dev/tty
4: /dev/null
5: /dev/fdn
6: Sockets
7: OCSRTY
8: OCSADMIN
9: "/dev/console"

Device major numbers 1,2 and 7: The device minor numbers range between 0 and one less than the maximum number of pseudoterminal pairs defined by the installation.

Device major numbers 3,4,6,8 and 9: The device minor number is ignored.

Device major number 5: The device minor number value represents the file descriptor to be referred to. For example, device minor 0 refers to file descriptor 0.

When it completes successfully, mknod() marks for update the following fields of the file: st_atime, st_ctime, and st_mtime. It also marks for update the st_ctime and st_mtime fields of the directory that contains the new file.

Returned value

If successful, mknod() returns 0.

If unsuccessful, mknod() returns -1 and sets errno to one of the following values:

Error Code: Description
EACCES: Search permission is denied on a component of path, or write permission is denied on the parent directory of the file to be created.
EEXIST: A file by that name already exists.
ELOOP: A loop exists in symbolic links. This error is issued if more than POSIX_SYMLOOP (defined in the limits.h header file) symbolic links are detected in the resolution of path.
EMLINK: The link count of the parent directory has already reached the maximum defined for the system.
ENAMETOOLONG: pathname is longer than PATH_MAX characters, or some component of pathname is longer than NAME_MAX characters while _POSIX_NO_TRUNC is in effect. For symbolic links, the length of the pathname string substituted for a symbolic link exceeds PATH_MAX. The PATH_MAX and NAME_MAX values can be determined through pathconf().
ENOENT: A component of path was not found, or no path was specified.
ENOSPC: The file system does not have enough space to contain a new directory, or the parent directory cannot be extended.
ENOTDIR: A component of path is not a directory
EPERM: Added for XPG4.2: The invoking process does not have appropriate privileges and the file type is not FIFO-special.
EROFS: The file named in path cannot be created, because it would reside on a read-only file system.

Example

CELEBM18

/* CELEBM18 */                                   
#include <sys/stat.h>                                                           
#include <unistd.h>                                                             
#include <stdio.h>                                                              
                                                                                
#define master 0x00010000                                                       
                                                                                
main() {                                                                        
  char fn[]="char   ec";                                                        
                                                                                
  if (mknod(fn, S_IFCHR|S_IRUSR|S_IWUSR, master|0x0001) != 0)                   
    perror("mknod() error");                                                    
  else if (unlink(fn) != 0)                                                     
    perror("unlink() error");                                                   
}