mknod()

Updated: October 26, 2022

Make a new filesystem entry

Synopsis:

#include <sys/types.h>
#include <unistd.h>
#include <sys/stat.h>

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

Arguments:

path
The pathname that you want to use for the file.
mode
A set of bits that define the file type and access permissions that you want to use. The valid file types are:
  • S_IFDIR — create a directory.
  • S_IFIFO — create a FIFO.

For more information, see the entry for struct stat.

dev
Ignored.

Library:

libc

Use the -l c option to qcc to link against this library. This library is usually included automatically.

Description:

The mknod() function makes a file, named path, using the file type encoded in the mode argument. Supported file types are directories and FIFOs.

Note: This function is included to enhance portability with software written for Unix-compatible operating systems. For POSIX portability, use mkdir() or mkfifo() instead.
To make a directory with read-write-execute permissions for everyone, you could use the following:
mknod (name, S_IFDIR | 0777, 0);

Returns:

0
Success.
-1
An error occurred (errno is set).

Errors:

EACCES
A component of the path prefix denies search permission, or write permission is denied for the parent directory.
EEXIST
The named file already exists.
ELOOP
There are too many levels of symbolic links or prefixes.
EMLINK
The link count of the parent directory would exceed LINK_MAX.
ENAMETOOLONG
The length of the path string exceeds PATH_MAX, or a pathname component is longer than NAME_MAX.
ENOENT
A component of the path prefix doesn't exist, or the path argument points to an empty string.
ENOSPC
The filesystem doesn't contain enough space to hold the contents of the new directory or to extend the parent directory, or the maximum limit of files and directories has been reached.
ENOSYS
The mknod() function isn't implemented for the filesystem underlying the specified path.
ENOTDIR
A component of the path prefix isn't a directory.
EROFS
The named file resides on a read-only filesystem.

Examples:

/*
 * Create special files as a directory or FIFO
 */
#include <stdio.h>
#include <stdlib.h>
#include <sys/stat.h>
#include <unistd.h>

int main( int argc, char** argv )
  {
    int c;
    mode_t mode = 0666;
    int ecode = 0;

    if( argc == 1 ) {
      printf( "Use: %s [-d directory] ... [-f fifo] ... \n",
          argv[0] );
      return( 0 );
    }

    while(( c = getopt( argc, argv, "d:f:" )) != -1 ) {
      switch( c ) {
        case 'd': mode = S_IFDIR | 0666; break;
        case 'f': mode = S_IFIFO | 0666; break;
      }

      if( mknod( optarg, mode, 0 ) != 0 ) {
        perror( optarg );
        ++ecode;
      }
    }

    return( ecode );
  }

Classification:

POSIX 1003.1

Safety:  
Cancellation point No
Interrupt handler No
Signal handler Yes
Thread Yes