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MKNOD(3P)		   POSIX Programmer's Manual		     MKNOD(3P)

PROLOG
       This  manual  page is part of the POSIX Programmer's Manual.  The Linux
       implementation of this interface may differ (consult the	 corresponding
       Linux  manual page for details of Linux behavior), or the interface may
       not be implemented on Linux.

NAME
       mknod, mknodat — make directory, special file, or 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() function shall create a new file named by the  pathname  to
       which the argument path points.

       The  file type for path is OR'ed into the mode argument, and the appli‐
       cation shall select one of the following symbolic constants:

		   ┌───────────┬──────────────────────────────────┐
		   │   Name    │	   Description		  │
		   ├───────────┼──────────────────────────────────┤
		   │S_IFIFO    │ FIFO-special			  │
		   │S_IFCHR    │ Character-special (non-portable) │
		   │S_IFDIR    │ Directory (non-portable)	  │
		   │S_IFBLK    │ Block-special (non-portable)	  │
		   │S_IFREG    │ Regular (non-portable)		  │
		   └───────────┴──────────────────────────────────┘
       The only portable use of mknod() is to create a FIFO-special  file.  If
       mode is not S_IFIFO or dev is not 0, the behavior of mknod() is unspec‐
       ified.

       The permissions for the new file are OR'ed into the mode argument,  and
       may  be	selected  from	any combination of the following symbolic con‐
       stants:

	     ┌───────────┬─────────────────────────────────────────────┐
	     │	 Name	 │		   Description		       │
	     ├───────────┼─────────────────────────────────────────────┤
	     │S_ISUID	 │ Set user ID on execution.		       │
	     │S_ISGID	 │ Set group ID on execution.		       │
	     │S_IRWXU	 │ Read, write, or execute (search) by owner.  │
	     │S_IRUSR	 │ Read by owner.			       │
	     │S_IWUSR	 │ Write by owner.			       │
	     │S_IXUSR	 │ Execute (search) by owner.		       │
	     │S_IRWXG	 │ Read, write, or execute (search) by group.  │
	     │S_IRGRP	 │ Read by group.			       │
	     │S_IWGRP	 │ Write by group.			       │
	     │S_IXGRP	 │ Execute (search) by group.		       │
	     │S_IRWXO	 │ Read, write, or execute (search) by others. │
	     │S_IROTH	 │ Read by others.			       │
	     │S_IWOTH	 │ Write by others.			       │
	     │S_IXOTH	 │ Execute (search) by others.		       │
	     │S_ISVTX	 │ On directories, restricted deletion flag.   │
	     └───────────┴─────────────────────────────────────────────┘
       The user ID of the file shall be initialized to the effective  user  ID
       of the process. The group ID of the file shall be initialized to either
       the effective group ID of the process or the group  ID  of  the	parent
       directory. Implementations shall provide a way to initialize the file's
       group ID to the group ID of the parent directory. Implementations  may,
       but  need  not, provide an implementation-defined way to initialize the
       file's group ID to the effective group ID of the calling	 process.  The
       owner,  group,  and  other permission bits of mode shall be modified by
       the file mode creation mask of the process. The mknod() function	 shall
       clear  each  bit whose corresponding bit in the file mode creation mask
       of the process is set.

       If path names a symbolic link, mknod() shall  fail  and	set  errno  to
       [EEXIST].

       Upon successful completion, mknod() shall mark for update the last data
       access, last data modification, and last file status change  timestamps
       of  the	file.  Also,  the  last data modification and last file status
       change timestamps of the directory that contains the new entry shall be
       marked for update.

       Only  a process with appropriate privileges may invoke mknod() for file
       types other than FIFO-special.

       The mknodat() function shall be	equivalent  to	the  mknod()  function
       except  in  the case where path specifies a relative path. In this case
       the newly created directory, special file, or regular file  is  located
       relative	 to  the  directory  associated	 with  the  file descriptor fd
       instead of the current working directory. If the	 file  descriptor  was
       opened  without	O_SEARCH,  the	function shall check whether directory
       searches are permitted using the current permissions of	the  directory
       underlying  the file descriptor. If the file descriptor was opened with
       O_SEARCH, the function shall not perform the check.

       If mknodat() is passed the special value AT_FDCWD in the fd  parameter,
       the  current  working directory shall be used and the behavior shall be
       identical to a call to mknod().

RETURN VALUE
       Upon successful completion, these functions shall return 0.  Otherwise,
       these functions shall return −1 and set errno to indicate the error. If
       −1 is returned, the new file shall not be created.

ERRORS
       These functions shall fail if:

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

       EEXIST The named file exists.

       EINVAL An invalid argument exists.

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

       ELOOP  A loop exists in symbolic links encountered during resolution of
	      the path argument.

       ENAMETOOLONG
	      The  length  of  a  component  of	 a  pathname  is  longer  than
	      {NAME_MAX}.

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

       ENOENT or ENOTDIR
	      The path argument contains at least  one	non-<slash>  character
	      and  ends	 with one or more trailing <slash> characters. If path
	      names an existing file, an [ENOENT] error shall not occur.

       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 names an existing file that is
	      neither a directory nor a symbolic link to a directory.

       EPERM  The invoking process does not have  appropriate  privileges  and
	      the file type is not FIFO-special.

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

       The mknodat() function shall fail if:

       EACCES fd was not opened with  O_SEARCH	and  the  permissions  of  the
	      directory underlying fd do not permit directory searches.

       EBADF  The  path	 argument does not specify an absolute path and the fd
	      argument is neither AT_FDCWD nor a valid	file  descriptor  open
	      for reading or searching.

       ENOTDIR
	      The  path	 argument  is  not  an	absolute path and fd is a file
	      descriptor associated with a non-directory file.

       These functions may fail if:

       ELOOP  More than {SYMLOOP_MAX} symbolic links were  encountered	during
	      resolution of the path argument.

       ENAMETOOLONG
	      The length of a pathname exceeds {PATH_MAX}, or pathname resolu‐
	      tion of a symbolic link produced an intermediate result  with  a
	      length that exceeds {PATH_MAX}.

       The following sections are informative.

EXAMPLES
   Creating a FIFO Special File
       The  following  example	shows  how to create a FIFO special file named
       /home/cnd/mod_done, with read/write permissions	for  owner,  and  with
       read permissions for group and others.

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

	   dev_t dev;
	   int	 status;
	   ...
	   status  = mknod("/home/cnd/mod_done", S_IFIFO | S_IWUSR |
	       S_IRUSR | S_IRGRP | S_IROTH, dev);

APPLICATION USAGE
       The  mkfifo()  function is preferred over this function for making FIFO
       special files.

RATIONALE
       The POSIX.1‐1990 standard required that the group ID of a newly created
       file be set to the group ID of its parent directory or to the effective
       group ID of the creating process. FIPS 151‐2 required that  implementa‐
       tions  provide a way to have the group ID be set to the group ID of the
       containing directory, but did not prohibit  implementations  also  sup‐
       porting a way to set the group ID to the effective group ID of the cre‐
       ating process.  Conforming applications should not assume  which	 group
       ID  will	 be used. If it matters, an application can use chown() to set
       the group ID after the file is created, or determine under what	condi‐
       tions the implementation will set the desired group ID.

       The purpose of the mknodat() function is to create directories, special
       files, or regular files in directories other than the  current  working
       directory  without exposure to race conditions. Any part of the path of
       a file could be changed in parallel to a call to mknod(), resulting  in
       unspecified  behavior.  By  opening  a  file  descriptor for the target
       directory and using the mknodat() function it can  be  guaranteed  that
       the  newly  created directory, special file, or regular file is located
       relative to the desired directory.

FUTURE DIRECTIONS
       None.

SEE ALSO
       chmod(), creat(), exec, fstatat(), mkdir(), mkfifo(), open(), umask()

       The Base Definitions volume of POSIX.1‐2008, <sys_stat.h>

COPYRIGHT
       Portions of this text are reprinted and reproduced in  electronic  form
       from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
       -- Portable Operating System Interface (POSIX),	The  Open  Group  Base
       Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri‐
       cal and Electronics Engineers,  Inc  and	 The  Open  Group.   (This  is
       POSIX.1-2008  with  the	2013  Technical Corrigendum 1 applied.) In the
       event of any discrepancy between this version and the original IEEE and
       The  Open Group Standard, the original IEEE and The Open Group Standard
       is the referee document. The original Standard can be  obtained	online
       at http://www.unix.org/online.html .

       Any  typographical  or  formatting  errors that appear in this page are
       most likely to have been introduced during the conversion of the source
       files  to  man page format. To report such errors, see https://www.ker‐
       nel.org/doc/man-pages/reporting_bugs.html .

IEEE/The Open Group		     2013			     MKNOD(3P)
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