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MKFIFO(3P)		   POSIX Programmer's Manual		    MKFIFO(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
       mkfifo, mkfifoat — make a FIFO special file relative to directory  file
       descriptor

SYNOPSIS
       #include <sys/stat.h>

       int mkfifo(const char *path, mode_t mode);
       int mkfifoat(int fd, const char *path, mode_t mode);

DESCRIPTION
       The mkfifo() function shall create a new FIFO special file named by the
       pathname pointed to by path.  The file permission bits of the new  FIFO
       shall  be  initialized from mode.  The file permission bits of the mode
       argument shall be modified by the process' file creation mask.

       When bits in mode other than the file  permission  bits	are  set,  the
       effect is implementation-defined.

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

       The FIFO's user ID shall be set to the process' effective user ID.  The
       FIFO's group ID shall be set to the group ID of the parent directory or
       to the effective group ID of the process. Implementations shall provide
       a  way  to initialize the FIFO's group ID to the group ID of the parent
       directory. Implementations may, but need not,  provide  an  implementa‐
       tion-defined  way  to  initialize  the FIFO's group ID to the effective
       group ID of the calling process.

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

       The mkfifoat() function shall be equivalent to  the  mkfifo()  function
       except  in  the case where path specifies a relative path. In this case
       the newly created FIFO is created 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 per‐
       missions of the directory underlying the file descriptor. If  the  file
       descriptor was opened with O_SEARCH, the function shall not perform the
       check.

       If mkfifoat() 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 mkfifo().

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, no FIFO shall 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 of the FIFO
	      to be created.

       EEXIST The named file already exists.

       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.

       EROFS  The named file resides on a read-only file system.

       The mkfifoat() 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 File
       The  following  example	shows  how  to	create	a  FIFO	  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>

	   int status;
	   ...
	   status = mkfifo("/home/cnd/mod_done", S_IWUSR | S_IRUSR |
	       S_IRGRP | S_IROTH);

APPLICATION USAGE
       None.

RATIONALE
       The syntax of this function is intended to maintain compatibility  with
       historical   implementations  of	 mknod().   The	 latter	 function  was
       included in the 1984 /usr/group standard but only for use  in  creating
       FIFO  special  files. The mknod() function was originally excluded from
       the POSIX.1‐1988 standard as  implementation-defined  and  replaced  by
       mkdir()	and mkfifo().  The mknod() function is now included for align‐
       ment with the Single UNIX Specification.

       The POSIX.1‐1990 standard required that the group ID of a newly created
       FIFO 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 FIFO is created, or determine under what	condi‐
       tions the implementation will set the desired group ID.

       The purpose of the mkfifoat() function is to create a FIFO special file
       in directories other than the current working directory	without	 expo‐
       sure  to	 race  conditions.  Any	 part  of  the path of a file could be
       changed in parallel to a call to	 mkfifo(),  resulting  in  unspecified
       behavior.  By  opening  a  file descriptor for the target directory and
       using the mkfifoat() function it can be guaranteed that the newly  cre‐
       ated FIFO is located relative to the desired directory.

FUTURE DIRECTIONS
       None.

SEE ALSO
       chmod(), mknod(), umask()

       The    Base   Definitions   volume   of	 POSIX.1‐2008,	 <sys_stat.h>,
       <sys_types.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			    MKFIFO(3P)
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