This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface

       None.

       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1-2017, Standard
       for  Information  Technology  --  Portable  Operating  System  Interface  (POSIX),  The  Open  Group Base
       Specifications Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of Electrical  and  Electronics
       Engineers, Inc and The Open Group.  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.opengroup.org/unix/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.kernel.org/doc/man-pages/reporting_bugs.html .

IEEE/The Open Group                                   2017                                        MKFIFO(3POSIX)

       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  implementation-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 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.

       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 access mode of
       the open file description associated with the file descriptor is not O_SEARCH, the function  shall  check
       whether  directory  searches  are permitted using the current permissions of the directory underlying the
       file descriptor. If the access mode is 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().

       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 without the trailing <slash> characters would name 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 The  access  mode  of  the  open  file  description  associated  with  fd  is not 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 resolution of a symbolic link produced an
              intermediate result with a length that exceeds {PATH_MAX}.

       Thefollowingsectionsareinformative.

CreatingaFIFOFile
       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);

       None.

       mkfifo, mkfifoat — make a FIFO special file

       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.

       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
       alignment 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
       implementations  provide  a  way to have the group ID be set to the group ID of the containing directory,
       but did not prohibit implementations also supporting a way to set the group ID to the effective group  ID
       of  the  creating  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 conditions 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 exposure 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
       created FIFO is located relative to the desired directory.

       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.

chmod(), mknod(), umask()

       The Base Definitions volume of POSIX.1‐2017, <fcntl.h>, <sys_stat.h>, <sys_types.h>

       #include <sys/stat.h>

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

       #include <fcntl.h>

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