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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

SYNOPSIS

       #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);

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
       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().

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 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}.

       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  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.

FUTURE DIRECTIONS

       None.

SEE ALSO

       chmod(), mknod(), umask()

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

COPYRIGHT

       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 .