mkfifo

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
       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 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 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
              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.1‐2008, <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
       Electrical 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.kernel.org/doc/man-pages/reporting_bugs.html .



IEEE/The Open Group                  2013                           MKFIFO(3P)