mkfifo(3p) — Linux manual page


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

PROLOG         top

       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         top

       mkfifo, mkfifoat — make a FIFO special file relative to directory
       file descriptor

SYNOPSIS         top

       #include <sys/stat.h>

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

DESCRIPTION         top

       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

       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         top

       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         top

       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.

              The length of a component of a pathname is longer than

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

              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

              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.

              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.

              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         top

   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);



RATIONALE         top

       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.



SEE ALSO         top

       chmod(3p), mknod(3p), umask(3p)

       The Base Definitions volume of POSIX.1‐2008, sys_stat.h(0p),

COPYRIGHT         top

       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 .

       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 .

IEEE/The Open Group                 2013                          MKFIFO(3P)

Pages that refer to this page: sys_stat.h(0p)mkfifo(1p)pax(1p)chmod(3p)mknod(3p)mknodat(3p)umask(3p)