mkfifo(3p) — Linux manual page

PROLOG | NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | EXAMPLES | APPLICATION USAGE | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT

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

SYNOPSIS         top

       #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         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 [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         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.

       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         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);

APPLICATION USAGE         top

       None.

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.

FUTURE DIRECTIONS         top

       None.

SEE ALSO         top

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

       The Base Definitions volume of POSIX.1‐2017, fcntl.h(0p),
       sys_stat.h(0p), sys_types.h(0p)

COPYRIGHT         top

       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(3P)

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