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
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
Upon successful completion, mkfifo() shall mark for update the
st_atime, st_ctime, and st_mtime fields of the file.
Also, the st_ctime and st_mtime fields of the directory that
contains the new entry shall be marked for update.
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.
Portions of this text are reprinted and reproduced in electronic form from IEEE
Std 1003.1, 2003 Edition, Standard for Information Technology -- Portable
Operating System Interface (POSIX), The Open Group Base Specifications Issue
6, Copyright (C) 2001-2003 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