MKFIFO(P) POSIX Programmer's Manual MKFIFO(P)NAMEmkfifo - make a FIFO special file
SYNOPSIS
#include <sys/stat.h>
int mkfifo(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 implementa‐
tion-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
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.
RETURN VALUE
Upon successful completion, 0 shall be returned. Otherwise, -1 shall be
returned, no FIFO shall be created, and errno shall be set to indicate
the error.
ERRORS
The mkfifo() function 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 the path argument exceeds {PATH_MAX} or a pathname
component is longer than {NAME_MAX}.
ENOENT A component of the path prefix specified by path does not name
an existing directory or path is an empty string.
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 is not a directory.
EROFS The named file resides on a read-only file system.
The mkfifo() function may fail if:
ELOOP More than {SYMLOOP_MAX} symbolic links were encountered during
resolution of the path argument.
ENAMETOOLONG
As a result of encountering a symbolic link in resolution of the
path argument, the length of the substituted pathname string
exceeded {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 spe‐
cial 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 implementa‐
tions provide a way to have the group ID be set to the group ID of the
containing directory, but did not prohibit implementations also sup‐
porting a way to set the group ID to the effective group ID of the cre‐
ating 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.
FUTURE DIRECTIONS
None.
SEE ALSOumask() , the Base Definitions volume of IEEE Std 1003.1-2001,
<sys/stat.h>, <sys/types.h>
COPYRIGHT
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 .
IEEE/The Open Group 2003 MKFIFO(P)
