MKFIFO(P) MKFIFO(P)
NAME
mkfifo - 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 implementa-
tion-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 implemen-
tation-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 direc-
tory 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 imple-
mentations 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.
FUTURE DIRECTIONS
None.
SEE ALSO
umask() , 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 orig-
inal Standard can be obtained online at http://www.opengroup.org/unix/online.html .
POSIX 2003 MKFIFO(P)
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