man-pages/man3p/mkfifo.3p

.\" Copyright (c) 2001-2003 The Open Group, All Rights Reserved 
.TH "MKFIFO" P 2003 "IEEE/The Open Group" "POSIX Programmer's Manual"
.\" mkfifo 
.SH NAME
mkfifo \- make a FIFO special file
.SH SYNOPSIS
.LP
\fB#include <sys/stat.h>
.br
.sp
int mkfifo(const char *\fP\fIpath\fP\fB, mode_t\fP \fImode\fP\fB);
.br
\fP
.SH DESCRIPTION
.LP
The \fImkfifo\fP() function shall create a new FIFO special file named
by the pathname pointed to by \fIpath\fP. The file
permission bits of the new FIFO shall be initialized from \fImode\fP.
The file permission bits of the \fImode\fP argument shall
be modified by the process' file creation mask.
.LP
When bits in \fImode\fP other than the file permission bits are set,
the effect is implementation-defined.
.LP
If \fIpath\fP names a symbolic link, \fImkfifo\fP() shall fail and
set \fIerrno\fP to [EEXIST].
.LP
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.
.LP
Upon successful completion, \fImkfifo\fP() shall mark for update the
\fIst_atime\fP, \fIst_ctime\fP, and \fIst_mtime\fP
fields of the file. Also, the \fIst_ctime\fP and \fIst_mtime\fP fields
of the directory that contains the new entry shall be
marked for update.
.SH RETURN VALUE
.LP
Upon successful completion, 0 shall be returned. Otherwise, -1 shall
be returned, no FIFO shall be created, and \fIerrno\fP
shall be set to indicate the error.
.SH ERRORS
.LP
The \fImkfifo\fP() function shall fail if:
.TP 7
.B 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.
.TP 7
.B EEXIST
The named file already exists.
.TP 7
.B ELOOP
A loop exists in symbolic links encountered during resolution of the
\fIpath\fP argument.
.TP 7
.B ENAMETOOLONG
The length of the \fIpath\fP argument exceeds {PATH_MAX} or a pathname
component is longer than {NAME_MAX}.
.TP 7
.B ENOENT
A component of the path prefix specified by \fIpath\fP does not name
an existing directory or \fIpath\fP is an empty
string.
.TP 7
.B ENOSPC
The directory that would contain the new file cannot be extended or
the file system is out of file-allocation resources.
.TP 7
.B ENOTDIR
A component of the path prefix is not a directory.
.TP 7
.B EROFS
The named file resides on a read-only file system.
.sp
.LP
The \fImkfifo\fP() function may fail if:
.TP 7
.B ELOOP
More than {SYMLOOP_MAX} symbolic links were encountered during resolution
of the \fIpath\fP argument.
.TP 7
.B ENAMETOOLONG
As a result of encountering a symbolic link in resolution of the \fIpath\fP
argument, the length of the substituted pathname
string exceeded {PATH_MAX}.
.sp
.LP
\fIThe following sections are informative.\fP
.SH EXAMPLES
.SS Creating a FIFO File
.LP
The following example shows how to create a FIFO file named \fB/home/cnd/mod_done\fP,
with read/write permissions for owner,
and with read permissions for group and others.
.sp
.RS
.nf

\fB#include <sys/types.h>
#include <sys/stat.h>
.sp

int status;
\&...
status = mkfifo("/home/cnd/mod_done", S_IWUSR | S_IRUSR |
    S_IRGRP | S_IROTH);
\fP
.fi
.RE
.SH APPLICATION USAGE
.LP
None.
.SH RATIONALE
.LP
The syntax of this function is intended to maintain compatibility
with historical implementations of \fImknod\fP(). The latter function
was included in the 1984 /usr/group standard but only for use in
creating FIFO special files. The \fImknod\fP() function was originally
excluded from the
POSIX.1-1988 standard as implementation-defined and replaced by \fImkdir\fP()
and
\fImkfifo\fP(). The \fImknod\fP() function is now included for alignment
with the Single
UNIX Specification.
.LP
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 \fIchown\fP() to set the group ID
after the FIFO is created,
or determine under what conditions the implementation will set the
desired group ID.
.SH FUTURE DIRECTIONS
.LP
None.
.SH SEE ALSO
.LP
\fIumask\fP() , the Base Definitions volume of IEEE\ Std\ 1003.1-2001,
\fI<sys/stat.h>\fP, \fI<sys/types.h>\fP
.SH 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 .