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mkfifo.3p (8226B)

'\" et
.TH MKFIFO "3P" 2017 "IEEE/The Open Group" "POSIX Programmer's Manual"
.\"
.SH PROLOG
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.
.\"
.SH NAME
mkfifo, mkfifoat
\(em make a FIFO special file
.SH SYNOPSIS
.LP
.nf
#include <sys/stat.h>
.P
int mkfifo(const char *\fIpath\fP, mode_t \fImode\fP);
.P
#include <fcntl.h>
.P
int mkfifoat(int \fIfd\fP, const char *\fIpath\fP, mode_t \fImode\fP);
.fi
.SH DESCRIPTION
The
\fImkfifo\fR()
function shall create a new FIFO special file named by the pathname
pointed to by
.IR path .
The file permission bits of the new FIFO shall be initialized from
.IR mode .
The file permission bits of the
.IR mode
argument shall be modified by the process' file creation mask.
.P
When bits in
.IR mode
other than the file permission bits are set, the effect is
implementation-defined.
.P
If
.IR path
names a symbolic link,
\fImkfifo\fR()
shall fail and set
.IR errno
to
.BR [EEXIST] .
.P
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.
.P
Upon successful completion,
\fImkfifo\fR()
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.
.P
The
\fImkfifoat\fR()
function shall be equivalent to the
\fImkfifo\fR()
function except in the case where
.IR path
specifies a relative path. In this case the newly created FIFO is
created relative to the directory associated with the file descriptor
.IR 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.
.P
If
\fImkfifoat\fR()
is passed the special value AT_FDCWD in the
.IR fd
parameter, the current working directory shall be used and the behavior
shall be identical to a call to
\fImkfifo\fR().
.SH "RETURN VALUE"
Upon successful completion, these functions shall return 0.
Otherwise, these functions shall return \-1 and set
.IR errno
to indicate the error. If \-1 is returned, no FIFO shall be created.
.SH ERRORS
These functions shall fail if:
.TP
.BR 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
.BR EEXIST
The named file already exists.
.TP
.BR ELOOP
A loop exists in symbolic links encountered during resolution of the
.IR path
argument.
.TP
.BR ENAMETOOLONG
.br
The length of a component of a pathname is longer than
{NAME_MAX}.
.TP
.BR ENOENT
A component of the path prefix of
.IR path
does not name an existing file or
.IR path
is an empty string.
.TP
.BR ENOENT " or " ENOTDIR
.br
The
.IR path
argument contains at least one non-\c
<slash>
character and ends with one or more trailing
<slash>
characters. If
.IR path
without the trailing
<slash>
characters would name an existing file, an
.BR [ENOENT] 
error shall not occur.
.TP
.BR ENOSPC
The directory that would contain the new file cannot be extended or the
file system is out of file-allocation resources.
.TP
.BR ENOTDIR
A component of the path prefix names an existing file that is neither
a directory nor a symbolic link to a directory.
.TP
.BR EROFS
The named file resides on a read-only file system.
.P
The
\fImkfifoat\fR()
function shall fail if:
.TP
.BR EACCES
The access mode of the open file description associated with
.IR fd
is not O_SEARCH and the permissions of the directory underlying
.IR fd
do not permit directory searches.
.TP
.BR EBADF
The
.IR path
argument does not specify an absolute path and the
.IR fd
argument is neither AT_FDCWD nor a valid file descriptor open
for reading or searching.
.TP
.BR ENOTDIR
The
.IR path
argument is not an absolute path and
.IR fd
is a file descriptor associated with a non-directory file.
.P
These functions may fail if:
.TP
.BR ELOOP
More than
{SYMLOOP_MAX}
symbolic links were encountered during resolution of the
.IR path
argument.
.TP
.BR ENAMETOOLONG
.br
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}.
.LP
.IR "The following sections are informative."
.SH EXAMPLES
.SS "Creating a FIFO File"
.P
The following example shows how to create a FIFO file named
.BR /home/cnd/mod_done ,
with read/write permissions for owner, and with read permissions for
group and others.
.sp
.RS 4
.nf
#include <sys/types.h>
#include <sys/stat.h>
.P
int status;
\&...
status = mkfifo("/home/cnd/mod_done", S_IWUSR | S_IRUSR |
    S_IRGRP | S_IROTH);
.fi
.P
.RE
.SH "APPLICATION USAGE"
None.
.SH RATIONALE
The syntax of this function is intended to maintain compatibility with
historical implementations of
\fImknod\fR().
The latter function was included in the 1984 /usr/group standard but only for use in
creating FIFO special files. The
\fImknod\fR()
function was originally excluded from the POSIX.1\(hy1988 standard as
implementation-defined and replaced by
\fImkdir\fR()
and
\fImkfifo\fR().
The
\fImknod\fR()
function is now included for alignment with the Single UNIX Specification.
.P
The POSIX.1\(hy1990 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\(hy2 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\fR()
to set the group ID after the FIFO is created, or determine under
what conditions the implementation will set the desired group ID.
.P
The purpose of the
\fImkfifoat\fR()
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
\fImkfifo\fR(),
resulting in unspecified behavior. By opening a file descriptor for
the target directory and using the
\fImkfifoat\fR()
function it can be guaranteed that the newly created FIFO is located
relative to the desired directory.
.SH "FUTURE DIRECTIONS"
None.
.SH "SEE ALSO"
.IR "\fIchmod\fR\^(\|)",
.IR "\fImknod\fR\^(\|)",
.IR "\fIumask\fR\^(\|)"
.P
The Base Definitions volume of POSIX.1\(hy2017,
.IR "\fB<fcntl.h>\fP",
.IR "\fB<sys_stat.h>\fP",
.IR "\fB<sys_types.h>\fP"
.\"
.SH COPYRIGHT
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 .
.PP
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 .