.\" This manpage is Copyright (C) 1995 James R. Van Zandt <jrv@vanzandt.mv.com>

.\" and Copyright (C) 2006, 2014 Michael Kerrisk

.\"

.\" %%%LICENSE_START(VERBATIM)

.\" Permission is granted to make and distribute verbatim copies of this

.\" manual provided the copyright notice and this permission notice are

.\" preserved on all copies.

.\"

.\" Permission is granted to copy and distribute modified versions of this

.\" manual under the conditions for verbatim copying, provided that the

.\" entire resulting derived work is distributed under the terms of a

.\" permission notice identical to this one.

.\"

.\" Since the Linux kernel and libraries are constantly changing, this

.\" manual page may be incorrect or out-of-date.  The author(s) assume no

.\" responsibility for errors or omissions, or for damages resulting from

.\" the use of the information contained herein.  The author(s) may not

.\" have taken the same level of care in the production of this manual,

.\" which is licensed free of charge, as they might when working

.\" professionally.

.\"

.\" Formatted or processed versions of this manual, if unaccompanied by

.\" the source, must acknowledge the copyright and authors of this work.

.\" %%%LICENSE_END

.\"

.\" changed section from 2 to 3, aeb, 950919

.\"

.TH MKFIFO 3 2017-09-15 "GNU" "Linux Programmer's Manual"

.SH NAME

mkfifo, mkfifoat \- make a FIFO special file (a named pipe)

.SH SYNOPSIS

.nf

.B #include <sys/types.h>

.B #include <sys/stat.h>

.PP

.BI "int mkfifo(const char *" pathname ", mode_t " mode );

.BR "#include <fcntl.h>           " "/* Definition of AT_* constants */"

.B #include <sys/stat.h>

.PP

.BI "int mkfifoat(int " dirfd ", const char *" pathname ", mode_t " mode );

.fi

.PP

.in -4n

Feature Test Macro Requirements for glibc (see

.BR feature_test_macros (7)):

.in

.PP

.BR mkfifoat ():

.PD 0

.ad l

.RS 4

.TP 4

Since glibc 2.10:

_POSIX_C_SOURCE\ >=\ 200809L

.TP

Before glibc 2.10:

_ATFILE_SOURCE

.RE

.ad

.PD

.SH DESCRIPTION

.BR mkfifo ()

makes a FIFO special file with name \fIpathname\fP.

\fImode\fP specifies the FIFO's permissions.

It is modified by the

process's \fBumask\fP in the usual way: the permissions of the created

file are \fB(\fP\fImode\fP\fB & ~umask)\fP.

.PP

A FIFO special file is similar to a pipe, except that it is created

in a different way.

Instead of being an anonymous communications

channel, a FIFO special file is entered into the filesystem by

calling

.BR mkfifo ().

.PP

Once you have created a FIFO special file in this way, any process can

open it for reading or writing, in the same way as an ordinary file.

However, it has to be open at both ends simultaneously before you can

proceed to do any input or output operations on it.

Opening a FIFO for reading normally blocks until some

other process opens the same FIFO for writing, and vice versa.

See

.BR fifo (7)

for nonblocking handling of FIFO special files.

.SS mkfifoat()

The

.BR mkfifoat ()

function operates in exactly the same way as

.BR mkfifo (),

except for the differences described here.

.PP

If the pathname given in

.I pathname

is relative, then it is interpreted relative to the directory

referred to by the file descriptor

.I dirfd

(rather than relative to the current working directory of

the calling process, as is done by

.BR mkfifo ()

for a relative pathname).

.PP

If

.I pathname

is relative and

.I dirfd

is the special value

.BR AT_FDCWD ,

then

.I pathname

is interpreted relative to the current working

directory of the calling process (like

.BR mkfifo ()).

.PP

If

.I pathname

is absolute, then

.I dirfd

is ignored.

.SH RETURN VALUE

On success

.BR mkfifo ()

and

.BR mkfifoat ()

return 0.

In the case of an error, \-1 is returned (in which case, \fIerrno\fP

is set appropriately).

.SH ERRORS

.TP

.B EACCES

One of the directories in \fIpathname\fP did not allow search

(execute) permission.

.TP

.B EDQUOT

The user's quota of disk blocks or inodes on the filesystem has been

exhausted.

.TP

.B EEXIST

\fIpathname\fP already exists.

This includes the case where

.I pathname

is a symbolic link, dangling or not.

.TP

.B ENAMETOOLONG

Either the total length of \fIpathname\fP is greater than

\fBPATH_MAX\fP, or an individual filename component has a length

greater than \fBNAME_MAX\fP.

In the GNU system, there is no imposed

limit on overall filename length, but some filesystems may place

limits on the length of a component.

.TP

.B ENOENT

A directory component in \fIpathname\fP does not exist or is a

dangling symbolic link.

.TP

.B ENOSPC

The directory or filesystem has no room for the new file.

.TP

.B ENOTDIR

A component used as a directory in \fIpathname\fP is not, in fact, a

directory.

.TP

.B EROFS

\fIpathname\fP refers to a read-only filesystem.

.PP

The following additional errors can occur for

.BR mkfifoat ():

.TP

.B EBADF

.I dirfd

is not a valid file descriptor.

.TP

.B ENOTDIR

.I pathname

is a relative path and

.I dirfd

is a file descriptor referring to a file other than a directory.

.SH VERSIONS

.BR mkfifoat ()

was added to glibc in version 2.4.

It is implemented using

.BR mknodat (2),

available on Linux since kernel 2.6.16.

.SH ATTRIBUTES

For an explanation of the terms used in this section, see

.BR attributes (7).

.TS

allbox;

lbw20 lb lb

l l l.

Interface	Attribute	Value

T{

.BR mkfifo (),

.BR mkfifoat ()

T}	Thread safety	MT-Safe

.TE

.SH CONFORMING TO

.BR mkfifo ():

POSIX.1-2001, POSIX.1-2008.

.PP

.BR mkfifoat ():

POSIX.1-2008.

.SH SEE ALSO

.BR mkfifo (1),

.BR close (2),

.BR open (2),

.BR read (2),

.BR stat (2),

.BR umask (2),

.BR write (2),

.BR fifo (7)

.SH COLOPHON

This page is part of release 4.15 of the Linux

.I man-pages

project.

A description of the project,

information about reporting bugs,

and the latest version of this page,

can be found at

\%https://www.kernel.org/doc/man\-pages/.