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.\" Copyright, the authors of the Linux man-pages project
.\"
.\" SPDX-License-Identifier: Linux-man-pages-1-para
.\"
.TH fifo 7 (date) "Linux man-pages (unreleased)"
.SH NAME
fifo \- first-in first-out special file, named pipe
.SH DESCRIPTION
A FIFO special file (a named pipe) is similar to a pipe,
except that it is accessed as part of the filesystem.
It can be opened by multiple processes for reading or
writing.
When processes are exchanging data via the FIFO,
the kernel passes all data internally without writing it
to the filesystem.
Thus,
the FIFO special file has no contents on the filesystem;
the filesystem entry merely serves as a reference point
so that processes can access the pipe
using a name in the filesystem.
.P
The kernel maintains exactly one pipe object for each
FIFO special file that is opened by at least one process.
The FIFO must be opened on both ends (reading and writing)
before data can be passed.
Normally,
opening the FIFO blocks
until the other end is opened also.
.P
A process can open a FIFO in nonblocking mode.
In this case,
opening for read-only succeeds
even if no one has opened on the write side yet
and opening for write-only fails with
.B ENXIO
(no such device or address)
unless the other end has already been opened.
.P
Under Linux,
opening a FIFO for read and write will succeed
both in blocking and nonblocking mode.
POSIX leaves this behavior undefined.
This can be used to open a FIFO for writing
while there are no readers available.
A process that uses both ends of the connection
in order to communicate with itself
should be very careful to avoid deadlocks.
.SH NOTES
For details of the semantics of I/O on FIFOs, see
.BR pipe (7).
.P
When a process tries to write to a FIFO
that is not opened for read on the other side,
the process is sent a
.B SIGPIPE
signal.
.P
FIFO special files can be created by
.BR mkfifo (3),
and are indicated by
.I ls\~\-l
with the file type \[aq]p\[aq].
.SH SEE ALSO
.BR mkfifo (1),
.BR open (2),
.BR pipe (2),
.BR sigaction (2),
.BR signal (2),
.BR socketpair (2),
.BR mkfifo (3),
.BR pipe (7)
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