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.\" SPDX-License-Identifier: Linux-man-pages-1-para
.\"
.\" This man page is Copyright (C) 1999 Claus Fischer.
.\"
.\" 990620 - page created - aeb@cwi.nl
.\"
.TH fifo 7 2023-07-15 "Linux man-pages 6.05.01"
.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.
.PP
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.
.PP
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.
.PP
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).
.PP
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.
.PP
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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