mirror of https://github.com/mkerrisk/man-pages
76 lines
2.3 KiB
Groff
76 lines
2.3 KiB
Groff
.\" This man page is Copyright (C) 1999 Claus Fischer.
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.\"
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.\" %%%LICENSE_START(VERBATIM_ONE_PARA)
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.\" Permission is granted to distribute possibly modified copies
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.\" of this page provided the header is included verbatim,
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.\" and in case of nontrivial modification author and date
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.\" of the modification is added to the header.
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.\" %%%LICENSE_END
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.\"
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.\" 990620 - page created - aeb@cwi.nl
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.\"
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.TH FIFO 7 2017-11-26 "Linux" "Linux Programmer's Manual"
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.SH NAME
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fifo \- first-in first-out special file, named pipe
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.SH DESCRIPTION
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A FIFO special file (a named pipe) is similar to a pipe,
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except that it is accessed as part of the filesystem.
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It can be opened by multiple processes for reading or
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writing.
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When processes are exchanging data via the FIFO,
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the kernel passes all data internally without writing it
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to the filesystem.
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Thus, the FIFO special file has no
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contents on the filesystem; the filesystem entry merely
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serves as a reference point so that processes can access
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the pipe using a name in the filesystem.
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.PP
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The kernel maintains exactly one pipe object for each
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FIFO special file that is opened by at least one process.
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The FIFO must be opened on both ends (reading and writing)
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before data can be passed.
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Normally, opening the FIFO blocks
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until the other end is opened also.
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.PP
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A process can open a FIFO in nonblocking mode.
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In this
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case, opening for read-only succeeds even if no one has
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opened on the write side yet and opening for write-only
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fails with
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.B ENXIO
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(no such device or address) unless the other
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end has already been opened.
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.PP
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Under Linux, opening a FIFO for read and write will succeed
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both in blocking and nonblocking mode.
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POSIX leaves this
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behavior undefined.
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This can be used to open a FIFO for
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writing while there are no readers available.
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A process
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that uses both ends of the connection in order to communicate
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with itself should be very careful to avoid deadlocks.
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.SH NOTES
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For details of the semantics of I/O on FIFOs, see
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.BR pipe (7).
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.PP
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When a process tries to write to a FIFO that is not opened
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for read on the other side, the process is sent a
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.B SIGPIPE
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signal.
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.PP
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FIFO special files can be created by
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.BR mkfifo (3),
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and are indicated by
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.IR "ls\ \-l"
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with the file type \(aqp\(aq.
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.SH SEE ALSO
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.BR mkfifo (1),
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.BR open (2),
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.BR pipe (2),
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.BR sigaction (2),
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.BR signal (2),
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.BR socketpair (2),
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.BR mkfifo (3),
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.BR pipe (7)
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