man4/fifo.4

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   9 .TH FIFO 4 1999-06-20 "Linux" "Linux Programmer's Manual"
  10 .SH NAME
  11 fifo \- first-in first-out special file, named pipe
  12 .SH DESCRIPTION
  13 A FIFO special file (a named pipe) is similar to a pipe,
  14 except that it is accessed as part of the file system.
  15 It can be opened by multiple processes for reading or
  16 writing. When processes are exchanging data via the FIFO,
  17 the kernel passes all data internally without writing it
  18 to the file system. Thus, the FIFO special file has no
  19 contents on the file system, the file system entry merely
  20 serves as a reference point so that processes can access
  21 the pipe using a name in the file system.
  22 .PP
  23 The kernel maintains exactly one pipe object for each
  24 FIFO special file that is opened by at least one process.
  25 The FIFO must be opened on both ends (reading and writing)
  26 before data can be passed. Normally, opening the FIFO blocks
  27 until the other end is opened also.
  28 .PP
  29 A process can open a FIFO in non-blocking mode. In this
  30 case, opening for read only will succeed even if noone has
  31 opened on the write side yet; opening for write only will
  32 fail with ENXIO (no such device or address) unless the other
  33 end has already been opened.
  34 .PP
  35 Under Linux, opening a FIFO for read and write will succeed
  36 both in blocking and non-blocking mode. POSIX leaves this
  37 behaviour undefined. This can be used to open a FIFO for
  38 writing while there are no readers available. A process
  39 that uses both ends of the connection in order to communicate
  40 with itself should be very careful to avoid deadlocks.
  41 .SH NOTES
  42 When a process tries to write to a FIFO that is not opened
  43 for read on the other side, the process is sent a SIGPIPE
  44 signal.
  45
  46 FIFO special files can be created by
  47 .BR mkfifo (3),
  48 and are specially indicated in
  49 .IR "ls -l" .
  50 .SH "SEE ALSO"
  51 .BR mkfifo (1),
  52 .BR open (2),
  53 .BR pipe (2),
  54 .BR sigaction (2),
  55 .BR signal (2),
  56 .BR socketpair (2),
  57 .BR mkfifo (3)