man7/fifo.7

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  12 .TH FIFO 7 2008-12-03 "Linux" "Linux Programmer's Manual"
  13 .SH NAME
  14 fifo \- first-in first-out special file, named pipe
  15 .SH DESCRIPTION
  16 A FIFO special file (a named pipe) is similar to a pipe,
  17 except that it is accessed as part of the filesystem.
  18 It can be opened by multiple processes for reading or
  19 writing.
  20 When processes are exchanging data via the FIFO,
  21 the kernel passes all data internally without writing it
  22 to the filesystem.
  23 Thus, the FIFO special file has no
  24 contents on the filesystem; the filesystem entry merely
  25 serves as a reference point so that processes can access
  26 the pipe using a name in the filesystem.
  27 .PP
  28 The kernel maintains exactly one pipe object for each
  29 FIFO special file that is opened by at least one process.
  30 The FIFO must be opened on both ends (reading and writing)
  31 before data can be passed.
  32 Normally, opening the FIFO blocks
  33 until the other end is opened also.
  34 .PP
  35 A process can open a FIFO in nonblocking mode.
  36 In this
  37 case, opening for read-only will succeed even if no-one has
  38 opened on the write side yet and opening for write-only will
  39 fail with
  40 .B ENXIO
  41 (no such device or address) unless the other
  42 end has already been opened.
  43 .PP
  44 Under Linux, opening a FIFO for read and write will succeed
  45 both in blocking and nonblocking mode.
  46 POSIX leaves this
  47 behavior undefined.
  48 This can be used to open a FIFO for
  49 writing while there are no readers available.
  50 A process
  51 that uses both ends of the connection in order to communicate
  52 with itself should be very careful to avoid deadlocks.
  53 .SH NOTES
  54 When a process tries to write to a FIFO that is not opened
  55 for read on the other side, the process is sent a
  56 .B SIGPIPE
  57 signal.
  58
  59 FIFO special files can be created by
  60 .BR mkfifo (3),
  61 and are indicated by
  62 .IR "ls\ \-l"
  63 with the file type \(aqp\(aq.
  64 .SH SEE ALSO
  65 .BR mkfifo (1),
  66 .BR open (2),
  67 .BR pipe (2),
  68 .BR sigaction (2),
  69 .BR signal (2),
  70 .BR socketpair (2),
  71 .BR mkfifo (3),
  72 .BR pipe (7)