FIFO(7)                   (2017-11-26)                    FIFO(7)

     NAME
          fifo - first-in first-out special file, named pipe

     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.

          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.

          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 ENXIO (no such device or address) unless the
          other end has already been opened.

          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 communi-
          cate with itself should be very careful to avoid deadlocks.

     NOTES
          For details of the semantics of I/O on FIFOs, see pipe(7).

          When a process tries to write to a FIFO that is not opened
          for read on the other side, the process is sent a SIGPIPE
          signal.

          FIFO special files can be created by mkfifo(3), and are
          indicated by ls -l with the file type aqpaq.

     SEE ALSO
          mkfifo(1), open(2), pipe(2), sigaction(2), signal(2),
          socketpair(2), mkfifo(3), pipe(7)

     COLOPHON
          This page is part of release 5.10 of the Linux man-pages
          project.  A description of the project, information about

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     FIFO(7)                   (2017-11-26)                    FIFO(7)

          reporting bugs, and the latest version of this page, can be
          found at https://www.kernel.org/doc/man-pages/.

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