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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 file system.  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 file system.  Thus, the FIFO special file has no contents on the
       file system; the file system entry merely serves as a  reference  point
       so that processes can access the pipe using a name in the file system.

       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 will succeed even if no-one has opened on the write side
       yet, opening for write only will fail 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
       communicate with itself should be very careful to avoid deadlocks.

NOTES

       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 'p'.

SEE ALSO

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

COLOPHON

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