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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 non-blocking mode. In this case, opening
       for read only will succeed even if noone 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 non-blocking mode. POSIX leaves this behaviour 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 specially
       indicated in ls -l.

SEE ALSO

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