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FIFO(4)			   Linux Programmer's Manual		       FIFO(4)

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

       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 ad-
       dress) 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.

       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 indi-
       cated in	ls -l.

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

Linux Man Page			  1999-06-20			       FIFO(4)


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