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fifo(4) - fifo, fifo - first-in first-out special file, named pipe - man 4 fifo

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



NAME
       fifo - first-in first-out special file(1,n), named(5,8) pipe(2,8)

DESCRIPTION
       A FIFO special file(1,n) (a named(5,8) pipe(2,8)) is similar to a pipe(2,8), except that it
       is accessed as part of the file(1,n) 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(1,n) system. Thus, the FIFO special file(1,n) has no contents on the
       file(1,n) system, the file(1,n) system entry merely serves as a  reference  point
       so  that processes can access(2,5) the pipe(2,8) using a name in(1,8) the file(1,n) system.

       The kernel maintains exactly one pipe(2,8) object for each FIFO special file(1,n)
       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(2,3,n) a FIFO in(1,8) non-blocking mode. In this case, opening
       for read(2,n,1 builtins) only will succeed even if(3,n) noone has opened on the  write(1,2)  side
       yet;  opening  for  write(1,2)  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(2,n,1 builtins) and write(1,2)  will  succeed  both  in(1,8)
       blocking  and non-blocking mode. POSIX leaves this behaviour undefined.
       This can be used to open(2,3,n) a FIFO for writing while there are no  readers
       available.  A process that uses both ends of the connection in(1,8) order to
       communicate with itself should be very careful to avoid deadlocks.

NOTES
       When a process tries to write(1,2) to a FIFO that is not opened for read(2,n,1 builtins)  on
       the other side, the process is sent a SIGPIPE signal.

       FIFO special files can be created by mkfifo(1,3)(3), and are specially indi-
       cated in(1,8) ls -l.

SEE ALSO
       mkfifo(1,3)(1), open(2,3,n)(2), pipe(2,8)(2),  sigaction(2),  signal(2,7)(2),  socketpair(2),
       mkfifo(1,3)(3)



Linux                             1999-06-20                           FIFO(4)

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