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FIFO(7)                    Linux Programmer's Manual                   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 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 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 non-blocking mode.  POSIX
       leaves this behavior undefined.  This can be used to open a FIFO for writing while there are no readers  avail-
       able.  A process that uses both ends of the connection in order to communicate with itself should be very care-
       ful 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
       This  page  is part of release 3.22 of the Linux man-pages project.  A description of the project, and informa-
       tion about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.



Linux                             2008-12-03                           FIFO(7)