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

   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 and 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.


   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'.


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


   This page is part of release 4.09 of the Linux  man-pages  project.   A
   description  of  the project, information about reporting bugs, and the
   latest    version    of    this    page,    can     be     found     at


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