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 nonblocking 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 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.

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 sig-
       nal.

       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 3.25 of the Linux man-pages project.  A description of the project,  and  information  about
       reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.



Linux                                                      2008-12-03                                                    FIFO(7)