fifo - phpMan

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



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 refer-
       ence 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 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 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.

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 specially indicated in ls
       -l.

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



Linux                             1999-06-20                           FIFO(4)

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