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 writ­
       ing. 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  con­
       tents  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 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 suc­
       ceed 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  pro­
       cess  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)