man > fifo(7)

fifo(7)                           Miscellaneous Information 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 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  succeeds
       even  if  no one has opened on the write side yet and opening for write-only fails 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 or‐
       der to communicate with itself should be very careful to avoid deadlocks.

NOTES
       For details of the semantics of I/O on FIFOs, see pipe(7).

       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)

Linux man-pages 6.7                          2023-10-31                                      fifo(7)