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 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)
Linux Man Page 20 Jun 1999 1