FIFO(7) Linux Programmer's Manual FIFO(7)
fifo - first-in first-out special file, named pipe
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 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 nonblock-
ing 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 con-
nection in order to communicate with itself should be very careful to avoid deadlocks.
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
mkfifo(1), open(2), pipe(2), sigaction(2), signal(2), socketpair(2), mkfifo(3), pipe(7)
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Linux 2008-12-03 FIFO(7)