09-03-2015
Quote:
Originally Posted by
bakunin
Thats not entirely correct. When /dev/null is read it produces a EOF-marker and this way it is made sure that the file to be shortened is well-formed (i.e. contains a end-of-file sign).
It's not
write-ing anything which truncates the file here -- just
open-ing it with mode
O_TRUNC is enough, as is done by > but not >>.
I know really early versions of DOS used to use end-of-file symbols, but I've never observed such a thing in UNIX before. Is that an Oracle thing? I would have thought that'd be handled internally by the filesystem driver. Do you have more information?
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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 multi-
ple processes for reading or writing. When processes are exchanging data via the FIFO, the kernel passes all data internally without writ-
ing 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 Man Page 1999-06-20 FIFO(4)