There are several ways of creating a named pipe. The first two can be done directly from the shell.
mknod MYFIFO p mkfifo a=rw MYFIFO
The above two commands perform identical operations, with one exception. The mkfifo command provides a hook for altering the permissions on the FIFO file directly after creation. With mknod, a quick call to the chmod command will be necessary.
FIFO files can be quickly identified in a physical file system by the ``p'' indicator seen here in a long directory listing:
$ ls -l MYFIFO prw-r--r-- 1 root root 0 Dec 14 22:15 MYFIFO|
Also notice the vertical bar (``pipe sign'') located directly after the file name. Another great reason to run Linux, eh?
To create a FIFO in C, we can make use of the mknod() system call:
LIBRARY FUNCTION: mknod(); PROTOTYPE: int mknod( char *pathname, mode_t mode, dev_t dev); RETURNS: 0 on success, -1 on error: errno = EFAULT (pathname invalid) EACCES (permission denied) ENAMETOOLONG (pathname too long) ENOENT (invalid pathname) ENOTDIR (invalid pathname) (see man page for mknod for others) NOTES: Creates a filesystem node (file, device file, or FIFO)
mknod("/tmp/MYFIFO", S_IFIFO|0666, 0);
In this case, the file ``/tmp/MYFIFO'' is created as a FIFO file. The requested permissions are ``0666'', although they are affected by the umask setting as follows:
final_umask = requested_permissions & ~original_umask
A common trick is to use the umask() system call to temporarily zap the umask value:
umask(0); mknod("/tmp/MYFIFO", S_IFIFO|0666, 0);
In addition, the third argument to mknod() is ignored unless we are creating a device file. In that instance, it should specify the major and minor numbers of the device file.