posix_mkfifo() creates a special FIFO file which exists in the file system and acts as a bidirectional communication endpoint for processes.
The second parameter mode has to be given in octal notation (e.g. 0644). The permission of the newly created FIFO also depends on the setting of the current umask(). The permissions of the created file are (mode & ~umask).
Note: When safe mode is enabled, PHP checks whether the directory in which you are about to operate has the same UID (owner) as the script that is being executed.