umask() sets PHP's umask to
mask & 0777 and returns the old
umask. When PHP is being used as a server module, the umask
is restored when each request is finished.
umask() without arguments simply returns the current umask.
Note: Avoid using this function in multithreaded webservers. It is better to change the file permissions with chmod() after creating the file. Using umask() can lead to unexpected behavior of concurrently running scripts and the webserver itself because they all use the same umask.