Umask sets the process's file mode creation mask to numask and returns the previous value of the mask. The low-order 9 bits of numask are
used whenever a file is created, clearing corresponding bits in the file mode (see chmod(2)). This clearing allows each user to restrict
the default access to his files.
The value is initially 022 (write access for owner only). The mask is inherited by child processes.
The previous value of the file mode mask is returned by the call.