umask - set file creation mode mask
mode_t umask(mode_t mask)
Umask sets the process's file mode creation mask to mask and returns the
previous value of the mask. The low-order 9 bits of mask 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.
chmod(2), mknod(2), open(2).