The
umask()
routine sets the process's file mode creation mask to
numask
and returns the previous value of the mask.
The 9 low-order
access permission
bits of
numask
are used by system calls, including
open(2),
mkdir(2),
and
mkfifo(2),
to turn off corresponding bits
requested in file mode.
(See
chmod(2)).
This clearing allows each user to restrict the default access
to his files.
The default mask value is S_IWGRP|S_IWOTH (022, write access for the
owner only).
Child processes inherit the mask of the calling process.
