(number)
The file mode creation mask is initialized to this value. If not
specified, the mask will be initialized to 022.
useradd and newusers use this
mask to set the mode of the home directory they create if
is not set.
It is also used by login to define users' initial
umask. Note that this mask can be overridden by the user's GECOS
line (if is set) or by the
specification of a limit with the K identifier
in limits5.
It is also used by pam_umask as the default umask
value.