I am working in a lab where we are running Linux (Debian and Ubuntu). Usernames and group names are handled by NIS and yp. We have some common users that everybody has acces
Both Debian and Ubuntu ship with pam_umask. This allows you to configure umask in /etc/login.defs and have them apply system-wide, regardless of how a user logs in.
To enable it, you may need to add a line to /etc/pam.d/common-session reading
session optional pam_umask.so
or it may already be enabled. Then edit /etc/login.defs and change the UMASK line to
UMASK 002
(the default is 022).
Note that users may still override umask in their own ~/.profile or ~/.bashrc or similar, but (at least on new Debian and Ubuntu installations) there shouldn't be any overriding of umask in /etc/profile or /etc/bash.bashrc. (If there are, just remove them.)