I am using a private user group setup, i.e. a user foo's home directory is owned by foo:foo, not foo:users.

For this to work, I need to set the umask to 002 globally.

After a quick grep -RIi umask /etc/*, it seemed for a moment that modifying the UMASK entry in /etc/login.defs should do the trick. It does, too -- but only for console logins.

If I log in to my desktop, and open a terminal there, I still get to see the default umask 022. Same goes for files created from apps started through the menu. Apparently, the display manager (or whatever X11 component responsible) does source some different setting than a console login does, and damned if I could tell which one it is. (I tried changing the setting in /etc/init.d/rc, and no, it did not help.)

How / where do I set umask globally (and for all users), so that the X11 desktop environment gets the memo as well?

(The system is Linux Mint / Ubuntu, in case that changes anything...)