Our lab linux machines use an inhouse setup to do screen locking and auto-logout. If you want a screen saver mode other than random here is what you do:

1. Look at the manual page for xlock and pick a mode you like.
2. Create a file in your home directory called .lockmode containing the name of the mode you want.

For example, if I wanted the mode called “space” which gives a moving star field I could get it by typing the following in a terminal:

cat > ~/.lockmode
space

Cntrl+D