I've just given up hope of getting gnome-screensaver to work for me, so now I've having a go with xscreensaver instead. I've followed procedure recommended as in http://www.liberiangeek.net/2011/10/...neiric-ocelot/

... having done ...
1. Removed the gnome-screensaver one
2. Done sudo apt-get install xscreensaver xscreensaver-gl-extra xscreensaver-data-extra
3. Added xscreensaver -nosplash to my Startup Applications (and re-booted)
4. Found xscreensaver-demo screen (not in Dash as recommended, since I'm on Classic Gnome, but it's just the same screen as in the Liberian Geek howto article)
5. Set all my options to 1 minute
6. (including successfully previewing my chosen screensaver)
7. Waited a minute -- and waited...

8. Also tried invoking the screen lock, both from the login/shutdown options at the top right of my screen, and by Ctrl-Alt-L. That doesn't work either. The only thing that *does* work is if I open Terminal and invoke xscreensaver -lock.

9. Started to wonder if I'm being really stupid!

Grateful in advance!
Piers.

Well, aren't computers wonderful!

During the course of today, (yesterday actually, now it's past midnight,) I've had occasion to re-boot quite a few times, and the xscreensaver has never worked. Now it's suddenly sprung to life. So that part of my problem is now [SOLVED].

But I'm still not getting any joy on screen-locking.

xscreensaver-command -lock invoked from Terminal works as intended

when screensaver cuts in, screen is not locked as intended, but "goes live" again without requiring a password

"lock screen" option from login/shutdown menu at top right has no effect whatsoever, although it intermittently (i.e. *sometimes* only) reports that gnome-screensaver (which I uninstalled earlier) can't be found. Why is it looking for the gnome version rather than the x version, I wonder?

Ctrl-Alt-L has no effect whatsoever

I'm getting different results at different times of day, and now feeling confused!

Xscreensaver-demo has a checkbox on the "Display Modes" tab to enable locking the screen. Try running xscreensaver-demo and using that.

Thanks frankbell -- yes, I already ticked that checkbox... something else is wrong...