As you may know, Gnome comes preinstalled with a few catalog of basic screensavers: Gnome Screensaver which is the default screen saver and locker in a Gnome desktop. It is designed with simplicity and security in mind.

For this reason many useres prefer to use xscreensaver wich is a better, more secure and universally accepted screensaver program for Unix-like operating systems.

In fact xscreensaver can be found installed by default on some Linux distributions like Ubuntu and latest versions of SUSE, but there are still Red Hat based systems that do not install this packages.

To install xscreensaver you can use the standard repositories from your specific OS.

Red Hat based:
su -c "yum install xscreensaver"

Debian based:
sudo apt-get install xscreensaver

Now xscreensaver is installed, we launch the configuration screen by typing xsreensaver-demo on a console or by clicking on System > Preferences > Look and Feel > Screensaver. This will pop a message asking you to deactivate the gnome-screensaver daemon which should be fine.

Select the screensaver design of your choice, hit the Preview button and close the dialog box when you’re done.

At this point, the screensaver should lock automatically after the defined inactive time, BUT it wont work if you want to activate it manally by pressing Ctrl+Alt+L or System > Lock Screen. This is because even when you defined xscreensaver as the default application, gnome is still looking for the old daemon in order to activate the screensaver.

To solve this problem open a terminal as root and issue the following command:

ln -sf /usr/bin/xscreensaver-command \
/usr/bin/gnome-screensaver-command

Now you can lock your screen and start xscreensaver with the standard gnome commands.