Add a screensaver to Ubuntu 12.04.

Ubuntu 12.04 does not ship with any screen savers, just a black screen that appears when your system is idle. If you would like to have a screensaver, please follow the steps below:

Uninstall a gnome-screensaver.
sudo apt-get purge gnome-screensaver

Install XScreenSaver.
sudo apt-get install xscreensaver xscreensaver-gl-extra xscreensaver-data-extra

Create a symbolic link for Ctrl+Alt+L is the default shortcut that locks your computer.
sudo ln -s /usr/bin/xscreensaver-command /usr/bin/gnome-screensaver-command

Finally, add the xscreensaver -nosplash to the Startup Applications.

Create the /dev/random

In SUSE Linux Enterprise Server 10 the /dev/random is missing, to create it use the mknod command (mknod – make block or character special files):

mknod /dev/random c 1 9

The /dev/random is a special file that serves as a random number generator or as a pseudorandom number generator. It allows access to environmental noise collected from device drivers and other sources.[citation needed] Not all operating systems implement the same semantics for /dev/random. Linux was the first operating system to implement a true random number generator in this way.