If you are new to Ubuntu or you recently upgraded your installation to 11.xx or higher you will notice that the system monitors you are familiar with are not compatible with new desktop. No worries though, there are a number of monitors available going by the name of “Indicators”, these tools will embed into your unity tool bar much the same way that your previous monitors had.
General System Monitor:
sudo apt-get install indicator-multiload
or from the ppa repository:
sudo add-apt-repository ppa:indicator-multiload/stable-daily sudo apt-get update sudo apt-get install indicator-multiload This indicator is a port of the original System Monitor GNOME Panel applet (gnome-system-monitor applet). and provides monitoring for the followingNetwork, memory and cpu usage.