Conky is a light-weight and highly configurable system monitor for X. It can monitor many different aspects of your Linux computer. You choose what to monitor and you choose where the monitor is displayed on your desktop through use of a configuration file
.conkyrc. As for me I like to have it at the top right of my display.
To get conky running in Ubuntu execute:
sudo apt-get install conky
sudo yum install conky
Then regardless distro you use, you should edit configuration file that is located at your home directory ~/.conkyrc. For example like this one.