Perhaps the most common way to monitor system resources in Ubuntu is to use System Monitor from the Administration menu. However, it would be much better if one can receive real time monitoring of system resources from the desktop.
System Load Indicator is a system tray version of System Monitor (Resources), which allows viewing CPU utilization, system load, hard disk, memory and network information from the system tray in custom colors. You can select specific colors for displaying every category and sub-category for monitoring a system resource. For example, you can select separate colors to view CPU usage by user and system processes. This can be quite useful for finding out the reasons for identifying resource hogging applications, by real time monitoring of resource utilization by applications.
After installation, you can launch System Load Indicator from Applications –> System Tools. Whereas, Unity Users can simply type the initials from Applications menu.
System Load Indicator, by default, only displays CPU usage when it is launched for the first time. To enable other features, click on real time monitoring graph from the system tray and choose Preferences.
From here, you can enable features such as the monitoring of memory, network, swap space, hard disk and processor.
Each category and sub-category can be defined custom colors to make the monitoring process easy to understand at a glance. For example, you can set different colors for memory utilization by user applications, buffers, as well as cached, available and shared memory. Similarly, separate colors can be set for monitoring other sub-categories of system resources. Once you have selected the system resources to monitor, a graph for each of them will instantly appear in the system tray. Providing you with real time monitoring of your system load.
System Load Indicator is available both in 32-bit and 64-bit versions. You can get the .deb package from the Launchpad link given below, for easy installation via the Ubuntu software center. It currently only works on the latest Ubuntu 11.04 version.