On Linux and Mac systems, the top terminal command gives you a great bird's eye view of what your system is doing. A few helpful keyboard shortcuts make top an even more useful system command tool.
Simply entering top into a terminal gives you a list of processes running on your system, their process ID (PID), and useful information on those processes, like how many CPU and memory resources they're using. Want to kill a runaway app that's eating up your CPU cycles? With top running, you can do it right there:
Once you've located a process that needs to be killed, press ‘k' which will ask for the process id, and signal to send. If you have the privilege to kill that particular PID, it will get killed successfully.
Hit the link for more tips on top. If you're a frequent terminal user yourself, tell us how you make use of the uber-helpful command in the comments.
Can You Top This? 15 Practical Linux Top Command Examples [The Geek Stuff via Every Joe]