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As it comes from htop’s manual page, htop is free (GPL) ncurses-based process viewer, that is similar to top, but allows to scroll the list vertically and horizontally to see all processes and their full command lines. Tasks related to processes (killing, renicing) can be done without entering their PIDs.

I found this utility very useful and powerful in my everyday working process. Here is the comparison between htop and oldie top (taken from htop’s site):
In ‘htop’ you can scroll the list vertically and horizontally to see all processes and complete command lines.- In ‘top’ you are subject to a delay for each unassigned key you press (especially annoying when multi-key escape sequences are triggered by accident).
- ‘htop’ starts faster (’top’ seems to collect data for a while before displaying anything).
- In ‘htop’ you don’t need to type the process number to kill a process, in ‘top’ you do.
- In ‘htop’ you don’t need to type the process number or the priority value to renice a process, in ‘top’ you do.
- ‘htop’ supports mouse operation, ‘top’ doesn’t
- ‘top’ is older, hence, more used and tested.
As usual it’s possible to install htop in Ubuntu by single command: sudo aptitude install htop.

Check here how to install in other Distros.
http://www.go2linux.org/htop-linux-command-line-to-monitor-linux-systems
htop is really cpu consuming. i started using it on monitoring in fast way my machines but i came up as cpu consuming so i use top. top is cpu consuming too but not that much. i wait for improovements in htop. there will be. but if you don’t care about cpu usage, its a must