htop and glances interactive process viewers for Linux Servers.

This is htop, an interactive process viewer for Unix systems. It is a text-mode application (for console or X terminals) and requires ncurses.
I am using this brilliant app for monitoring my servers and Raspberry Pi. Download

I recommend use PyPi:

Glances – “An Eye on your system”
Glances is a cross-platform system monitoring tool. Written in Python, Glances will run on almost any platform : GNU/Linux, FreeBSD, OS X and Windows.

You can enable many useful plugins using the following command.

or with python3

Configuration file options:

Ncdu is also a brilliant command line disk usage analyzer with an ncurses interface.