Show the 20 most CPU/Memory hungry processes

Display the top 20 running processes - sorted by memory usage
ps returns all running processes which are then sorted by the 4th field in numerical order and the top 20 are sent to STDOUT.

ps aux | sort -nk +4 | tail -20

Show the 20 most CPU/Memory hungry processes
This command will show the 20 processes using the most CPU time (hungriest at the bottom).

ps aux | sort -nk +3 | tail -20

Or, run both:

echo "CPU:" && ps aux | sort -nk +3 | tail -20 && echo "Memory:" && ps aux | sort -nk +4 | tail -20