Read system load at a glance.

htop

Read load against core count

Load above the core count means runnable work is queueing. The number alone does not say the machine is slow.

Sort by memory and then by CPU

Press F6 repeatedly to change the sort column, or F7 to cycle trees.

Show only a subtree

htop -u www-data

One-shot snapshot for a script

top -bn1 -o %CPU | head -12

Scope: htop