Linux Processes: ps, top and kill

Every running program is a process with its own number, called a PID. ps and top show what is running and how much it is using, and kill stops a process that is stuck.

Seeing what is running

ps aux

Lists every process, with its user, PID, CPU and memory use.

ps aux --sort=-%mem | head

Shows the processes using the most memory.

ps aux --sort=-%cpu | head

Shows the processes using the most CPU.

pgrep -a bash

Finds processes by name and shows their PIDs.

Watching live with top

top

Shows running processes, updating every few seconds. If it's installed, htop is easier to read and use.

Key	What it does
`P`	Sort by CPU use
`M`	Sort by memory use
`k`	Kill a process (asks for the PID)
`1`	Show each CPU core
`q`	Quit

Stopping a process

kill 1234

Asks process 1234 to close. Most programs tidy up and exit.

kill -9 1234

Forces process 1234 to stop immediately. Use this only if a normal kill doesn't work, as unsaved work is lost.

pkill firefox

Stops every process named firefox.

Be careful who you stop. Killing system processes can crash your computer. Check the name and PID with ps or pgrep first.

Quick reference

Option	Meaning
`ps aux`	List all processes
`pgrep -a name`	Find a process by name
`top / htop`	Watch processes live
`kill PID`	Ask a process to close
`kill -9 PID`	Force a process to stop
`pkill name`	Stop processes by name