Find and Kill a Process in Linux — ps, kill, pkill

To end a process in Linux, first find its PID (identifier) with ps or pgrep, then send it a signal with kill. To finish a process by name, pkill and killall are handy. Let’s take it step by step.

Step 1. Find the process

Show all processes and filter by name with grep:

ps aux | grep nginx

In the output the second column is the PID. A more direct way is pgrep, which returns the identifiers straight away:

pgrep -a nginx

The -a flag shows the PID together with the command line.

If the process is holding a network port, find it by that port:

sudo ss -ltnp | grep :80

Step 2. End the process by PID

The standard command is kill. By default it sends the TERM signal (15) — a polite request to shut down that lets the process save its data:

kill 12345

If the process does not react, send the KILL signal (9) — a forced termination with no chance to save anything:

kill -9 12345

Always try a plain kill first, and only use -9 if the process is stuck.

Ending a process by name: pkill and killall

You do not have to look up the PID — you can end a process by name.

pkill matches part of the name:

pkill nginx
pkill -9 nginx

killall ends every process with an exact name:

killall nginx

Be careful: pkill php ends every process whose name contains php.

Killing from htop

The visual way is through htop:

htop

Find the process (press F3 to search), select it with the arrow keys and press F9. Choose the signal (usually SIGTERM, then SIGKILL) and confirm.

The main signals

Reloading a service configuration without stopping it is often done like this:

kill -HUP 12345

Finding the process that loads the system

To find the hungriest process by CPU:

ps aux --sort=-%cpu | head

By memory:

ps aux --sort=-%mem | head

Frequently asked questions

How does kill -15 differ from kill -9? -15 (TERM) asks the process to shut down properly: close files, save data. -9 (KILL) kills it instantly and it saves nothing. Start with -15.

The process will not die even with -9. What now? That happens with processes in state D (uninterruptible sleep, usually waiting on disk). They cannot be killed until the I/O operation finishes; sometimes only a reboot helps.

How do I end a process when I only know the port? Find the PID with sudo ss -ltnp | grep :PORT, then run kill PID. Or do it in one command: sudo fuser -k 80/tcp.

Is killall dangerous? It ends every process with the given name. Check the list first with pgrep -a name so you do not stop more than you meant to.

Summary

ps/pgrep for finding and kill/pkill for ending cover almost every process management task. The rule is simple: a gentle TERM first, and KILL only for the ones that hang.

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