ps and kill: Manage Processes in Linux

Quick take: Use ps aux to list running processes and find a PID, then kill PID to stop one gracefully or kill -9 PID to force it. Use pkill name or killall name to stop processes by name.

Introduction

Managing processes is core to Linux administration, and two commands handle most of it: ps lists what is running, and kill sends signals to stop it. Around them sit helpers like pgrep, pkill, and killall for working with processes by name.

This guide covers listing and finding processes, the signals kill can send, and the safe way to terminate a misbehaving process.

Syntax

The basic syntax of the ps and kill command is:

ps [OPTIONS]
kill [-SIGNAL] PID

Common Options and Parameters

The most useful options and parameters for the ps and kill command:

Practical Examples

Real ps and kill commands you can run today:

# List all processes
ps aux
# Find a specific process and its PID
ps aux | grep nginx
# Stop a process gracefully by PID
kill 4821
# Force-kill an unresponsive process
kill -9 4821
# Stop every matching process by name
pkill firefox
# Find PIDs by name
pgrep -l sshd
# Reload a service by sending HUP
sudo kill -1 $(pgrep nginx | head -1)

Understanding Linux Signals

kill does not only “kill” — it sends a signal, and choosing the right one matters. The common ones are:

Always try SIGTERM first so the process can flush data and close files cleanly. Reserve SIGKILL for processes that ignore TERM — pulling the plug with -9 can leave temporary files or locks behind.

Finding and Stopping Runaway Processes

When a server is overloaded, the goal is to find the offending process quickly and stop it without harming others. Combine ps with sorting, or jump straight to the live monitors.

# Top 5 CPU consumers
ps aux --sort=-%cpu | head -6

# Top 5 memory consumers
ps aux --sort=-%mem | head -6

# Stop every worker of a runaway app by name
pkill -f 'python worker.py'

The -f flag to pkill matches against the full command line, which is essential when many processes share the same executable name but differ in their arguments.

Tips and Best Practices

• Always try a plain kill (TERM) first — it lets the process clean up. Reserve kill -9 (KILL) for processes that ignore it.
• Use pgrep/pkill instead of parsing ps | grep by hand — they are safer and avoid matching the grep process itself.
• ps aux --sort=-%mem | head quickly shows the biggest memory consumers.

Final Thoughts

ps and kill are the foundation of process control in Linux: list with ps aux, find the PID, then signal it with kill. Prefer a graceful TERM before a forceful -9, and use pgrep and pkill to work by name. For a live, interactive view of processes, move on to top and htop.