Hands-on Lab·Linux Foundation Certified System Administrator

Processes, signals and what is using the CPU

Finding the process, understanding what state it is in, and stopping it without breaking anything else. ps has two completely different option styles that produce the same processes, kill sends a signal rather than killing, and nice numbers run backwards from priority. All three cost marks.

Operations Deployment Guide 16 of 38 Intermediate

PlatformsUbuntu 26.04 LTS + AlmaLinux 10.2
LVM2.03.31 (Ubuntu) / 2.03.36 (AlmaLinux)
nftables1.1.6 (Ubuntu) / 1.1.5 (AlmaLinux)
TimeAbout 20 min

procps-ng on both families; ps, kill, nice and renice are identical. systemd-run needs systemd, which both have.

Firewallufw 0.36.2 enabled but reporting inactive / firewalld active
Network confignetplan + systemd-networkd / NetworkManager 1.56.0

Both families. The RHEL transcript came first, during an outage that took both Ubuntu hosts offline; the Ubuntu half was captured afterwards and is the last step of each page, because Ubuntu is what LFCS is most likely to sit you in front of.
Server Name	IP Address	OS	Roles	CPU	RAM	HDD
LFCS-A01	192.168.0.70	Ubuntu 26.04 LTS	Primary host - most guides run only here	2 Core	4 GB	50 GB
LFCS-C01	192.168.0.72	AlmaLinux 10.2	The other distribution - dnf, firewalld and NetworkManager	2 Core	4 GB	50 GB

This guide includes

Use this for finding and stopping the process you were asked about. This matters because niceness runs backwards from priority - and two signals cannot be caught at all.

using ps in both of its incompatible styles, and reading the state column as a diagnosis
reading the process tree, and finding the one you want four ways
asking what is using the CPU and the memory
sending signals, including the two that cannot be caught
setting niceness, which runs backwards, and starting a process that outlives your session

Before you start

guide 13 - services, whose processes these are.

ps, in its two incompatible styles
The state column, which is the diagnosis
The tree, and who started what
Finding the one you want
What is using the CPU and the memory
Signals, and the two that cannot be caught
Niceness runs backwards from priority
And a process that outlives your session
The same process tools on Ubuntu

Official sources

← All LFCS guides

Processes, signals and what is using the CPU

This guide includes

Before you start

ps, in its two incompatible styles

The state column, which is the diagnosis

The tree, and who started what

Finding the one you want

What is using the CPU and the memory

Signals, and the two that cannot be caught

Niceness runs backwards from priority

And a process that outlives your session

The same process tools on Ubuntu

Official sources