Linux Process Management — ps, top, kill, htop Guide

Guide to managing Linux processes: ps, top, htop, kill, nice, nohup, jobs, and bg/fg. With practical examples. Free Linux sysadmin reference, no signup needed.

Listing Processes

ps aux

Show all processes (a=all users, u=user format, x=without tty)

ps aux | head -20

ps aux | grep nginx

Find specific process by name

ps -ef

Full-format listing (alternative to aux)

ps -ef | grep python

ps -ef --forest

Show process hierarchy (tree view)

ps -p 1234 -o pid,ppid,cmd,%cpu,%mem

Show specific process with custom columns

pgrep nginx

Find PIDs by name

pgrep -a nginx

pgrep -u www-data

Find PIDs owned by user

pgrep -u www-data -l

pstree

Display processes as a tree

pstree -p -u

pstree -p 1

Show tree rooted at PID 1 (systemd)

ls -la /proc/<pid>/

Inspect any process via /proc filesystem

cat /proc/1234/status

Real-time Monitoring

top

Classic real-time process monitor

top -u www-data

top -b -n 1

Batch mode — single snapshot to stdout

top -b -n 1 | head -20

htop

Interactive process viewer with colors and mouse support

htop -u deploy

Filter htop to specific user

glances

Cross-platform system monitor (install: pip install glances)

watch -n 2 'ps aux --sort=-%cpu | head -10'

Refresh top CPU processes every 2s

top Keyboard Shortcuts

kKill process by PID

rRenice (change priority)

PSort by CPU usage

MSort by memory usage

TSort by running time

uFilter by user

nChange number of processes shown

1Toggle per-CPU stats

hHelp screen

qQuit

fManage columns

WWrite current config to .toprc

htop Keyboard Shortcuts

F2 / SSetup (customize columns)

F3 / /Search process by name

F4Filter processes

F5 / tToggle tree view

F6Sort by column

F7 / ]Increase process priority (nice -)

F8 / [Decrease process priority (nice +)

F9 / kKill process (send signal)

SpaceTag/untag process

uFilter by user

IInvert sort order

qQuit

Killing Processes

kill <pid>

Send SIGTERM (15) to process — graceful stop

kill 1234

kill -9 <pid>

Send SIGKILL — force kill, no cleanup

kill -9 1234

kill -HUP <pid>

Send SIGHUP — reload config without restart

kill -HUP $(pgrep nginx)

kill -STOP <pid>

Pause/suspend process (SIGSTOP)

kill -STOP 1234

kill -CONT <pid>

Resume paused process (SIGCONT)

kill -CONT 1234

killall nginx

Kill all processes with that name (SIGTERM)

killall -9 nginx

Force kill all processes with name

pkill nginx

Kill by name pattern (more flexible than killall)

pkill -f 'python worker.py'

pkill -u deploy

Kill all processes owned by user

pkill -9 -u testuser

Signal Reference

Num

Name

Description

1SIGHUPHangup — reload config

2SIGINTInterrupt — same as Ctrl+C

3SIGQUITQuit — generates core dump

9SIGKILLKill — cannot be caught or ignored

15SIGTERMTerminate — graceful shutdown (default)

18SIGCONTContinue — resume suspended process

19SIGSTOPStop — suspend process (cannot ignore)

20SIGTSTPTerminal stop — Ctrl+Z

10SIGUSR1User-defined signal 1

12SIGUSR2User-defined signal 2

Process Priority (nice)

nice -n 10 ./backup.sh

Start process with lower priority (+10 nice)

nice -n -10 ./critical.sh

Start with higher priority (requires root)

sudo nice -n -10 ./critical.sh

renice 10 -p 1234

Change priority of running process

renice -5 -u deploy

Change priority of all processes by user

sudo renice -5 -u deploy

ps -l

Show NI (nice) value column for processes

ps -l | grep myapp

Background Jobs

command &

Run command in background

./server.sh &

nohup command &

Run immune to hangup — survives terminal close

nohup ./worker.sh >> /var/log/worker.log 2>&1 &

disown %1

Detach background job from shell (survives logout)

disown -h %1

jobs -l

List background jobs with PIDs

fg %1

Bring job 1 to foreground

bg %1

Send stopped job to background

Ctrl+Z

Suspend foreground process (send to stopped state)

Ctrl+C

Interrupt/kill foreground process

Open Files & Ports (lsof)

lsof -i :80

What process is listening on port 80

lsof -i :3000-4000

Processes on port range 3000–4000

lsof -i TCP --state LISTEN

All processes with open TCP listening sockets

lsof -p 1234

All files/sockets opened by PID 1234

lsof -u www-data

All files opened by user

lsof /var/log/nginx/access.log

Which process has this file open

ss -tulnp

Socket statistics — all TCP/UDP ports (faster than lsof)

ss -tnp | grep ESTABLISHED

Show established TCP connections

netstat -tulnp

Network connections (legacy, use ss)

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Frequently Asked Questions

How do I find and kill a process by name?

pkill nginx kills all processes named nginx. killall nginx does the same. Or find the PID with pgrep nginx then kill PID.

Is Linux Process Guide free?

Yes, Linux Process Guide on ToolPix is 100% free with no signup or installation required.

Is my data safe?

This is a static reference tool. No data is entered or transmitted.

How do I run a process in the background so it survives logout?

nohup command & — nohup ignores SIGHUP (logout signal) and & runs it in background. Or use screen/tmux to keep a persistent session.

What is the difference between kill -9 and kill -15?

kill -15 (SIGTERM) asks the process to terminate gracefully. kill -9 (SIGKILL) forces immediate termination — the process cannot catch or ignore it.

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