Linux/Unix: Process & Job Control – ps, jobs, kill, nice, and More

Introduction – Take Control of Processes in Linux/Unix

In Linux/Unix, process management is a vital skill for every system user and administrator. From monitoring system performance to handling background jobs and adjusting task priorities, understanding how to control processes gives you command over your system.

In this guide, you’ll learn:

• How to view running processes with ps, top, and htop
• How to manage foreground and background jobs
• How to kill or signal processes safely
• How to schedule and prioritize processes using nice and renice

Topics Covered

Linux/Unix: Process Overview & Commands (ps, pstree, top, htop)

ps – Snapshot of Active Processes

ps aux

Shows all processes with user, PID, CPU%, memory usage, and command.

top – Real-Time Monitoring

top

Live view of processes and system performance. Press q to quit.

htop – Interactive Alternative to top

htop

Scrollable interface, tree view, kill processes with a keypress.

pstree – Process Tree View

pstree

Displays hierarchical relationship between processes.

Linux/Unix: Background & Foreground (jobs, bg, fg, disown)

Send Job to Background

sleep 100 &

Appends & to run the command in the background.

List Background Jobs

jobs

Resume Job in Background/Foreground

bg %1     # Resume job 1 in background
fg %1     # Bring job 1 to foreground

Disown a Job (Detach from Shell)

disown %1

Removes job from job table to avoid termination on shell exit.

Linux/Unix: Killing & Signaling (kill, killall, pkill, xkill)

kill – Send Signal to PID

kill -9 1234

Sends SIGKILL to process with PID 1234.

killall – Kill by Name

killall firefox

pkill – Pattern-Based Process Kill

pkill -f "python script.py"

xkill – Click-to-Kill GUI App (X11 Only)

xkill

Linux/Unix: Scheduling (nice, renice, chrt)

nice – Launch Process with Priority

nice -n 10 myscript.sh

Starts with niceness of 10 (lower priority). Default is 0.

renice – Adjust Priority of Running Process

renice +5 -p 1234

Increases niceness (decreases priority) for process 1234.

chrt – Set Real-Time Scheduling Policies

chrt -f -p 99 1234

Applies FIFO scheduling policy to PID 1234 with highest priority (99).

Summary – Recap & Next Steps

Linux provides robust tools to monitor, manage, and control processes and jobs. From checking what’s running to adjusting how and when it runs, these tools are essential for resource control, automation, and stability.

Key Takeaways:

• Use ps, top, and htop to view and manage running processes.
• Move jobs between foreground/background with bg, fg, jobs, and disown.
• Terminate or signal processes with kill, killall, and pkill.
• Adjust CPU priority using nice, renice, or real-time policies with chrt.

Practical Use Cases:

• Free system memory by killing zombie or rogue processes.
• Manage long-running background jobs or scheduled scripts.
• Improve system performance by reprioritizing tasks during heavy load.

Frequently Asked Questions

What’s the difference between kill and killall?
kill targets a specific PID, while killall targets all processes with the given name.

How can I safely close a process without using -9?
Use kill -15 PID (SIGTERM) to allow cleanup before forced termination.

What does nice and renice do?
These control CPU scheduling priority. Lower nice = higher priority.

Can I see all jobs running in the background?
Yes. Run jobs to list background jobs in the current shell.