⚙️ 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, andhtop - How to manage foreground and background jobs
- How to kill or signal processes safely
- How to schedule and prioritize processes using
niceandrenice
📘 Topics Covered
| 🔵 Subtopic | 📖 Description |
|---|---|
Process Overview (ps, top, htop) | View running processes, IDs, memory, and CPU usage |
Background & Foreground (jobs, bg, fg) | Manage jobs suspended or running in the background |
Killing & Signaling (kill, killall, pkill) | Terminate processes or send specific signals |
Scheduling & Priority (nice, renice, chrt) | Adjust CPU priority and scheduling class of processes |
🔵 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, andhtopto view and manage running processes. - Move jobs between foreground/background with
bg,fg,jobs, anddisown. - Terminate or signal processes with
kill,killall, andpkill. - Adjust CPU priority using
nice,renice, or real-time policies withchrt.
⚙️ 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.
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