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Step 4 — Process Management (Ubuntu 24)

Type along exactly as shown. This step is written for absolute beginners and assumes no prior Linux experience.
Estimated time: ~10–15 minutes

What you’ll learn

What a process is and how to list them
How to watch the system in real time with top
How to start programs in the background and bring them to the foreground
How to stop/kill a process safely
How to view PIDs (Process IDs) and understand signals
(Optional) How to adjust priority with nice/renice

This expands the original brief step (ps/top/background jobs/kill) into a guided mini-lesson with checks, expected outputs, and troubleshooting.

Setup: Continue using your practice area from previous steps (recommended):
mkdir -p ~/playground && cd ~/playground

0) What’s a “process”?

A process is a running program (like the terminal, a text editor, a web browser tab, or a background task).
Linux gives every process a unique number called a PID (Process ID). You use the PID to control the process (e.g., to stop it).

1) List processes with `ps`

Show the first few running processes (system-wide view):

ps aux | head -n 15

a = show processes for all users
u = show the user/owner
x = include processes without a controlling terminal

More readable columns (top 10 by PID):

ps -o pid,ppid,user,%cpu,%mem,stat,cmd --sort=pid | head -n 10

pid = Process ID
ppid = Parent Process ID
%cpu, %mem = CPU and memory usage
stat = state (e.g., S sleeping, R running, T stopped)
cmd = the command used to start the process

2) Real-time view with `top`

Open an updating view of processes:

top

Keys you can try inside top:

P = sort by CPU
M = sort by memory
1 = show all CPU cores
q = quit

Optional: Install htop (sudo apt install -y htop) for a friendlier view. Launch with htop, quit with q.

3) Create a background process and manage jobs

Start a harmless background job:

sleep 300 &

sleep 300 waits for 300 seconds (5 minutes). The & runs it in the background so you get your prompt back.

List your jobs:

jobs

Bring the job to the foreground (if there’s one job, it’s usually %1):

fg %1

Now your terminal is “busy” waiting for sleep to finish. Press Ctrl + C to stop it.

Start it again in the background and suspend, resume flow:

sleep 300 &      # start in background
jobs             
fg %1            # bring to foreground
# Press Ctrl+Z   # suspend the foreground job
bg %1            # resume it in the background
jobs

Ctrl+Z = “pause” the foreground process.
bg = continue a paused job in the background.
fg = bring a background job to the foreground.

4) Find PIDs and kill a process safely

Create a background process to practice on:

sleep 400 &

Find its PID(s):

pgrep sleep

You’ll see one or more numbers (PIDs).

Ask a process to exit nicely (SIGTERM 15):

kill 15 <PID>

If it doesn’t exit after a few seconds, you can force it (SIGKILL 9):

kill -9 <PID>

Use -9 only if normal signals fail; it doesn’t let programs clean up.

Alternative: kill by name (use carefully):

pkill sleep        # stops all 'sleep' processes you own
# or
killall sleep

Confirm it’s gone:

pgrep sleep || echo "No sleep process found"

5) (Optional) Priority: nice and renice

Every process has a priority (niceness). Higher nice values (e.g., +10) = lower priority (more “polite”).
Lower nice values (e.g., -5) = higher priority (less “polite”). Negative values may require sudo.

Start a nice process:

nice -n 10 sleep 200 &

Check niceness (NI column):

ps -o pid,ni,cmd -p $(pgrep -n sleep)

Change niceness of a running process to be more polite (higher number):

renice +15 -p <PID>
ps -o pid,ni,cmd -p <PID>

To set a negative niceness (higher priority), you typically need sudo.

Stop leftover sleep processes:

pkill sleep

6) Practice tasks (do them now)

Start sleep 180 &. Then show your jobs, bring it to the foreground, suspend it, and resume it in the background.
Use pgrep sleep to find the PID and then terminate the process politely. Verify it’s gone.
Launch a “polite” (low-priority) task with nice and confirm the NI column shows the expected value.
Open top, press P to sort by CPU and M to sort by memory. Quit top.

Hints:

sleep 180 &; jobs; fg %1;  # then Ctrl+Z
bg %1; jobs
pgrep sleep; kill 15 <PID>; pgrep sleep || echo "done"
nice -n 10 sleep 120 &; ps -o pid,ni,cmd -p $(pgrep -n sleep)
top  # then P, M, q

Troubleshooting

Q: I lost my job number. How do I get the PID?
A: Use pgrep <name> (e.g., pgrep sleep). Then use kill with the PID.

Q: kill didn’t stop the process.
A: Try kill 15 <PID> again, wait a moment, then kill -9 <PID> as a last resort.

Q: I see “Operation not permitted” with renice.
A: Negative nice values (higher priority) generally require sudo. Increasing the niceness (e.g., +10, +15) is allowed.

Q: top won’t exit.
A: Press q to quit top.

Quick Quiz (1 minute)

What command shows an updating, real-time view of processes?
Which key in top sorts by CPU usage?
How do you start a command in the background?
How do you bring job %1 to the foreground?
What’s the difference between kill 15 <PID> and kill -9 <PID>?

Answers: top; P; add & at the end; fg %1; 15 asks nicely, -9 forces.

Next Step

Continue to Step 5 — Permissions & Ownership to learn how to read and change file permissions and ownership safely.

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