Lesson 14: Process Management

Goal: Learn to monitor, control, and manage running processes and system resources.

Table of Contents

1. List Processes — ps
2. Live Monitor — top
3. Interactive Monitor — htop & btop
4. Kill Processes — kill & signals
5. Background & Foreground Jobs
6. Measure Execution Time — time
7. Exercises

List Processes — ps

Show your processes

ps

Show ALL processes (most common)

ps aux

Output:

USER       PID %CPU %MEM    VSZ   RSS TTY      STAT START   TIME COMMAND
root         1  0.0  0.1 169936 13212 ?        Ss   Feb05   0:12 /sbin/init
benjamin  1234  0.5  1.2 456780 98304 ?        Sl   10:00   0:45 /usr/bin/code

Process states (STAT)

Filter processes

# Find a specific process
ps aux | grep nginx

# Exclude the grep itself
ps aux | grep [n]ginx

# Show process tree
ps auxf

# Show processes for a specific user
ps -u benjamin

# Show by PID
ps -p 1234

# Custom output format
ps -eo pid,user,%cpu,%mem,comm --sort=-%cpu | head -20

pgrep — find PIDs by name

pgrep nginx
pgrep -l nginx        # with process name
pgrep -a nginx        # with full command
pgrep -u benjamin     # by user

Live Monitor — top

top

top interface

top - 14:30:00 up 45 days,  3:22,  2 users,  load average: 0.12, 0.08, 0.05
Tasks: 245 total,   1 running, 244 sleeping,   0 stopped,   0 zombie
%Cpu(s):  2.5 us,  1.0 sy,  0.0 ni, 96.0 id,  0.5 wa,  0.0 hi,  0.0 si
MiB Mem:  16384.0 total,   8192.0 free,   4096.0 used,   4096.0 buff/cache
MiB Swap:  4096.0 total,   4096.0 free,      0.0 used.  11264.0 avail Mem

  PID USER      PR  NI    VIRT    RES    SHR S  %CPU  %MEM   TIME+ COMMAND
 1234 benjamin  20   0  456780  98304  45678 S   5.0   0.6   0:45 code

top keyboard shortcuts

Interactive Monitor — htop & btop

htop

sudo apt install htop
htop

htop is a much better version of top with:

• Color-coded output
• Mouse support
• Visual CPU/memory bars
• Easy process killing with F9
• Tree view with F5

htop keyboard shortcuts

btop

sudo apt install btop
btop

btop is even more advanced with GPU monitoring, network graphs, and a modern interface.

Kill Processes — kill & signals

Basic kill

# Graceful shutdown (SIGTERM = 15)
kill 1234

# Force kill (SIGKILL = 9)
kill -9 1234

# Kill by name
killall nginx

# Kill by name (more flexible)
pkill nginx

# Kill by partial name match
pkill -f "python script.py"

Common signals

List all signals

kill -l

Practical examples

# Reload nginx configuration without stopping
sudo kill -HUP $(pgrep nginx | head -1)

# Pause a process
kill -STOP 1234

# Resume a paused process
kill -CONT 1234

# Kill all processes of a user
sudo pkill -u baduser

# Kill all processes matching a pattern
pkill -f "npm start"

Always try SIGTERM first

# Step 1: Ask nicely
kill 1234

# Step 2: Wait a few seconds, check if it's gone
sleep 3 && ps -p 1234

# Step 3: Only if still running, force it
kill -9 1234

Background & Foreground Jobs

Run a command in the background

# Append & to run in background
sleep 100 &
# Output: [1] 5678 (job number and PID)

List background jobs

jobs
# Output: [1]+  Running  sleep 100 &

Manage jobs

# Bring job to foreground
fg %1

# Send running job to background
# 1. Press Ctrl+Z (pause it)
# 2. Then:
bg %1

# Disown a job (won't be killed when terminal closes)
disown %1

nohup — Survive logout

# Run a command that survives logout
nohup ./long-script.sh &

# Output goes to nohup.out by default
# Redirect output
nohup ./script.sh > output.log 2>&1 &

Practical workflow

# 1. Start a long download
wget https://example.com/large-file.iso &

# 2. Check it's running
jobs

# 3. Do other work...

# 4. Bring it back to foreground if needed
fg %1

Measure Execution Time — time

time measures how long a command takes to run.

time ls -la /etc

Output:

real    0m0.012s    ← Wall clock time
user    0m0.004s    ← CPU time in user mode
sys     0m0.008s    ← CPU time in kernel mode

Practical examples

# Time a script
time ./deploy.sh

# Time a build
time npm run build

# Time a database query
time psql -c "SELECT COUNT(*) FROM users;" mydb

# Compare two approaches
time find / -name "*.log" 2>/dev/null
time locate "*.log"

Exercises

Exercise 1: Process inspection

# 1. Show all running processes
ps aux | head -20

# 2. Find the most CPU-intensive processes
ps aux --sort=-%cpu | head -10

# 3. Find the most memory-intensive processes
ps aux --sort=-%mem | head -10

# 4. Show processes as a tree
ps auxf | head -30

# 5. Count total running processes
ps aux | wc -l

Exercise 2: Background jobs

# 1. Start a background process
sleep 60 &

# 2. Check it's running
jobs

# 3. Bring it to foreground
fg %1

# 4. Pause it (Ctrl+Z)
# Press Ctrl+Z

# 5. Resume in background
bg %1

# 6. Kill it
kill %1

Exercise 3: Signals

# 1. Start a process
sleep 300 &
echo "PID: $!"

# 2. Check it's running
ps -p $!

# 3. Send SIGTERM
kill $!

# 4. Verify it's gone
ps -p $! 2>/dev/null || echo "Process terminated"

Key Takeaways

• ps aux — snapshot of all processes
• top — live process monitor (basic)
• htop / btop — interactive process monitor (recommended)
• kill PID — graceful stop; kill -9 PID — force stop
• killall name / pkill pattern — kill by name
• command & — run in background
• fg / bg — foreground/background control
• nohup — survive terminal close
• time command — measure execution time

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