$ sudo apt install devops-knowledge

Linux for DevOps
Instructor Guide

Step-by-step explanations with real terminal examples for every module

01
Introduction to Linux & Why It Matters in DevOps
Setting the stage — what Linux is and where students will encounter it
▾

How to explain to students

Start by asking: "When you visit Netflix, GitHub, or Google — what OS do you think is running those servers?" The answer is almost always Linux. Explain that over 96% of web servers run Linux. DevOps is about automating those servers, so Linux is non-negotiable.

Use the analogy: "Windows is like an automatic car. Linux is a manual — harder to learn, but gives you full control over every gear."

bash — why-linux.sh
# Where will students use Linux in DevOps?
# ✅ Docker containers → run on Linux
# ✅ AWS/GCP/Azure VMs → Linux by default
# ✅ CI/CD pipelines (GitHub Actions, Jenkins)
# ✅ Kubernetes nodes → Linux

$ uname -a
Linux devbox 5.15.0 #1 SMP x86_64 GNU/Linux

# This single line tells you kernel, hostname, architecture
🐧
Free & Open Source
No licensing costs. Companies save millions deploying Linux at scale.
⚡
Lightweight
Can run on minimal hardware — perfect for containers and cloud VMs.
🔧
Customizable
Every part of the OS can be tweaked, scripted, or automated.
🔒
Secure by design
Permissions, users, and groups are first-class citizens.
02
Terminal Navigation & File Management
Moving around the filesystem and managing files from the command line
▾

How to explain to students

Compare the terminal to a GPS for your computer. pwd is "where am I?", ls is "what's around me?", and cd is "go there". Give students a real folder structure to navigate.

Live demo: Create a fake project structure on screen and let students replicate it. Nothing teaches mkdir and cp faster than actually using them.

bash — navigation demo
$ pwd  # Print current directory
/home/student

$ ls -la  # List all files with details
drwxr-xr-x 3 student student 4096 Apr 25 10:00 projects
-rw-r--r-- 1 student student 220 Apr 25 09:00 .bashrc

$ mkdir -p projects/webapp/config
$ cd projects/webapp
~/projects/webapp $ touch index.html app.js

$ cp index.html index.html.bak  # Backup before editing!
$ mv index.html.bak archive/
$ rm -rf archive/  # ⚠️ No recycle bin!
pwd ls -la cd .. mkdir -p cp / mv / rm ⚠️ rm -rf is permanent
03
File Permissions, Users, Groups & SSH Keys
Linux security model — who can read, write, and execute what
▾

How to explain permissions

Use the apartment analogy: A file is an apartment. The owner has a key. The group is like the floor — neighbors with shared access. Others are strangers. Permissions (rwx) decide what each can do.

Teach chmod with the numeric system. It clicks instantly once students see 7 = 4+2+1 = read+write+execute.

bash — permissions
# Read a permission string: -rwxr-xr--
# Position: [type][owner][group][others]
# r=4, w=2, x=1 → 7=rwx, 5=r-x, 4=r--

$ ls -l script.sh
-rw-r--r-- 1 student devs 512 Apr 25 script.sh

$ chmod 755 script.sh  # owner=rwx, group=r-x, others=r-x
$ ls -l script.sh
-rwxr-xr-x 1 student devs 512 Apr 25 script.sh

# SSH Key Setup
$ ssh-keygen -t ed25519 -C "student@devops"
Generating public/private ed25519 key pair.
Enter file: ~/.ssh/id_ed25519

$ ssh-copy-id student@server.example.com
Number of key(s) added: 1 ✓

# Now login without password:
$ ssh student@server.example.com
🔑
chmod 600 private keys
SSH private keys must be readable only by owner. SSH will refuse to work otherwise.
👥
useradd / usermod
Create users and add them to groups like sudo or docker.
🛡️
sudo vs su
sudo = one command as root. su = switch user entirely. Prefer sudo.
04
Package Management & System Updates
apt (Ubuntu/Debian) and yum/dnf (RHEL/CentOS) — installing and updating software
▾

How to explain to students

Compare apt to the App Store — but for the terminal, and way faster. Ask students: "Imagine installing Photoshop just by typing one command." That's what package managers do.

Emphasize that in DevOps, servers must be kept updated for security. Outdated packages are a top cause of breaches. apt upgrade is like pressing "Update All" on your phone.

bash — package management
# === Ubuntu / Debian (apt) ===
$ sudo apt update  # Refresh package list
$ sudo apt upgrade -y  # Upgrade all packages
$ sudo apt install nginx git curl -y
$ sudo apt remove nginx
$ apt search python3  # Find packages

# === RHEL / CentOS (yum/dnf) ===
$ sudo yum update -y
$ sudo dnf install nginx -y  # dnf = modern yum

# Check if a service is running after install
$ sudo systemctl status nginx
● nginx.service - A high performance web server
Active: active (running) since Fri 2025-04-25
apt update apt upgrade apt install yum / dnf systemctl
05
Writing Bash Scripts for Automation
From one-liners to full automation scripts with variables, loops, and conditionals
▾

How to explain to students

Tell students: "Every time you do something more than twice in the terminal, write a script." Scripts are just saved commands. Start with a simple "Hello, World" script, then build up to variables, if-else, and loops.

The shebang line #!/bin/bash is magic — explain it tells the OS which interpreter to use. Without it, the script might not run.

bash — first_script.sh
#!/bin/bash  # Always start with this!

# Variables
NAME="DevOps Student"
DATE=$(date +%Y-%m-%d)  # Command substitution
echo "Hello $NAME — today is $DATE"

# If-else
DISK=$(df / | awk 'NR==2{print $5}' | tr -d '%')
if [ "$DISK" -gt 80 ]; then
  echo "⚠️ Disk usage is ${DISK}% — WARNING!"
else
  echo "✅ Disk usage is ${DISK}% — All good"
fi

# Loop through files
for FILE in /var/log/*.log; do
  echo "Found log: $FILE"
done
📝
Always use quotes
Use "$VAR" not $VAR to avoid word-splitting bugs with spaces.
🧪
Test with set -x
Add set -x at the top to print each command as it runs — great for debugging.
🚨
Exit on error
Add set -e to stop the script immediately if any command fails.
06
Using AI to Write & Debug Bash Scripts
Leveraging AI tools as a DevOps pair programmer
▾

How to explain to students

Teach students that AI is a force multiplier, not a replacement. The goal is to know enough Linux to verify and modify what AI generates. Bad prompt = bad script. Good prompt = great starting point.

Show a before/after: a vague prompt gives a generic script, a detailed prompt gives a production-ready one. Teach students to always read, test, and understand AI output before running it on a server.

bash — AI prompting examples
# ❌ Weak prompt → weak script
"Write a bash script to monitor disk"

# ✅ Strong prompt → production-ready script
"Write a bash script that:
- Checks disk usage on / every 5 minutes
- Alerts if usage exceeds 85%
- Logs to /var/log/disk-monitor.log with timestamps
- Sends email using sendmail if available
- Handles errors and uses set -e, set -u"

# Debug tip: Paste error into AI with context
./monitor.sh: line 12: [: too many arguments
# Ask: "What does this bash error mean and how do I fix it?"
ChatGPT Claude GitHub Copilot Always review AI output Understand before running
07
Project: Disk Usage Monitor with Alerts
Real-world bash script that monitors disk, logs results, and sends alerts
▾

How to explain to students

This is where everything comes together. Walk through the script line by line before asking students to build it. Emphasize: this is the kind of script that runs on real production servers at companies like Amazon and Netflix.

bash — disk_monitor.sh (complete project)
#!/bin/bash
set -euo pipefail  # Strict mode

# ── Configuration ──────────────────────
THRESHOLD=85
LOG_FILE="/var/log/disk_monitor.log"
ALERT_EMAIL="admin@company.com"
TIMESTAMP=$(date '+%Y-%m-%d %H:%M:%S')

# ── Functions ───────────────────────────
log() { echo "[$TIMESTAMP] $*" | tee -a "$LOG_FILE"; }

check_disk() {
  local USAGE
  USAGE=$(df / | awk 'NR==2 {print $5}' | tr -d '%')
  log "Disk usage: ${USAGE}%"

  if [[ "$USAGE" -ge "$THRESHOLD" ]]; then
    log "🚨 ALERT: Disk at ${USAGE}% — threshold is ${THRESHOLD}%"
    echo "Disk alert on $(hostname)" | mail -s "Disk Alert" "$ALERT_EMAIL" 2>/dev/null || true
  else
    log "✅ OK — ${USAGE}% used"
  fi
}

# ── Main ────────────────────────────────
log "=== Disk Monitor Started ==="
check_disk

# Schedule with cron: */5 * * * * /usr/local/bin/disk_monitor.sh
📅
Add to cron
Run crontab -e and schedule this script every 5 minutes automatically.
📂
Log rotation
Mention logrotate — logs need to be rotated or they fill the disk you're monitoring!
🧩
Extend it
Challenge: add monitoring for CPU, memory, or check multiple mount points.
08
Quiz: Linux Commands & Permissions
10 MCQs + 2 fill-in-the-command questions
▾

Sample quiz questions (interactive)

Q1. Which command shows the current working directory?
A
ls
B
cd
C
pwd
D
echo
Q2. What does chmod 644 file.txt mean?
A
Everyone can read and write
B
Owner: rw-, Group: r--, Others: r--
C
Owner: rwx, Group: r-x, Others: r--
D
Read-only for everyone
Q3. Which command installs a package on Ubuntu?
A
yum install nginx
B
brew install nginx
C
sudo apt install nginx
D
sudo get nginx
Q4. What does set -e do in a bash script?
A
Exit immediately if any command fails
B
Enable debugging output
C
Set an environment variable
D
Suppress all errors
Q5. Which SSH key type is recommended for new setups?
A
RSA 1024-bit
B
DSA
C
ed25519
D
ECDSA 256-bit

Fill-in-the-command

Fill 1: What command makes script.sh executable by the owner only?
Fill 2: Write the cron expression to run a script every day at 2:30 AM.
09
Assignment: Backup Script with Logging
Write a bash script that backs up a folder and logs all results
▾

How to explain to students

Frame this as a real job task: "Your manager asks you to set up an automated nightly backup for the /var/www/html folder. It must log success or failure. You have 24 hours." This mirrors what junior DevOps engineers actually do in their first week.

📋 Assignment Requirements

  • Accept a source folder as a script argument (e.g., ./backup.sh /var/www/html)
  • Create a timestamped .tar.gz backup in /backups/ directory
  • Log success or failure with timestamps to /var/log/backup.log
  • Handle edge cases: source not found, backup dir doesn't exist, disk full
  • Use functions, variables, and proper error handling (set -e)
  • Bonus: Delete backups older than 7 days automatically
  • Bonus: Send an email alert on failure
bash — expected output when grading
$ ./backup.sh /var/www/html
[2025-04-25 02:30:01] Backup started for: /var/www/html
[2025-04-25 02:30:03] ✅ Backup created: /backups/html_2025-04-25_02-30-01.tar.gz
[2025-04-25 02:30:03] Size: 24M
[2025-04-25 02:30:03] Cleaning up backups older than 7 days...
[2025-04-25 02:30:03] ✅ Backup completed successfully

$ cat /var/log/backup.log
[2025-04-25 02:30:01] Backup started for: /var/www/html
[2025-04-25 02:30:03] ✅ Backup created: html_2025-04-25_02-30-01.tar.gz
📊
Grading rubric
Script runs: 30pts. Logging works: 25pts. Error handling: 25pts. Code quality: 20pts.
🎯
Common mistakes
Hardcoded paths, no quotes around variables, missing shebang, no error checking.
💡
Extend challenge
Add the cron job that runs this script automatically at 2 AM every night.