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Day 07 – Linux File System Hierarchy & Scenario-Based Practice

Task

Today's goal is to understand where things live in Linux and practice troubleshooting like a DevOps engineer.

You will create notes covering:

  • Linux File System Hierarchy (the most important directories)
  • Practice solving real-world scenarios step by step

This consolidates your Linux fundamentals and prepares you for real-world troubleshooting.

Expected Output

By the end of today, you should have:

  • A markdown file named: day-07-linux-fs-and-scenarios.md

or

  • A hand written set of notes (Recommended)

Your notes should have two sections: File System Hierarchy and Scenario Practice.

Guidelines

Part 1: Linux File System Hierarchy (30 minutes)

Document the purpose of these essential directories:

Core Directories (Must Know):

  • / (root) - The starting point of everything
  • /home - User home directories
  • /root - Root user's home directory
  • /etc - Configuration files
  • /var/log - Log files (very important for DevOps!)
  • /tmp - Temporary files

Additional Directories (Good to Know):

  • /bin - Essential command binaries
  • /usr/bin - User command binaries
  • /opt - Optional/third-party applications

For each directory:

  • Write 1-2 lines explaining what it contains
  • Run ls -l <directory> and note 1-2 files/folders you see
  • Write one sentence: "I would use this when..."

Hands-on task:

# Find the largest log file in /var/log
du -sh /var/log/* 2>/dev/null | sort -h | tail -5

# Look at a config file in /etc
cat /etc/hostname

# Check your home directory
ls -la ~

Part 2: Scenario-Based Practice (40 minutes)

Important: Focus on understanding the troubleshooting flow, not memorizing commands. Use the hints!

SOLVED EXAMPLE: Understanding How to Approach Scenarios

Example Scenario: Check if a service is running

Question: How do you check if the 'nginx' service is running?

My Solution (Step by step):

Step 1: Check service status

systemctl status nginx

Why this command? It shows if the service is active, failed, or stopped

Step 2: If service is not found, list all services

systemctl list-units --type=service

Why this command? To see what services exist on the system

Step 3: Check if service is enabled on boot

systemctl is-enabled nginx

Why this command? To know if it will start automatically after reboot

What I learned: Always check status first, then investigate based on what you see.

Now try these scenarios yourself:

Scenario 1: Service Not Starting

A web application service called 'myapp' failed to start after a server reboot.
What commands would you run to diagnose the issue?
Write at least 4 commands in order.

Hint:

  • First check: Is the service running or failed?
  • Then check: What do the logs say?
  • Finally check: Is it enabled to start on boot?

Commands to explore: systemctl status myapp, myapp, journalctl -u myapp -n 50systemctl is-enabled

Resource: Review Day 04 (Process and Services practice)

Template for your answer:

Step 1: [command]
Why: [one line explanation]

Step 2: [command]
Why: [one line explanation]

...

Scenario 2: High CPU Usage

Your manager reports that the application server is slow.
You SSH into the server. What commands would you run to identify
which process is using high CPU?

Hint:

  • Use a command that shows live CPU usage
  • Look for processes sorted by CPU percentage
  • Note the PID (Process ID) of the top process

Commands to explore: top (press 'q' to quit), htop, ps aux --sort=-%cpu | head -10

Resource: Review Day 05 (Troubleshooting Drill - CPU & Memory section)

Scenario 3: Finding Service Logs

A developer asks: "Where are the logs for the 'docker' service?"
The service is managed by systemd.
What commands would you use?

Hint:

  • systemd services → logs are in journald
  • Command pattern: journalctl -u <service-name>
  • Use -n flag to limit number of lines
  • Use -f flag to follow logs in real-time (like tail -f)

Commands to explore:

# Check service status first
systemctl status ssh

# View last 50 lines of logs
journalctl -u ssh -n 50

# Follow logs in real-time
journalctl -u ssh -f

Resource: Review Day 04 (Process and Services - Log checks section)

Scenario 4: File Permissions Issue

A script at /home/user/backup.sh is not executing.
When you run it: ./backup.sh
You get: "Permission denied"

What commands would you use to fix this?

Hint:

  • First: Check what permissions the file has
  • Understand: Files need 'x' (execute) permission to run
  • Fix: Add execute permission with chmod

Step-by-step solution structure:

Step 1: Check current permissions
Command: ls -l /home/user/backup.sh
Look for: -rw-r--r-- (notice no 'x' = not executable)

Step 2: Add execute permission
Command: chmod +x /home/user/backup.sh

Step 3: Verify it worked
Command: ls -l /home/user/backup.sh
Look for: -rwxr-xr-x (notice 'x' = executable)

Step 4: Try running it
Command: ./backup.sh

Resource: Review Day 02 (File Permissions and Users Management)

Why This Matters for DevOps

Understanding the file system is critical for:

  • Knowing where to find logs, configs, and binaries
  • Troubleshooting deployment issues
  • Writing automation scripts that work across systems

Scenario-based practice prepares you for:

  • Real production incidents
  • DevOps interviews
  • On-call troubleshooting under pressure

These are questions you will face in interviews and during real incidents.

Submission

  1. Fork this 90DaysOfDevOps repository
  2. Navigate to the 2026/day-07/ folder
  3. Add your day-07-linux-fs-and-scenarios.md file
  4. Commit and push your changes to your fork

Learn in Public

Share your Day 07 progress on LinkedIn:

  • Post 2–3 lines on what you learned about Linux file system
  • Share one scenario you found challenging and how you solved it
  • Optional: screenshot of your notes

Use hashtags:

#90DaysOfDevOps
#DevOpsKaJosh
#TrainWithShubham

Happy Learning TrainWithShubham