Day 16 of My DevOps Journey — Practical Linux Administration for DevOps

Linux is the backbone of DevOps, and today I focused on applying fundamentals in a way that mirrors real-world tasks. I worked hands-on with EC2 Ubuntu instances, covering user management, permissions, environment setup, inter-server communication, and automation with shell scripting.

Instead of treating them as isolated exercises, I approached each task as if I were managing servers in production.

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Task 1: Secure User & SSH Setup

Problem: In real-world environments, giving every engineer direct root access is a security risk. The correct approach is to create dedicated users with SSH keys.

Steps I took:

# Create a new user
sudo adduser devopsuser  

# Create SSH directory for the user
sudo mkdir /home/devopsuser/.ssh  

# Add the public key for secure access
sudo nano /home/devopsuser/.ssh/authorized_keys  

# Set correct permissions
sudo chown -R devopsuser:devopsuser /home/devopsuser/.ssh  
sudo chmod 600 /home/devopsuser/.ssh/authorized_keys

Learning: Permissions and ownership are crucial. Without correct chmod 600, SSH will reject the key for being insecure.

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Task 2: File & Directory Permissions

Problem: On shared servers, we need to ensure files and directories are owned and accessible only by intended users or groups.

Steps I took:

# Create files and directories
sudo touch project.txt  
sudo mkdir project_dir  

# Assign ownership to the new user
sudo chown devopsuser:devopsuser project.txt project_dir  

# Restrict access to owner and group
sudo chmod 770 project_dir

Learning: A single misconfigured permission can cause unauthorized access or, worse, expose sensitive files. Practicing this taught me how least privilege access works in Linux.

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Task 3: Environment Setup — JDK Installation

Problem: Many applications require Java. Without setting JAVA_HOME, build tools like Maven won’t work properly.

Steps I took:

# Install JDK
sudo apt update -y  
sudo apt install -y openjdk-11-jdk  

# Set JAVA_HOME and persist it
echo "export JAVA_HOME=/usr/lib/jvm/java-11-openjdk-amd64" >> ~/.bashrc  
source ~/.bashrc  

# Verify installation
java -version

Challenge: JAVA_HOME worked in the current session but disappeared after reboot. I solved this by exporting it permanently in .bashrc.

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Task 4: Instance-to-Instance Communication

Problem: In a real deployment, multiple servers need to exchange data securely. Testing this with two EC2 instances gave me hands-on exposure.

Steps I took:

# Copy file securely from Instance A to Instance B
scp -i key.pem file.txt ubuntu@<instance-b-ip>:/home/ubuntu/

Learning: SCP is the simplest way to test secure data transfer. For large-scale systems, we would use more advanced tools, but this was a strong foundation.

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Task 5: Automation with Shell Scripting

Problem: Manually installing dependencies wastes time and creates inconsistency. Automation ensures uniform setups across servers.

Solution Script:

#!/bin/bash
echo "Updating Ubuntu packages..."
sudo apt update -y

echo "Installing Git..."
sudo apt install git -y

echo "Installing Java JDK 11..."
sudo apt install -y openjdk-11-jdk

echo "Installing Maven..."
sudo apt install -y maven

echo "Installation Complete!"
echo "Installed Versions:"
git --version
java --version
mvn --version

Challenge: The script initially failed because I typed mvn--version (without a space). Debugging line-by-line helped me fix it.

Learning: Small syntax issues can break automation. Testing scripts step by step is critical.

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Challenges I Faced

• Permission Errors: Forgot to use sudo → Solved by re-running with elevated privileges.

• JAVA_HOME Persistence: Variable disappeared → Fixed by adding it to .bashrc.

• SSH Rejection: Public key not set up → Solved by placing the key in authorized_keys.

• Script Debugging: Wrong syntax caused failure → Debugged carefully and fixed.

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Key Takeaways

1. Linux administration is about security, automation, and precision.

2. Debugging small mistakes builds problem-solving skills that scale up to complex systems.

3. Every command connects back to real DevOps practices — user management, secure transfers, environment setup, and automation.