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Introduction
Linux is the backbone of modern DevOps, cloud computing, and cybersecurity. Whether you’re preparing for an interview or sharpening your skills, understanding Linux commands and system administration is crucial. This guide covers beginner to advanced Linux interview questions, along with practical command examples to help you succeed.
Learning Objectives
- Understand fundamental Linux commands for system administration.
- Learn troubleshooting techniques for performance and security.
- Master advanced Linux concepts like process management and kernel tuning.
1. Linux File System and Basic Commands
Viewing Hidden Files
ls -a
What it does: Lists all files, including hidden ones (those starting with a dot).
How to use:
ls -a /home/user
Checking Disk Usage
df -h
What it does: Displays disk space usage in a human-readable format.
How to use:
df -h /dev/sda1
2. Process and System Monitoring
Checking Running Processes
top
What it does: Shows real-time system processes, CPU, and memory usage.
How to use:
- Press `q` to quit.
- Press `Shift + M` to sort by memory usage.
Killing a Process
kill -9 [bash]
What it does: Forcefully terminates a process.
How to use:
1. Find the process ID (PID) with:
ps aux | grep "process_name"
2. Kill it:
kill -9 1234
3. Networking and Security
Checking Open Ports
netstat -tuln
What it does: Lists all listening ports.
Alternative (modern Linux systems):
ss -tuln
Setting Up SSH Key Authentication
ssh-keygen -t rsa -b 4096
What it does: Generates a secure SSH key pair.
How to use:
1. Generate keys:
ssh-keygen -t rsa -b 4096
2. Copy the public key to a remote server:
ssh-copy-id user@remote-server
4. File Permissions and Security
Changing File Permissions
chmod 755 filename
What it does: Sets read, write, and execute permissions.
– `7` (owner): Read + Write + Execute
– `5` (group/others): Read + Execute
How to use:
chmod 755 /var/www/html/index.html
Using `sudo` vs. `su`
– `sudo` executes a command with superuser privileges.
– `su` switches to the root user entirely.
Example:
sudo apt update
5. Advanced Troubleshooting
Debugging a Slow System
vmstat 1
What it does: Displays system performance metrics (CPU, memory, I/O).
Alternative:
iostat -xz 1
Checking Failed Services
journalctl -xe
What it does: Displays system logs for troubleshooting service failures.
What Undercode Say
- Key Takeaway 1: Mastering Linux commands is essential for DevOps, cloud, and cybersecurity roles.
- Key Takeaway 2: Understanding system internals (like
systemd,cgroups, and kernel tuning) separates junior from senior engineers.
Analysis:
Linux remains the dominant OS in cloud and infrastructure. Employers prioritize candidates who can debug performance issues, secure systems, and automate tasks. With cloud adoption rising, Linux expertise ensures career longevity.
Prediction
As cloud-native technologies (Kubernetes, serverless) grow, Linux skills will become even more critical. Expect increased demand for engineers who can optimize containers, harden kernels, and automate deployments at scale.
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