Day 3 - Linux Command Cheat Sheet for DevOps

📊 Process & Resource Management

• top: Displays real-time system resource usage and active processes.

• htop: Interactive process viewer (more user-friendly than top).

• ps aux: Shows a detailed snapshot of all running processes.

• kill -9 <PID>: Forcefully terminates a process using its ID.

• lsof -i :80: Shows which process is using port 80 (crucial for web servers).

• free -m: Displays used and free RAM in Megabytes.

• uptime: Shows how long the system has been running and the load average.

📂 File System & Navigation

• ls -lah: Lists all files (including hidden) with human-readable sizes.

• pwd: Prints the current working directory path.

• cd ..: Moves one level up in the directory structure.

• mkdir -p /path/to/dir: Creates nested directories in one go.

• cp -r: Copies directories and their contents recursively.

• mv: Moves or renames files and directories.

• rm -rf: Forcefully and recursively removes files/folders (Use with caution!).

• find / -name "app.log": Searches for a specific file starting from the root.

• du -sh *: Summarizes disk usage of each folder in the current directory.

• df -h: Shows disk space usage across all mounted file systems.

• grep -i "error" log.txt: Searches for the string "error" inside a file (case-insensitive).

• tail -f /var/log/syslog: Watches a log file in real-time as new entries are added.

• chmod 644 file.txt: Sets standard read/write permissions for a file.

🌐 Networking Troubleshooting

• ping <host>: Checks basic connectivity between your machine and a server.

• ip addr show: Displays IP addresses and network interface details.

• curl -I <url>: Fetches the HTTP header of a website (great for debugging 404/500 errors).

• dig <domain>: Performs a DNS lookup to check domain-to-IP mapping.

• netstat -tulpn: Lists all listening ports and the programs using them.

• ssh user@ip: Securely connects to a remote server.