Whether you’re managing servers, troubleshooting applications, or simply trying to understand what’s going on under the hood, knowing key Linux commands is essential for anyone working in IT. Below is a curated list of commands with real-world use cases to help you understand not just the how, but the why behind each one.
1. top
Use it for: Monitoring system performance in real time
Why: It provides a live view of CPU, memory, and process usage. When troubleshooting performance issues, top helps you quickly identify resource-hungry processes.
2. ps aux
Use it for: Viewing running processes
Why: If you suspect a service is hanging or misbehaving, this command gives a snapshot of what’s currently running — and under which user.
3. df -h
Use it for: Checking disk space
Why: Disk space issues can bring services to a halt. This command tells you which partitions are filling up in human-readable form.
4. du -sh *
Use it for: Finding large directories
Why: If you’re trying to free up space, this helps you identify which folders are consuming the most storage.
5. free -m
Use it for: Viewing memory usage
Why: Memory leaks and exhausted RAM are common problems. free -m shows current RAM and swap usage, helping you identify pressure points.
6. tail -f /var/log/syslog (or any log file)
Use it for: Watching logs in real time
Why: Critical for debugging and monitoring. This lets you see what’s happening the moment it’s logged — ideal for tracking errors or watching services start.
7. grep
Use it for: Searching within files or outputs
Why: Whether you’re scanning logs or looking for a specific config setting, grep helps you find exactly what you’re looking for.
Example:
bashCopyEditgrep "ERROR" /var/log/syslog
8. chmod and chown
Use it for: Setting file permissions and ownership
Why: Permissions are foundational for Linux security. If a file isn’t executing or a user can’t access something, chmod and chown are likely your fix.
9. scp
Use it for: Securely copying files between systems
Why: A secure way to transfer files between local and remote machines — often used for backups, log transfers, or deployments.
10. rsync
Use it for: Efficient file syncing
Why: Unlike scp, rsync only transfers changed parts of files, making it ideal for backups and remote sync operations.
11. systemctl
Use it for: Managing services
Why: Start, stop, restart, or check the status of services. A must-know for managing daemons like nginx, mysql, or custom apps.
Example:
bashCopyEditsudo systemctl restart nginx
12. netstat -tuln or ss -tuln
Use it for: Checking listening ports and services
Why: Useful when debugging network connectivity or making sure your service is actually running and listening.
13. crontab -e
Use it for: Scheduling recurring tasks
Why: Automate log rotations, backups, or script execution with cron jobs.
14. uptime
Use it for: Checking how long the system has been running
Why: Good for understanding server stability and spotting recent reboots.
15. uname -a
Use it for: Viewing system/kernel info
Why: Helpful when verifying kernel versions or debugging compatibility issues.
16. ls -l
Use it for: Listing files and directories with detailed information
Why: Unlike a plain ls, this command shows file permissions, ownership, size, and modification date. It’s essential for understanding access rights, file sizes, and when things were last changed especially when debugging file-level issues.
Example output:
cssCopyEdit-rw-r--r-- 1 user user 4096 Aug 2 12:34 example.txt
You can place this right after 15. uname -a, or reorder it however you’d like. Let me know if you’d like a downloadable version of the full article or an image-based summary (e.g., infographic or cheat sheet).
Final Thoughts
Mastering Linux commands isn’t about memorizing everything — it’s about understanding the intent behind each one. Start with the commands you use most often and expand from there. Whether you’re in DevOps, SRE, or general IT, these tools are your first line of defense when problems arise.
Here’s a clean, copy-ready list of all the Linux commands mentioned — perfect for pasting into a Notepad or saving as a cheat sheet:
pgsqlCopyEdit1. top - Monitor system performance in real time
2. ps aux - View all running processes
3. df -h - Check disk space in human-readable format
4. du -sh * - Show disk usage of each directory
5. free -m - Check memory usage in megabytes
6. tail -f /var/log/syslog - View logs in real time
7. grep "ERROR" /var/log/syslog - Search for "ERROR" in a log file
8. chmod 755 filename - Change file permissions
9. chown user:group filename - Change file ownership
10. scp file.txt user@host:/path - Securely copy files between systems
11. rsync -avz source/ destination/ - Efficient file syncing
12. systemctl status servicename - Check the status of a service
13. systemctl restart servicename - Restart a service
14. netstat -tuln - Show open ports and listening services
15. ss -tuln - Faster alternative to netstat
16. crontab -e - Edit the cron job schedule
17. uptime - Show how long the system has been running
18. uname -a - Display detailed system information
19. ls -l - List directory contents with details
Mitchell Lyon 