1. How do you check system performance? Use multiple tools depending on need: top htop uptime vmstat 1 iostat -x 1 free -m sar -u 1 5 👉 Real-time: CPU bottleneck → check top & vmstat 2. How do you find high CPU consuming process? top ps -eo pid,ppid,cmd,%mem,%cpu --sort=-%cpu | head Kill process: kill -9 3. How do you check memory usage? free -m cat /proc/meminfo top 4. Difference between soft link & hard link? ln file1 hardlink ln -s file1 softlink Hard link → same inode Soft link → pointer (like shortcut) 5. How do you find large files? find / -type f -size +100M du -ah / | sort -rh | head -20 6. How do you monitor logs in real-time? tail -f /var/log/messages tail -f /var/log/syslog 7. What is inode? Check inode: ls -i df -i 👉 Stores metadata of file 8. How do you manage disk space? df -h du -sh * Clean: rm -rf unwanted_files 9. How do you check open ports? netstat -tulnp ss -tulnp 10. How do you check running services? systemctl status nginx systemctl list-units --type=service 11. How do you restart a service? systemctl restart nginx 12. What is cron job? How to schedule? crontab -e Example: 0 2 * * * /backup.sh 13. How do you find file by name? find / -name file.txt locate file.txt 14. How do you check disk I/O? iostat -x 1 iotop 15. What is load average? uptime 👉 Load > CPU cores → system overloaded 16. How do you change permissions? chmod 755 file chmod +x script.sh 17. How do you change ownership? chown user:group file 18. How do you troubleshoot server down issue? Step-by-step: Check server access: ping ssh user@ip Check CPU/memory: top free -m Check disk: df -h Check logs: tail -f /var/log/messages 19. How do you check network connectivity? ping google.com traceroute google.com curl -I http://example.com 20. What is grep? Give example grep "error" file.log grep -i "failed" file.log grep -r "password" /etc 21. How do you compress files? tar -cvf file.tar dir/ tar -xvf file.tar gzip file gunzip file.gz 22. What is process management? ps -ef kill nice renice 23. What is swap memory? Check: swapon -s free -m 24. Difference between TCP & UDP? TCP → reliable UDP → fast but no guarantee 25. How do you check OS version? cat /etc/os-release uname -a 💥 Real-Time Scenario Questions 🔹 Scenario 1: Disk full df -h du -sh * find / -size +500M 🔹 Scenario 2: Server slow top vmstat iostat 🔹 Scenario 3: Service not starting systemctl status nginx journalctl -xe 🔹 Scenario 4: Port not accessible netstat -tulnp ss -tulnp firewall-cmd --list-all ⚡

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