Basics interview questions and answers for Linux admin L2 ✅ 1. What is the difference between a hard link and a soft link? Answer: • Hard Link: • Points directly to the inode of a file. • Even if the original file is deleted, the data is accessible via the hard link. • Cannot span across filesystems. • Soft Link (Symbolic Link): • Points to the file name/path. • If the original file is deleted, the link becomes broken. • Can span filesystems and directories. ✅ 2. How do you check disk usage in Linux? Answer: Use the df and du commands: • df -h: Shows disk space usage of file systems. • du -sh /path/to/dir: Shows the size of a specific directory. ✅ 3. How do you check and kill a process using the command line? Answer: • Find the process: • ps aux | grep process_name • top or htop • Kill the process: • kill PID — gracefully. • kill -9 PID — forcefully ✅ 4. How do you check which ports are listening on a Linux server? Answer: • netstat -tuln (older systems) • ss -tuln (newer systems) • lsof -i (to see which process is using which port) ✅ 5. How do you check CPU and memory usage? Answer: • CPU: • top or htop • mpstat (from sysstat package) • Memory: • free -m • vmstat • top ✅ 6. What is a runlevel? Answer: • A runlevel defines the state of the machine after boot. • Common runlevels: • 0: Halt • 1: Single-user mode • 3: Multi-user, no GUI • 5: Multi-user with GUI • 6: Reboot • On systemd systems, runlevels are replaced by targets (e.g., multi-user.target) ✅ 7. How to schedule a cron job? Answer: • Use crontab -e to edit user’s cron jobs. • Example: 0 2 * * * /path/to/script.sh (Runs daily at 2 AM) ✅ 8. How to check system logs? Answer: • Use journalctl (on systemd systems) • Or view log files in /var/log/ • messages, syslog, dmesg, secure, auth.log ✅ 9. How to extend a logical volume? Answer: • lvextend -L +10G /dev/mapper/vgname-lvname resize2fs /dev/mapper/vgname-lvname Or if using XFS: • xfs_growfs /mount/point ✅ 10. What is the difference between init and systemd? Answer: • init: Traditional SysV init system (serial startup). • systemd: Modern init system (parallel service startup, faster boot, uses journalctl for logs). • systemctl is used to manage services in systemd. ✅ 11. How do you change the hostname of a Linux system? Answer: • Temporarily: hostname new-name • Permanently (systemd): dd if=/dev/zero of=/swapfile bs=1G count=2 chmod 600 /swapfile mkswap /swapfile swapon /swapfile ✅ 13. How do you check SELinux status? Answer: • sestatus • Enforcing: SELinux is active and enforcing rules. • Permissive: Logs actions that would be denied. • Disabled: Not running. ✅14. What is /etc/fstab used for? Answer: • Defines how disk partitions, storage devices, and remote filesystems are mounted at boot. • Example entry: /dev/sda1 / ext4 defaults 0 1