1. How to Check Disk Space Usage
Answer:
Use
df -h to view disk usage by mounted filesystems. For directory-level details, run du -sh /path/to/directory. Clean up old logs, unused packages, or large files with tools like ncdu for interactive analysis.2. Service Fails to Start
Answer:
Check status with
systemctl status service-name. View logs via journalctl -u service-name --since "10 minutes ago". Ensure dependencies are installed and configuration files (e.g., /etc/service-name/config.conf) are correct.3. Network Connectivity Issues
Answer:
- Test connectivity:
ping 8.8.8.8 (Google DNS). - Check routes:
ip route or traceroute google.com. - Verify DNS:
dig google.com or nslookup google.com. - Inspect interfaces:
ip a or ifconfig. Restart networking with systemctl restart NetworkManager (or networkd).4. "Permission Denied" Errors
Answer:
- Check permissions:
ls -l /path/to/file. - Modify permissions:
chmod 755 file or chown user:group file. - If SELinux/AppArmor blocks access, check logs (
/var/log/audit/audit.log) or temporarily disable with setenforce 0.5. Terminating Unresponsive Processes
Answer:
- Find PID:
ps aux | grep process-name or top. - Kill process:
kill -9 PID or pkill process-name. - Force-kill all instances:
killall -9 process-name.6. System Fails to Boot
Answer:
- Boot into recovery mode (GRUB menu) and check logs (
/var/log/boot.log or journalctl -b). - Repair filesystems:
fsck /dev/sdX. - Reinstall bootloader (GRUB):
grub-install /dev/sdX.7. "No Space Left on Device" Despite Free Space
Answer:
- Check inode usage:
df -i. - Delete small, numerous files (e.g., temporary files) to free inodes.
8. DNS Resolution Failures
Answer:
- Verify DNS config:
cat /etc/resolv.conf. - Test DNS server:
dig @8.8.8.8 google.com. - Restart DNS resolver:
systemctl restart systemd-resolved.9. High CPU/Memory Usage
Answer:
- Identify resource hogs:
top, htop, or vmstat 2. - Kill problematic processes or optimize applications. Check for memory leaks with
free -h.10. SSH Connection Refused
Answer:
- Ensure SSH service runs:
systemctl status sshd. - Check firewall rules:
ufw status or iptables -L. - Verify SSH port (default: 22) is open and accessible.
11. Filesystem Corruption
Answer:
- Unmount the disk:
umount /dev/sdX. - Run
fsck /dev/sdX to repair. Backup critical data first. For root FS, boot from a live USB.12. Cron Jobs Not Executing
Answer:
- Check cron logs:
grep CRON /var/log/syslog. - Ensure the cron service is running:
systemctl status cron. - Validate syntax and user permissions in
/etc/crontab or user crontabs (crontab -e).
