No matter how well you set up your VPS, things will go wrong—server crashes, security breaches, data corruption, or unexpected spikes in traffic. In this chapter, we’ll cover real-world VPS troubleshooting, diagnosing performance issues, preventing downtime, and disaster recovery strategies to bring your server back online quickly.
7.1 Diagnosing VPS Performance Issues
1️⃣ Checking CPU & RAM Usage
If your VPS is slow or unresponsive, the first step is to check CPU, memory, and disk usage.
Check System Resource Usage with top or htop
top
or
htop
Look at:
%CPU→ High values mean processes are overloading the CPU.%MEM→ High values indicate low available RAM.
Check Running Processes with ps
Find which processes are consuming the most resources:ps aux --sort=-%mem | head -10
Check Disk Space with df
df -h
If / or /var is full, it may cause server crashes.
Check I/O Bottlenecks with iotop
iotop
If a process is using too much disk I/O, it can slow down everything.
2️⃣ Fixing High CPU & Memory Usage
If your VPS is maxing out CPU or RAM:
Kill High-Usage Processes
kill -9 <PID>
Limit CPU Usage with cpulimit
apt install cpulimit -y
cpulimit -p <PID> -l 50
This limits a process to 50% CPU usage.
Increase Swap Memory (If RAM is Full)
fallocate -l 2G /swapfile
chmod 600 /swapfile
mkswap /swapfile
swapon /swapfile
echo '/swapfile none swap sw 0 0' >> /etc/fstab
7.2 Network Issues – Fixing Slow or Unreachable VPS
1️⃣ Checking Network Status
First, verify network connectivity:
ping 8.8.8.8 -c 4
If it fails, check your network configuration.
Check Open Ports
netstat -tulnp
Ensure your web server (Nginx/Apache) is listening on the correct port.
Check Firewall Rules
ufw status
iptables -L -n -v
If needed, allow traffic:
ufw allow 80/tcp
ufw allow 443/tcp
7.3 Fixing Web Server (Nginx/Apache) Issues
1️⃣ Check if the Web Server is Running
systemctl status nginx
systemctl status apache2
2️⃣ Restart the Web Server
systemctl restart nginx
systemctl restart apache2
3️⃣ Check Logs for Errors
tail -f /var/log/nginx/error.log
tail -f /var/log/apache2/error.log
4️⃣ Fixing “502 Bad Gateway” Errors
If Nginx shows 502 Bad Gateway, restart PHP:
systemctl restart php-fpm
5️⃣ Fixing “403 Forbidden” Errors
Check file permissions:
chmod -R 755 /var/www/html/
chown -R www-data:www-data /var/www/html/
7.4 Fixing Database (MySQL/PostgreSQL) Issues
1️⃣ Check if MySQL/PostgreSQL is Running
systemctl status mysql
systemctl status postgresql
Restart if needed:
systemctl restart mysql
systemctl restart postgresql
2️⃣ Fixing “Too Many Connections” Error
If MySQL rejects connections:SHOW STATUS WHERE variable_name = 'Threads_connected';
Increase limits:SET GLOBAL max_connections = 500;
3️⃣ Repair Corrupt MySQL Database
mysqlcheck -r database_name
7.5 Handling Server Crashes & Recovery
1️⃣ Rebooting a Frozen VPS
If the VPS is completely unresponsive:
reboot -f
If that doesn’t work, use your VPS provider’s control panel to force restart.
2️⃣ Recovering from a Kernel Panic
If your VPS crashes due to a bad kernel update, reboot into an older kernel:
- Reboot and select Advanced Options in GRUB.
- Choose an older kernel version.
- If successful, remove the faulty kernel:
dpkg –list | grep linux-image
apt remove linux-image-
update-grub
reboot
7.6 Preventing Downtime with Backup & Restore Strategies
1️⃣ Automated Daily Backups
Use rsync to back up files to another VPS:
rsync -avz /var/www/ user@backup-server:/backups/
2️⃣ MySQL Automatic Backups
Create a cron job to backup MySQL databases every night:
crontab -e
Add:
0 3 * * * mysqldump -u root -p'yourpassword' --all-databases > /backup/db-$(date +\%F).sql
3️⃣ Restoring from Backup
If a server crash happens, restore from backup:
scp user@backup-server:/backups/db-latest.sql /tmp/
mysql -u root -p < /tmp/db-latest.sql
7.7 Protecting Your VPS from DDoS Attacks
1️⃣ Install Fail2Ban to Block Attackers
apt install fail2ban -y
Enable it:
systemctl enable fail2ban --now
2️⃣ Use Cloudflare for DDoS Protection
- Set up Cloudflare free plan.
- Enable “Under Attack Mode” to filter traffic.
3️⃣ Block Malicious Traffic with IPTables
iptables -A INPUT -s <malicious-ip> -j DROP
Conclusion
Troubleshooting is a critical skill for VPS hosting. By learning how to diagnose issues, fix common problems, and prevent downtime, you can keep your VPS online and secure.
In the next chapter, we’ll explore Optimizing VPS for Speed & Performance, including advanced caching, fine-tuning database queries, and leveraging CDNs for lightning-fast websites.