Diagnosing High CPU Usage on Your VPS

Identify the Problem

# Quick overview
top -bn1 | head -20

# Sort by CPU usage
top -o %CPU

# More detailed view
htop

Find the Offending Process

# Top CPU consumers
ps aux --sort=-%cpu | head -10

# CPU usage by process name
pidstat -u 5 3  # Sample every 5 seconds, 3 times

Common Causes and Solutions

1. Runaway PHP Process

# Find PHP processes
ps aux | grep php

# Check PHP-FPM status
systemctl status php8.2-fpm

# Kill a specific stuck process
kill -9 PID

Fix: Check for infinite loops, unoptimized database queries, or missing indexes.

2. Database Queries

# Check MySQL process list
mysql -e "SHOW PROCESSLIST;"

# Find slow queries
mysql -e "SHOW FULL PROCESSLIST;" | grep -v Sleep

Fix: Add indexes, optimize queries, enable query caching.

3. Bot/Crawler Traffic

# Check web server access logs for high-frequency IPs
awk '{print $1}' /var/log/nginx/access.log | sort | uniq -c | sort -rn | head -20

Fix: Block abusive IPs with a firewall or use rate limiting.

4. Cryptocurrency Mining Malware

# Check for suspicious processes
top -bn1 | grep -E "(xmrig|minerd|cryptonight)"

# Check crontabs
crontab -l
ls -la /etc/cron.d/

Fix: Kill the process, remove from crontab, check for compromised accounts, change all passwords.

Long-Term Monitoring

# Install sysstat for historical data
sudo apt install -y sysstat

# View CPU history
sar -u 1 10  # 10 samples, 1 second apart

# View historical data
sar -u -f /var/log/sysstat/sa$(date +%d -d yesterday)