How to Fix High CPU Usage on Linux Server

High CPU usage slows down or crashes your server. Finding the exact cause quickly is essential — this guide covers systematic diagnosis and fixes.

Step 1 — Identify the Process

# Real-time CPU usage
top -c
# Press P to sort by CPU
# Press 1 to see per-core usage

# More detailed view
htop

# Non-interactive snapshot
ps aux --sort=-%cpu | head -20

Step 2 — Fix PHP-FPM High CPU

# Too many PHP-FPM workers spinning
ps aux | grep php-fpm | wc -l

# Check for infinite loops in PHP
sudo strace -p PHP_PID 2>&1 | head -20

# Restart PHP-FPM
sudo systemctl restart php8.2-fpm

# Reduce workers if overloaded
pm.max_children = 20
pm.max_requests = 500  # Restart workers after 500 requests

Step 3 — Fix MySQL High CPU

# Check for long-running queries
mysql -u root -p -e "SHOW PROCESSLIST;"

# Kill CPU-intensive query
mysql -u root -p -e "KILL QUERY process_id;"

# Check for missing indexes causing full table scans
mysql -u root -p -e "SHOW STATUS LIKE 'Select_full_join';"

Step 4 — Fix WP-Cron CPU Spikes

# WP-Cron running too frequently
grep "wp-cron" /var/log/nginx/access.log | wc -l

# Disable WP-Cron and use real cron
define('DISABLE_WP_CRON', true);

# Add to real cron
*/5 * * * * wp --path=/var/www/html cron event run --due-now --quiet

Step 5 — Check for Malware Using CPU

# Suspicious processes using high CPU
ps aux --sort=-%cpu | head -20
# Check any unknown processes

# Check for crypto miners
ps aux | grep -E "minerd|xmrig|cpuminer|kworker"

# Check network connections for mining pools
netstat -tulpn | grep -E "3333|4444|5555|8333"

Step 6 — Fix Runaway Cron Jobs

# Check all crontabs
crontab -l
sudo crontab -l
cat /etc/crontab
ls /etc/cron.d/

# Check currently running cron jobs
ps aux | grep cron

Conclusion

High CPU issues need immediate identification and fixing. Our team provides emergency server performance support with 15-minute response time.