High CPU or Memory Usage

Is your server slow or unresponsive? Learn how to identify resource-intensive processes and resolve high CPU or memory usage issues.

1. Identifying Resource Usage
2. High CPU Usage Solutions
3. High Memory Usage Solutions
4. Long-term Monitoring
5. Prevention Tips

1 Identifying Resource Usage

Quick System Overview

# Quick resource check
top

# Better alternative with colors
htop

# Simple memory check
free -h

# CPU and load averages
uptime

Using htop (Recommended)

# Install htop if not available
sudo apt install htop -y

# Run htop
htop

Understanding htop Display:

• CPU bars: Each bar represents one CPU core
• Mem bar: Shows RAM usage
• Swp bar: Shows swap usage (should be low)
• Load average: 1-min, 5-min, 15-min averages
• Process list: Sorted by CPU or memory usage

Find Top Resource Consumers

# Top 10 CPU consuming processes
ps aux --sort=-%cpu | head -11

# Top 10 memory consuming processes
ps aux --sort=-%mem | head -11

# Processes using most CPU right now
top -b -n 1 | head -20

2 High CPU Usage Solutions

Common Causes

Runaway Process

A single process consuming excessive CPU

Solution:

# Find the process ID (PID)
ps aux --sort=-%cpu | head -5

# Kill the process
sudo kill -9 PID_NUMBER

# Or use htop: press F9, select signal, press Enter

Web Server Overload

Too many simultaneous connections or requests

Solutions:

# Check active connections
netstat -an | grep :80 | wc -l
netstat -an | grep :443 | wc -l

# Restart web server
sudo systemctl restart nginx
# or
sudo systemctl restart apache2

• Enable caching (Redis, Memcached)
• Optimize database queries
• Use a CDN for static content
• Consider upgrading VPS plan

Database Issues

MySQL/PostgreSQL using high CPU

Check slow queries:

# MySQL: Enable slow query log
sudo nano /etc/mysql/mysql.conf.d/mysqld.cnf

# Add these lines:
slow_query_log = 1
slow_query_log_file = /var/log/mysql/slow.log
long_query_time = 2

# Restart MySQL
sudo systemctl restart mysql

# View slow queries
sudo tail -f /var/log/mysql/slow.log

Malware or Mining Scripts

Cryptomining malware consuming resources

Check for suspicious processes:

# Look for unusual processes
ps aux | grep -E 'xmr|miner|crypto'

# Check for suspicious network connections
sudo netstat -tunap | grep ESTABLISHED

# Scan for rootkits
sudo apt install rkhunter -y
sudo rkhunter --check

Limit Process CPU Usage

# Use 'nice' to run with lower priority
nice -n 19 ./resource-heavy-script.sh

# Limit CPU with cpulimit
sudo apt install cpulimit -y
cpulimit -p PID -l 50  # Limit to 50% CPU

# Or use systemd to limit service
sudo systemctl set-property nginx.service CPUQuota=50%

3 High Memory Usage Solutions

Check Memory Status

# Detailed memory info
free -h

# Memory by process
ps aux --sort=-%mem | head -10

# Show swap usage
swapon --show

Understanding Memory Output

Linux caches frequently used files in RAM. "Available" memory is what matters, not "free". If "available" is low, you have a problem.

Common Memory Issues

Memory Leak in Application

Application continuously allocating memory without releasing it

# Monitor memory over time
watch -n 1 free -h

# Restart the problematic service
sudo systemctl restart service-name

# For persistent issues, schedule automatic restarts
# Edit crontab: sudo crontab -e
# Add: 0 3 * * * systemctl restart service-name

Clear Cache

Safe to do, won't hurt performance

# Drop caches (safe operation)
sync
echo 3 | sudo tee /proc/sys/vm/drop_caches

# Clear swap (if enabled)
sudo swapoff -a
sudo swapon -a

Add or Increase Swap

Temporary solution for occasional spikes

# Create 2GB swap file
sudo fallocate -l 2G /swapfile
sudo chmod 600 /swapfile
sudo mkswap /swapfile
sudo swapon /swapfile

# Make permanent
echo '/swapfile none swap sw 0 0' | sudo tee -a /etc/fstab

# Adjust swappiness (lower = use RAM more)
sudo sysctl vm.swappiness=10
echo 'vm.swappiness=10' | sudo tee -a /etc/sysctl.conf

Optimize MySQL Memory

sudo nano /etc/mysql/mysql.conf.d/mysqld.cnf

# For 2GB RAM VPS, add/modify:
[mysqld]
innodb_buffer_pool_size = 512M
key_buffer_size = 128M
max_connections = 50
query_cache_size = 32M
tmp_table_size = 32M
max_heap_table_size = 32M

# Restart MySQL
sudo systemctl restart mysql

Optimize PHP-FPM Memory

sudo nano /etc/php/8.1/fpm/pool.d/www.conf

# Adjust these values based on your RAM:
pm = dynamic
pm.max_children = 10
pm.start_servers = 2
pm.min_spare_servers = 1
pm.max_spare_servers = 3
pm.max_requests = 500

# Restart PHP-FPM
sudo systemctl restart php8.1-fpm

4 Long-term Monitoring

Install Monitoring Tools

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

# Enable data collection
sudo systemctl enable sysstat
sudo systemctl start sysstat

# View CPU usage history
sar -u

# View memory history
sar -r

# View all stats for today
sar -A

Create Monitoring Script

sudo nano /usr/local/bin/resource-monitor.sh

Add this script:

#!/bin/bash
LOG="/var/log/resource-monitor.log"
DATE=$(date '+%Y-%m-%d %H:%M:%S')

CPU=$(top -bn1 | grep "Cpu(s)" | awk '{print $2}' | cut -d'%' -f1)
MEM=$(free | grep Mem | awk '{print ($3/$2) * 100.0}')

echo "$DATE - CPU: ${CPU}% | Memory: ${MEM}%" >> $LOG

# Alert if CPU > 80%
if (( $(echo "$CPU > 80" | bc -l) )); then
    echo "HIGH CPU ALERT: $CPU%" | mail -s "Server Alert" [email protected]
fi

# Make executable
sudo chmod +x /usr/local/bin/resource-monitor.sh

# Run every 5 minutes via cron
sudo crontab -e
# Add: */5 * * * * /usr/local/bin/resource-monitor.sh

5 Prevention Tips

Optimize Applications

• Enable caching (Redis, Memcached)
• Optimize database queries
• Minify CSS/JS files
• Use CDN for static content
• Enable gzip compression

Security Measures

• Keep software updated
• Use fail2ban for brute force protection
• Regular security audits
• Monitor for unusual activity
• Disable unused services

Right-Size Your Server

• Monitor usage patterns
• Upgrade when consistently >70% usage
• Consider Streaming VPS for media
• Dedicated servers for high traffic

Regular Maintenance

• Clean up old logs regularly
• Remove unused packages
• Restart services periodically
• Monitor disk space
• Update and reboot monthly

When to Upgrade

If you're consistently using >70% of CPU or memory even after optimization, it's time to upgrade your VPS plan. X-ZoneServers makes scaling easy with no downtime!

Still Experiencing Issues?

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