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Comprehensive System Monitoring

Check system resources, disk usage, and running processes with these essential Ubuntu commands. Perfect for diagnosing performance issues on your VPS or local machine.

1. Real-Time System Resource Monitor

Monitor CPU, memory, and processes in real-time with htop (more user-friendly than top):

sudo apt install htop -y && htop

2. Disk Usage Analysis

Find the largest directories consuming disk space:

# Show top 10 largest directories in /
sudo du -h / 2>/dev/null | sort -rh | head -n 10

# Or use ncdu for interactive browsing
sudo apt install ncdu -y
sudo ncdu /

3. Memory Usage Breakdown

View detailed memory usage including cache and buffers:

# Detailed memory info
free -h

# Show top memory-consuming processes
ps aux --sort=-%mem | head -n 10

System Cleanup Commands

4. Complete Package Cleanup

Remove unnecessary packages, clean apt cache, and reclaim disk space:

# Full cleanup chain
sudo apt autoremove -y && \
sudo apt autoclean -y && \
sudo apt clean -y && \
sudo journalctl --vacuum-time=3d && \
sudo rm -rf /tmp/* 2>/dev/null

echo "Cleanup complete!"

5. Find and Remove Old Kernels

Safely remove old kernel versions (keep current + 1 previous):

# List installed kernels
dpkg --list | grep linux-image

# Remove old kernels (interactive)
sudo apt autoremove --purge

6. Clear System Logs

Reduce systemd journal size and clear old logs:

# Limit journal to 100MB
sudo journalctl --vacuum-size=100M

# Keep only last 2 days of logs
sudo journalctl --vacuum-time=2d

# Check current journal size
journalctl --disk-usage

Performance Monitoring

7. Check Network Connections

View active network connections and listening ports:

# Show all listening ports
sudo netstat -tulpn | grep LISTEN

# Or use ss (faster, modern alternative)
sudo ss -tulpn | grep LISTEN

# Monitor real-time network usage
sudo apt install nethogs -y && sudo nethogs

8. Service Status Check

Check status of critical services:

# Check multiple services at once
for service in nginx postgresql ssh ufw; do
    systemctl is-active $service && \
    echo "✓ $service is running" || \
    echo "✗ $service is NOT running"
done

Pro Tips

• Run cleanup commands monthly or when disk space is low
• Always use sudo for system-level operations
• Create aliases in ~/.bashrc for frequently used commands
• Monitor systemd journal size - it can grow to several GB on busy servers

Analyzing Systemd Service Startup Times

systemd-analyze reveals exactly how long boot took and which services are responsible for the slowdown:

# Total boot time breakdown
systemd-analyze

# Per-service time sorted by slowest
systemd-analyze blame | head -20

# Visual SVG timeline (opens in browser)
systemd-analyze plot > /tmp/boot.svg

Services taking more than 3–5 seconds are candidates for disabling (if you don't need them) or masking. Disable with systemctl disable --now servicename. Common culprits on VPS servers: ModemManager, avahi-daemon, and multipathd.

Swap Management and Tuning

On systems with adequate RAM, swap should rarely be used. A high vm.swappiness value causes the kernel to swap aggressively, degrading performance:

# Check current swap usage
free -h && swapon --show

# Check swappiness (default is 60, server-optimal is 10)
cat /proc/sys/vm/swappiness

# Set it permanently
echo "vm.swappiness=10" | sudo tee -a /etc/sysctl.conf
sudo sysctl -p

If your server has 2 GB+ RAM and swap is consistently in use, the real fix is identifying the memory-hungry process with ps aux --sort=-%mem | head -10, not expanding swap.

Log Rotation and Journal Size Control

Systemd journals can grow unchecked on busy servers. Cap them to prevent disk fill:

# Check current journal size
journalctl --disk-usage

# Vacuum entries older than 30 days OR down to 500 MB
sudo journalctl --vacuum-time=30d
sudo journalctl --vacuum-size=500M

# Make the cap permanent
sudo nano /etc/systemd/journald.conf
# Set: SystemMaxUse=500M and MaxRetentionSec=1month
sudo systemctl restart systemd-journald

For traditional syslog (/var/log/), logrotate handles rotation. Check /etc/logrotate.d/ for per-service configs and logrotate -d /etc/logrotate.conf to do a dry run.

Fail2Ban: Automatic Brute-Force Protection

Fail2ban monitors logs and temporarily bans IPs that show malicious behavior — essential for any server with SSH exposed to the internet:

# Install and enable
sudo apt install fail2ban -y
sudo systemctl enable --now fail2ban

# Check banned IPs
sudo fail2ban-client status sshd

# Unban a specific IP (if you lock yourself out)
sudo fail2ban-client set sshd unbanip 1.2.3.4

Create /etc/fail2ban/jail.local to override defaults without touching jail.conf (which gets overwritten on updates). Recommended SSH settings: maxretry = 3, bantime = 1h, findtime = 10m.

Docker and Container Cleanup

If you run Docker, images, containers, and volumes accumulate silently. A full prune recovers significant disk space:

# What's taking space?
docker system df

# Remove stopped containers, dangling images, unused networks
docker system prune -f

# Also remove unused volumes (careful — this deletes data)
docker system prune --volumes -f

# Remove all unused images (not just dangling)
docker image prune -a -f

Schedule a weekly prune with cron: 0 3 * * 0 /usr/bin/docker system prune -f >> /var/log/docker-prune.log 2>&1