Understanding Server Resource Monitoring

Why Monitor Resources?

Monitoring CPU, memory, disk, and network usage helps you:

• Identify bottlenecks before they cause downtime
• Right-size your server plan
• Debug performance issues
• Plan capacity for growth

CPU Monitoring

Quick Check

# Current load average (1, 5, 15 minutes)
uptime
# 10:30:00 up 45 days, load average: 0.85, 1.20, 0.95

# Real-time process viewer
htop

Understanding Load Average

Tip Multiply these thresholds by your CPU core count. A 4-core server is comfortable at load 4.0.

Per-Process CPU Usage

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

# Watch a specific process
pidstat -p $(pgrep nginx) 1

Memory Monitoring

free -h
#               total        used        free      shared  buff/cache   available
# Mem:           3.8Gi       1.2Gi       312Mi       45Mi       2.3Gi       2.3Gi
# Swap:          2.0Gi          0B       2.0Gi

Key metrics:

• available (not free) tells you how much memory applications can use
• Linux uses free memory for disk cache — this is normal and healthy
• If swap used is consistently high, you need more RAM

Disk Monitoring

# Disk space usage
df -h /
# /dev/vda1  50G   12G   36G  25% /

# Find largest directories
du -sh /var/* | sort -rh | head -10

# Disk I/O activity
iostat -x 1 3

Warning If disk usage exceeds 90%, services may fail to write logs, temp files, or database data. Set up alerts before this happens.

Network Monitoring

# Install vnstat for bandwidth tracking
sudo apt install -y vnstat

# Monthly summary
vnstat -m

# Live traffic
vnstat -l

# Connection counts by state
ss -s

Setting Up Simple Alerts

Create a quick monitoring script:

#!/bin/bash
# /opt/monitor/check.sh

DISK_THRESHOLD=85
MEM_THRESHOLD=90

# Check disk
DISK_USAGE=$(df / | awk 'NR==2 {print int($5)}')
if [ "$DISK_USAGE" -gt "$DISK_THRESHOLD" ]; then
    echo "ALERT: Disk usage at ${DISK_USAGE}%" | mail -s "Disk Alert" admin@example.com
fi

# Check memory
MEM_USAGE=$(free | awk '/^Mem:/ {printf("%.0f", $3/$2 * 100)}')
if [ "$MEM_USAGE" -gt "$MEM_THRESHOLD" ]; then
    echo "ALERT: Memory usage at ${MEM_USAGE}%" | mail -s "Memory Alert" admin@example.com
fi

Schedule it with cron:

*/5 * * * * /opt/monitor/check.sh