How Do I Monitor My Server?

Server monitoring helps you detect problems before they become critical. This guide shows you various methods – from simple console commands to professional monitoring tools. This way you always keep an eye on CPU, RAM, disk space and network.

Note: Detailed subpages on individual tools can be found in the left navigation.

Why monitoring is important

• Detect problems early before users complain
• Identify bottlenecks and upgrade selectively
• Track down crashes and their causes
• Recognize long-term trends (e.g. increasing load due to more visitors)

1. Real-time monitoring via console

htop – Interactive process monitor

htop

htop displays CPU, RAM and swap in colored bars. You can sort, filter and kill processes at the press of a key. The most important indicators:

• CPU bars at the top: One bar per core. Full load on one core = single-thread problem
• RAM bar: Green = used, Blue = buffers, Yellow = cache. Only when green is full does it become tight
• Load Average: Three numbers (1, 5, 15 minutes). Higher than core count = overload
• Swap: Visible in the upper area. Constant swap usage = RAM problem

Glances – Everything at a glance

# Installation
apt install glances   # Debian/Ubuntu
pip install glances   # Alternatively via pip

# Start
glances

Glances combines CPU, RAM, I/O, network and disks in a single view. Less interactive than htop, but clearer for a quick overview. With glances -w you start a web server on port 61208 for browser access.

2. Monitoring disk space

df – Check partitions

df -h

Shows all partitions with size, used and available space. Watch for values above 90% – then it becomes critical.

ncdu – Interactive disk space analyzer

apt install ncdu
ncdu /

ncdu shows folder sizes in a navigable tree view. Perfect for finding space hogs. Navigate with arrow keys, delete with d.

Automatic alert via script

#!/bin/bash
# Disk space alert via email
THRESHOLD=90
df -h | awk '{if (NR!=1) {print $5 " " $6}}' | while read output; do
    usep=$(echo $output | awk '{print $1}' | cut -d'%' -f1)
    partition=$(echo $output | awk '{print $2}')
    if [ $usep -ge $THRESHOLD ]; then
        echo "Warning: Partition $partition is $usep% full" | mail -s "Disk Space Warning" [email protected]
    fi
done

Set up as a daily cronjob:

0 8 * * * /path/to/script.sh

3. Network monitoring

iftop – Real-time bandwidth usage

apt install iftop
iftop -i eth0

Shows which connections are using how much bandwidth. Sender on the left, receiver on the right. Useful to see if a single client is flooding the server or a backup is blocking the line.

nload – Simple bandwidth monitor

apt install nload
nload eth0

Shows incoming and outgoing traffic as graphs with average and peak values. Fewer details than iftop, but easier to interpret.

vnstat – Traffic statistics over time

apt install vnstat
vnstat -d   # Daily statistics
vnstat -m   # Monthly statistics
vnstat -h   # Hourly statistics

vnstat runs as a daemon and records traffic data continuously. Ideal for long-term analysis – unlike iftop, which only shows the current moment.

4. Long-term monitoring and notifications

Netdata – Professional monitoring with web interface

# Installation (one command)
bash