Monit: Home server system load monitoring (CPU, RAM, Swap)

System load monitoring with Monit allows you to keep a check on your home server or web server. Monit is an automatic monitoring, maintenance, and repair utility for Unix systems. If the resource usage is high Monit will send you an email alert. You can then examine and resolve any issues. In this Monit tutorial, I will show you how to monitor server load with Monit. By server load I mean the load on the CPU, memory usage, swap partition usage, and system load in general. I am assuming that you have already installed and configured Monit following my previous guide.

Monitor your home server with Monit:

System Load Monitoring with Monit

It is required that you have a working Monit instance with a proper /etc/monit/monitrc file. Monit configurations for various services are loaded from /etc/monit/conf.d folder. To monitor server load with Monit, create a Monit configuration file using the following command:

sudo /etc/monit/conf.d/systemload

Copy the following contents to it, save, and exit (press Ctrl X, press Y, and press ENTER).

# could be IP, hostname, or localhost
check System
    if loadavg (1min) > 4 then alert
    if loadavg (5min) > 2 then alert
    if memory usage > 75% then alert
    if swap usage > 25% then alert
    if cpu usage (user) > 80% then alert
    if cpu usage (system) > 30% then alert
    if cpu usage (wait) > 20% then alert

This code will make Monit send you an email alert when one of the above conditions (eg. average load is >4 for at least 1 min or when more than 75% RAM is full) are met. You can customize the above rules as you please. Below is an example email alert sent by Monit along with a description of what condition caused the alert.

Monit System Monitoring Email Alert
Monit System Monitoring Email Alert

The conditions I have listed are good for general purposes. But if you have a very low power system or a low RAM system then that may trigger alerts more often as it is quite easy for the resource usage to be high. The reverse is also true. In such cases, I would set load time length or load value higher or lower.

Test and Reload Monit

Once you make any changes you have to test Monit configuration:

sudo monit -t

You should see the following message: Control File Syntax OK. Then, check to see if Monit is already running using the following command:

sudo /etc/init.d/monit status

If Monit is running, reload Monit configurations using the following command:

sudo /etc/init.d/monit reload

If Monit is not running, then start it using sudo monit command instead. The whole sequence of commands for testing and reloading Monit is shown in the picture below.

Monit Test and Reload
Monit Test and Reload

Now, fire up your web browser and visit one of the following URLs depending on how your Monit is configured (be sure to use the correct port number):

  • http://localhost:2812
  • http://IPADDRESS:2812 (local network IP)
  • (if you have domain name pointing to your server)

You should see the system status, load, CPU load, Memory Load, and Swap load as shown in the picture below.

System Load Monitoring with Monit
System Load Monitoring with Monit

That is it for system load monitoring with Monit. As you can see Monit allows for automatic server monitoring, which can be a big help for system administrators. Monit Wiki page has several examples. More home server specific Monit examples to follow, so keep checking back.

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