Simple monitoring and alerting with Monit on Ubuntu 22.04 LTS

TLDR Guide

On Ubuntu 22.04:

 sudo apt update
 sudo apt install monit -y
 sudo systemctl enable monit --now

Example config:

check filesystem root with path /dev/sda1
    if space usage > 90% for 5 cycles then alert

Mailserver config example using Gmail in /etc/monit/monitrc:

set mailserver smtp.gmail.com port 587
    username "your-username" password "12-digit-app-password"
    using tlsv13
    with timeout 30 seconds

set alert your-username+alerting@gmail.com

Then reload Monit:

 sudo monit reload

Introduction

Monit is a utility to monitor your services, systems, and processes and also can handle alarms as well. Not only that, monit is available on most official upstream repositories. It has a lightweight web user interface that allows you to review the monitored components in a simple visual representation.

So, in this article, I will show you how to install Monit, how to monitor things, and to set the alerting for them as well. This time, I will use a Ubuntu 22.04 VM instance.

Installation Steps

Step 1. Do a repository update and install Monit:

sudo apt update
sudo apt install monit -y

Step 2. Start monit service and enable it

sudo systemctl enable monit --now

Step 3. Open the /etc/monit/monitrc file, then find the following lines and uncomment them to enable the Web UI (specify the SSL cert path if you have one):

set httpd port 2812 and
    use address localhost  
    allow localhost        
    allow admin:monit

Step 4. Reload monit.

sudo monit reload

Step 5. Test it by issuing sudo monit status, it should output something like this:

You can access the Web UI by tunneling port 2812 to any free local port on your PC/Laptop.

Monitoring things

Monit can monitor a variety of things, for instance:

• Monitor websites using HTTP or HTTPS protocol
• Monitor TCP ports
• Monitor remote hosts
• Monitor popular protocols like SMTP, FTP, LDAP, etc.
• Monitor SSL certificates
• Monitor processes
• Monitor files, directories, and disks
• Monitor network interfaces
• Monitor a program’s output
• Etc.

This time, I’ll show an example of how to monitor a remote host and local disk usage.

Monitor a remote host

Step 1. Go to /etc/monit/conf.d and create a new file. The name could be anything, but for example, name it simply “host”

Step 2. Edit the file with the following content:

check host myhost with address IP-ADDRESS
    if failed ping then alert

It basically means that we monitor a host at the specified IP-ADDRESS and if it can’t be pinged then send an alert. Pretty straightforward right?

Step 3. Do a sudo monit reload to allow Monit to reload its configurations without stopping the service.

Step 4. Check the monitoring using sudo monit status myhost

Monitor a local disk

Step 1. Create a new config file in /etc/monit/conf.d and name it a “disk”

Step 2. Fill in the file with the following configuration. You may change the disk to your actual disk path:

check filesystem root with path /dev/sda1
    if space usage > 90% then alert

Step 3. Reload monit: sudo monit reload

Step 4. Verify the monitor: sudo monit status root

Configure email alerting

Step 1. Open /etc/monit/monitrc

Step 2. Add the following lines and adjust the data accordingly

set maileserver your.smtp-server.com port the-port
    username "username" password "password"
    using tls 

set alert alert-recipient@example.com

However, if you only have a public mailing service like Gmail for instance, you can use the following configuration:

set mailserver smtp.gmail.com port 587
    username "username-without-atgmailcom" password "the-password"
    using tls
    with timeout 30 seconds

set alert alert-recipient@example.com

Step 3. Test the alert by simply reloading the Monit. Example email:

You can change the alerting format in the monitrc file, just try to look around at the config.

Additional Notes

For more examples of how to add other monitoring types, please visit Monit’s official documentation here: https://mmonit.com/monit/documentation/monit.html

Conclusion

It’s so easy to install and configure Monit and monitor things with it.

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