How To Install And Configure Monit On Ubuntu 18.04 LTS

Monit is an open-source utility used to supervise the processes and restart the services which are configured for it and have failed. Monit supervises the processes and restarts them on failure detection. This tutorial provides the steps required to install Monit on the popular Linux distribution Ubuntu. It provides all the steps required to install and use Monit on Ubuntu 18.04 LTS. The steps should be similar for other Linux systems and Ubuntu versions.

Official Definition

Monit is a small Open Source utility for managing and monitoring Unix systems. Monit conducts automatic maintenance and repair and can execute meaningful causal actions in error situations.

Install Monit

Use the below-mentioned command to install Monit on Ubuntu.

# Install Monit
sudo apt-get install monit

# Sample output
....
....
Unpacking monit (1:5.25.1-1build1) ...
Setting up monit (1:5.25.1-1build1) ...
Processing triggers for man-db (2.8.3-2ubuntu0.1) ...
Processing triggers for ureadahead (0.100.0-21) ...
Processing triggers for systemd (237-3ubuntu10.29) ...

Important Commands

We can use the below-mentioned commands to enable/disable, stop, start, and restart Monit.

# Enable Monit
sudo systemctl enable monit

# Disable Monit
sudo systemctl disable monit

# Start Monit
sudo systemctl start monit
# OR
sudo service monit start

# Stop Monit
sudo systemctl stop monit
# OR
sudo service monit stop

# Restart Monit
sudo systemctl restart monit
# OR
sudo service monit restart

# Reload Monit
sudo systemctl reload monit
# OR
sudo service monit reload

Configure Monit

We can configure Monit by updating the configuration file /etc/monit/monitrc. I have updated the default configuration of Monit to allow connections from the localhost as shown below.

# Backup config file
sudo cp /etc/monit/monitrc /etc/monit/monitrc.bck

# Update config file - using nano editor
sudo nano /etc/monit/monitrc

# Default config
...
...
## Monit has an embedded HTTP interface which can be used to view status of
## services monitored and manage services from a web interface. The HTTP
## interface is also required if you want to issue Monit commands from the
## command line, such as 'monit status' or 'monit restart service' The reason
## for this is that the Monit client uses the HTTP interface to send these
## commands to a running Monit daemon. See the Monit Wiki if you want to
## enable SSL for the HTTP interface.
#
set httpd port 2812 and
use address localhost # only accept connection from localhost
allow localhost # allow localhost to connect to the server and
# allow admin:monit # require user 'admin' with password 'monit'
...
...

Save and close the editor. Now restart the Monit using the command as mentioned in the previous section.

# Test configuration changes
sudo monit -t

# Output
Control file syntax OK

# Restart Monit
sudo systemctl restart monit

You may also configure Monit to trigger alert emails as shown below. It expects that an email server is already installed on the system. The next section explains how to configure Monit to trigger emails via SMTP.

# Set Alert Email
set alert <email>
# OR
# Set Alert Email only for Security
set alert <email> on { checksum, permission, uid, gid }

# Example
set alert admin@mydomain.com

We can also configure the alerts to be triggered only for specific failed cycles as shown below.

# Set Alert Email for specific cycle
alert <email> with reminder on 5 cycles

Configure SMTP

This section explains how to configure Monit to use the custom email template and trigger the mail using SMTP using Gmail. We can use a similar setup to trigger the emails via any other mail service.

#Mail Template
set mail-format {
  from: <from email>
  subject: Monit Alert - $EVENT
  message: $EVENT Service $SERVICE
                Date:        $DATE
                Action:      $ACTION
                Host:        $HOST
                Description: $DESCRIPTION

           Yours,
           Monit }

# Configure Mail Server
set mailserver smtp.gmail.com port 587 
  username "<email>" password "<password>" 
  using tlsv1 with timeout 30 seconds

# Configure Alert Receiver
set alert <receiver email>

An example of the above-mentioned configuration is as shown below.

#Mail Template
set mail-format {
  from: admin@mydomain.com
  subject: Monit Alert - $EVENT
  message: $EVENT Service $SERVICE
                Date:        $DATE
                Action:      $ACTION
                Host:        $HOST
                Description: $DESCRIPTION

           Yours,
           Monit }

# Configure Mail Server
set mailserver smtp.gmail.com port 587 
  username "admin@mydomain.com" password "adminpwd" 
  using tlsv1 with timeout 30 seconds

# Configure Alert Receiver
set alert notify@mydomain.com

This is how we can configure the email template and SMTP to trigger the alert emails.

Summary

This is how we can install the Monit on Ubuntu. It also provided the commonly used commands to start, stop, or restart the Monit service. The last sections explained the steps required to configure Monit and to trigger the emails via SMTP using the customized template.