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Configure Nagios Core for Log Monitoring

No matter how well we set up our infrastructure, eventually something will go wrong that needs to be fixed. When that happens, the first step is to check the logs for errors and warnings. In this hands-on lab, we will create a Nagios service that monitors the logs for errors and warnings using the `check_log` plugin.

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Path Info

Level

Intermediate

Duration

1h 0m

Last updated

Aug 30, 2025

Challenge

Define Two Command Objects that Check the Logs /var/log/messages for Errors and Warnings in /usr/local/nagios/etc/objects/commands.cfg

Add the following text to the commands.cfg file:

define command {

        command_name    check_log_error
        command_line    /usr/local/nagios/libexec/check_log -F /var/log/messages -O /home/nagios/check_log.error -q "error"

}

define command {

        command_name    check_log_warning
        command_line    /usr/local/nagios/libexec/check_log -F /var/log/messages -O /home/nagios/check_log.warning -q "warning"

}

Challenge

Define Two Services that Use the Commands

Add the following text to the localhost.cfg file:

define service {

        use                     local-service
        host_name               localhost
        service_description     Check Log Error
        check_command           check_log_error

}

define service {

        use                     local-service
        host_name               localhost
        service_description     Check Log Warnings
        check_command           check_log_warning

}

Challenge

Give the `nagios` User Read Permissions for `/var/log/messages`
1. Run the following command:
```
sudo setfacl -R -m u:nagios:r-- /var/log/messages
```
Challenge

Restart and Log In to the Nagios Server
1. Restart the Nagios server.
```
sudo systemctl restart nagios
```
1. Navigate to http://NAGIOS_SERVER_IP/nagios, and log in with the following credentials:
  - User Name: nagiosadmin
  - Password: BlaBla321
2. Navigate to Services.
3. Reschedule the checks for the two services to run 10-20 seconds from the current server time.
4. Verify that there are no errors under Status Information.

Author

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Configure Nagios Core for Log Monitoring

Path Info

Table of Contents

Define Two Command Objects that Check the Logs **/var/log/messages** for Errors and Warnings in **/usr/local/nagios/etc/objects/commands.cfg**