Using SSH to Check Services

1. On the Nagios server, become the nagios user.

sudo su nagios

2. Generate SSH keys for the nagios user.

ssh-keygen

1. Run the following command from the Nagios server:

vim /home/nagios/.ssh/id_rsa.pub

1. Select the SSH key, and copy it to your clipboard.
2. On the client, open the authorized_keys file.

sudo vim /home/cloud_user/.ssh/authorized_keys

1. Paste the SSH key at the end of the file, then save and exit.

1. From the Nagios server, run the following command:

ssh cloud_user@CLIENT_IP

1. Run the following command from the Nagios server:

sudo -i scp /usr/local/nagios/libexec/check_disk cloud_user@CLIENT_IP:/home/cloud_user/

1. From the Nagios server, change to the /usr/local/nagios/etc/objects/ directory.

cd /usr/local/nagios/etc/objects/

1. Open the commands.cfg file.

sudo vim commands.cfg

1. Add the following to the file:

define command {

       command_name    ssh_check_disk
       command_line    /usr/local/nagios/libexec/check_by_ssh -H $HOSTADDRESS$ -i /home/nagios/.ssh/id_rsa -l cloud_user -C "/home/cloud_user/check_disk -w 10% -c 5% -p /"
}

1. Create a new file named linux-server.cfg in the /usr/local/nagios/etc/objects/ directory.

sudo touch /usr/local/nagios/etc/objects/linux-server.cfg

1. Open the file.

sudo vim /usr/local/nagios/etc/objects/linux-server.cfg

1. Add the following to the file:

define host {

       use                     linux-server
       host_name               Linux Server
       alias                   linuxSrv
       address                 CLIENT_IP
 
 }

 define hostgroup {

       hostgroup_name          my-linux-servers
       alias                   Linux Servers
       members                 Linux Server

 }

 define service {

       use                     generic-service
       host_name               Linux Server
       service_description     Check DISK
       check_command           ssh_check_disk

 }

1. Run the following command:

sudo vim /usr/local/nagios/etc/nagios.cfg

1. Add the following to the file:

Definitions for monitoring a network printer
cfg_file=/usr/local/nagios/etc/objects/linux-server.cfg

1. Save and exit the file.
2. Run a preflight check.

sudo /usr/local/nagios/bin/nagios -v /usr/local/nagios/etc/nagios.cfg

1. Restart Nagios.

sudo systemctl restart nagios

1. Check the status of Nagios.

sudo systemctl status nagios

1. In a private browser tab, navigate to http://NAGIOS_SERVER_IP/nagios.
2. Log in with the following credentials:
   • User Name: nagiosadmin
   • Password: BlaBla321
3. Click Services > Check DISK.
4. Under Service Commands, click Re-schedule the next check of this service.
5. Next to Check Time, enter a time approximately 10-20 seconds from now (you can check the current time using the date command in your terminal window).
6. Click Commit, then Done.
7. Click Services in the left sidebar.
8. Verify that there are no errors for the Check DISK service under Status Information.