Using SSH to Check Services

You need to connect to and perform a check on a client machine from the Nagios server. Due to your university’s firewall rules (port 5666 is not allowed for NRPE), you will need to use SSH. In this hands-on lab, we will configure an SSH check on a client and the Nagios server.

Learning Objectives

Successfully complete this lab by achieving the following learning objectives:

Generate SSH Keys for the nagios User

On the Nagios server, become the nagios user.
```
sudo su nagios
```
Generate SSH keys for the nagios user.
```
ssh-keygen
```

Copy the Public Key from the Nagios Server to the Client

Run the following command from the Nagios server:
```
vim /home/nagios/.ssh/id_rsa.pub
```
Select the SSH key, and copy it to your clipboard.

On the client, open the authorized_keys file.

sudo vim /home/cloud_user/.ssh/authorized_keys

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

Test the SSH Connection

From the Nagios server, run the following command:
```
ssh cloud_user@CLIENT_IP
```

Copy the check_disk Binaries from the Nagios Server to the Client

Run the following command from the Nagios server:

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

Define an SSH Check Command Object on the Nagios Server

From the Nagios server, change to the /usr/local/nagios/etc/objects/ directory.
```
cd /usr/local/nagios/etc/objects/
```
Open the commands.cfg file.
```
sudo vim commands.cfg
```

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 /"
}

Create the Host, Host Group, and Service Object Definitions

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
```

Open the file.

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

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

}

Inform Nagios of the New File, Perform a Preflight Check, and Restart Nagios

Run the following command:

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

Add the following to the file:

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

Save and exit the file.

Run a preflight check.

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

Restart Nagios.
```
sudo systemctl restart nagios
```
Check the status of Nagios.
```
sudo systemctl status nagios
```

Log In to the Nagios Web Interface and Reschedule a Check for the Check DISK Service

In a private browser tab, navigate to http://NAGIOS_SERVER_IP/nagios.
Log in with the following credentials:
- User Name: nagiosadmin
- Password: BlaBla321
Click Services > Check DISK.
Under Service Commands, click Re-schedule the next check of this service.
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).
Click Commit, then Done.
Click Services in the left sidebar.
Verify that there are no errors for the Check DISK service under Status Information.

What are Hands-on Labs

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Using SSH to Check Services

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Learning Objectives

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