Installation of NRPE daemon with its Prerequisites
In this section, you are going to install NRPE Daemon with its required Nagios plug-ins for monitoring of the web server using NRPE (Nagios Remote Plugin Executor). It is to be remembered that the NRPE daemon is a plug-in used by the remote hosts (or servers) and hence, it should be understood that the NRPE daemon will be installed on the remote host.
Log into your web server and create a Nagios user for NRPE agent using the below command.
sudo useradd nagios
Installation of Nagios Plug-ins
Step 1: Updating the Packages
Now, you need to install the NRPE which requires the development libraries as similar to the check_nrpe installation section.
To update the package sources and install NRPE along with its libraries, use the command:
sudo apt update sudo apt install autoconf gcc libmcrypt-dev make libssl-dev wget dc build-essential gettext
Step 2: Downloading Nagios Plug-ins
NRPE requires the Nagios plug-ins to work properly. Install the Nagios plug-ins from the source and make sure you installed the same plug-ins which you once used to install the Nagios server.
To download the latest stable version of the plug-in bundle, go to nagios-plugins.org/
Download the Nagios plug-ins using the curl command.
curl -L -O https://nagios-plugins.org/download/nagios-plugins-2.2.1.tar.gz
Step 3: Configuring Plug-ins
Extract the Nagios plug-in which you downloaded in the previous step.
tar zxf nagios-plugins-2.2.1.tar.gz
Enter the extracted directory using the below command,
cd nagios-plugins-2.2.1
Next, configure the Nagios plug-in.
./configure
Post configuring the Nagios plug-in, it’s time to install and build the plug-ins.
sudo make sudo make install
Installation of NRPE daemon
Step 1: Installing NRPE
Install the latest stable version of NRPE daemon using the curl command.
For the latest stable version of NRPE daemon, https://github.com/NagiosEnterprises/nrpe/releases.
curl -L -O https://github.com/NagiosEnterprises/nrpe/releases/download/nrpe-3.2.1/nrpe-3.2.1.tar.gz
Extract the NRPE downloaded file.
tar zxf nrpe-3.2.1.tar.gz
Enter the extracted directory using the below command,
cd nrpe-3.2.1
Step 2: Configuring NRPE
Configure the NRPE using the command:
./configure
Next, build and install NRPE and its startup script using the following commands:
sudo make nrpe sudo make install-daemon sudo make install-config sudo make install-init
Next, check the disk usage and file system to update the Nagios configuration file, using the below command,
df -h /
Post which, you will see an output like below,
Output Filesystem Size Used Avail Use% Mounted on /dev/vda1 25G 1.4G 23G 6% /
Now start the NRPE configuration using the following configuration file,
/usr/local/nagios/etc/nrpe.cfg
Open the NRPE configuration file using the below command,
sudo nano /usr/local/nagios/etc/nrpe.cfg
Now, you need to find the following directives in nrpe.cfg file.
server_Address allowed_hosts command[check_hda1]
Note:
- Server_Address: You need to set the IP address of your web server you wish to monitor.
- Allowed_Host: Here, add your IP address of the Nagios server.
- Command[check_hda1]: Check the disk
Now, you need to change the filesystem type which you observed in the above sections using the df -h command.
Locate those lines and update the corresponding values.
… server_address=webserver_ip ... allowed_hosts=127.0.0.1,::1,your_nagios_server_private_ip ... command[check_vda1]=/usr/local/nagios/libexec/check_disk -w 20% -c 10% -p /dev/vda1 …
Note: Since the nrpe.cfg file contains lot of attributes, it is better to arrange the above directories as per the ease of identification, to say, at a single place in the file.
Step 3: Restarting NRPE
Once you complete doing the above changes, restart the NRPE service using below command,
sudo systemctl start nrpe.service
To verify the NRPE service, use the command:
sudo systemctl status nrpe.service
For which you’ll get an output like below,
Output ... Aug 01 06:28:31 client systemd[1]: Started Nagios Remote Plugin Executor. Aug 01 06:28:31 client nrpe[8021]: Starting up daemon Aug 01 06:28:31 client nrpe[8021]: Server listening on 0.0.0.0 port 5666. Aug 01 06:28:31 client nrpe[8021]: Server listening on :: port 5666. Aug 01 06:28:31 client nrpe[8021]: Listening for connections on port 5666 Aug 01 06:28:31 client nrpe[8021]: Allowing connections from: 127.0.0.1,::1,192.168.2.17
Step 4: Enabling Firewall
To ensure a secure connection, you need to use UFW. For that, you need to allow the NRPE service port number in the firewall. The port number of NRPE is 5666.
sudo ufw allow 5666/tcp
Note: In case, if you want to monitor more hosts, follow the above nrpe.cfg file and create multiple files using those directories. After the successful configuration of NRPE, you need to add the same host details in the Nagios server before you check to access the Nagios web interface.
Step 5: Verifying the Connection Between the Servers
Now, you need to confirm whether the Nagios server and web server do possess the communication. To confirm, make sure you logged into Nagios server,
/usr/local/nagios/libexec/check_nrpe -H webserver_ip
You’ll see the following output:
Output NRPE v3.2.1
Monitoring Configuration with Nagios Server
Step 1: Creating Files
Here, you need to define the host and service details for the host which you going to monitor.
You need to create a separate file for each host and eventually add the host details on the Nagios web interface.
Create a separate file for each of the hosts in the following directory.
cd /usr/local/nagios/etc/servers/
Next, create a new file using your remote server’s domain name.
sudo nano /usr/local/nagios/etc/servers/remote_host_name.cfg
Step 2: Defining Hosts
After creating the file, add and define the host and service details for your remote host, using the remote_host_name.cfg file.
define host {
use linux-server
host_name remote_host_name
alias My client server
address remote_host_ip_address
max_check_attempts 5
check_period 24x7
notification_interval 30
notification_period 24x7
}
In this code, you need to update the values of host_name, alias and address.
host_name is the domain name of your remote server which you going to monitor,
alias is the name for identification purposes and finally,
address is the IP address of your remote server.
Step 3: Adding Additional Services
Here, add the following services such as Load Average, Disk Usage, CPU Load, Total Processes and Current Users in your remote_host_name.cfg file.
Add the services after your Host Section using the below file,
sudo nano /usr/local/nagios/etc/servers/remote_host_name.cfg
#Host Section
define host {
use linux-server
host_name remote_host_name
alias My client server
address remote_host_ip_address
max_check_attempts 5
check_period 24x7
notification_interval 30
notification_period 24x7
}
#Add the Load Average service
define service {
use generic-service
host_name remote_host_name
service_description Load average
check_command check_nrpe!check_load
}
#Add the Disk Usage service
define service {
use generic-service
host_name remote_host_name
service_description /dev/vda1 free space
check_command check_nrpe!check_vda1
}
#Add the CPU Load service
define service {
use generic-service
host_name remote_host_name
service_description CPU Load
check_command check_nrpe!check_load
}
#Add the Total Process service
define service {
use generic-service
host_name remote_host_name
service_description Total Processes
check_command check_nrpe!check_total_procs
}
#Add the Current Users service
define service {
use generic-service
host_name remote_host_name
service_description Current Users
check_command check_nrpe!check_users
}
Step 4: Testing the Nagios Host
After adding the above services, you need to restart the Nagios service using the following command,
sudo systemctl restart nagios
Next, go to the Nagios web interface and click ‘Hosts’ presents at the left-side panel of your Nagios dashboard.
Post which, you will able to see the host and other services which you are already included in the previous sections.
