1. Let’s assume we have the following configurations:
Nagios Host: Hostname: monitor IP: 172.20.10.217 OS: Linux/Debian/Ubuntu Example Server: Hostname: server1 IP: 172.20.10.218 OS: Linux/Debian/Ubuntu
2. Install Nagios in both servers
monitor:~# apt-get install nagios3 nagios-plugins nagios-nrpe-plugin server1:~# apt-get install nagios-nrpe-server nagios-plugins
In the process of installing you get asked for samba workgroup and WINS Settings just let these set on default.
3. Putting up a basic nagios configuration on the monitoring host
To get access to the Nagios Configuration Page we have to set the password for the nagiosadmin user:
monitor:~# htpasswd -c /etc/nagios3/htpasswd.users nagiosadmin
After this you should be able to login to: http://172.20.10.217/nagios3/ with the username nagiosadmin and the password you just set before.
If you go to the service detail site you will see that Nagios provides already a basic configuration for the localhost.
4. Install a webserver on the sample server1
server1:~# apt-get install apache2
5. Create a new config file on the nagios host
monitor:~# nano /etc/nagios3/conf.d/server1_nagios2.cfg define host{ use generic-host host_name server1 alias server1 address 172.20.10.218 } define service{ use generic-service host_name server1 service_description HTTP-Server check_command check_http }
Restart the nagios service with:
monitor:~# /etc/init.d/nagios3 restart
The ‘use’ variable in every object here indicates which template is used. The generic-host object can be found in the file /etc/nagios3/generic-host_nagios2.cfg, while the generic-service is determined in the file /etc/nagios3/generic-service_nagios2.cfg.
You should now be able to see the server1 and http service on the Service Detail Site of Nagios.
6. Prepare nrpe client on server1 to submit more data to nagios
We have to change the nrpe config of the server we want to overwatch, first change the line for the allowed host (line 79 by default):
server1:~# nano /etc/nagios/nrpe.cfg
From
allowed_hosts=127.0.0.1
to
allowed_hosts=172.20.10.217
Restart the nrpe service on server1:
server1:~# /etc/init.d/nagios-nrpe-server restart
Check the nrpe-service by hand before we continue to change the config. We do this from our Nagios host.
monitor:~# cd /usr/lib/nagios/plugins/ monitor:/usr/lib/nagios/plugins# ./check_nrpe -H 172.20.10.218 -c check_users
The output should be something like this:
USERS OK - 2 users currently logged in |users=2;5;10;0
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