First, install the required packages:
sudo yum install gcc glibc glibc-common gd gd-devel make net-snmp openssl-devel xinetd unzip
We must create a user and group that will run the Nagios process. Create a "nagios" user and "nagcmd" group, then add the user to the group with these commands:
sudo useradd nagios sudo groupadd nagcmd sudo usermod -a -G nagcmd nagios
Let's install Nagios now.
Download the source code for the latest stable release of Nagios Core. Go to the Nagios downloads page, and click the Skip to download link below the form. Copy the link address for the latest stable release so you can download it to your Nagios server.
At the time of this writing, the latest stable release is Nagios 4.1.1. Download it to your home directory with curl:
cd ~ curl -L -O https://assets.nagios.com/downloads/nagioscore/releases/nagios-4.1.1.tar.gz
Extract the Nagios archive with this command:
tar xvf nagios-*.tar.gz
Then change to the extracted directory:
cd nagios-*
Before building Nagios, we must configure it with this command:
./configure --with-nagios-group=nagios --with-command-group=nagcmd --with-mail=/usr/bin/sendmail --with-httpd-conf=/etc/httpd/conf.d
Now compile Nagios with this command:
make all
Now we can run these make commands to install Nagios, init scripts, and sample configuration files:
sudo make install sudo make install-initsudo make install-commandmode sudo make install-config sudo make install-webconf
In order to issue external commands via the web interface to Nagios, we must add the web server user, apache, to the nagcmd group:
apache
nagcmd
Find the latest release of Nagios Plugins here: Nagios Plugins Download. Copy the link address for the latest version, and copy the link address so you can download it to your Nagios server.
At the time of this writing, the latest version is Nagios Plugins 2.1.1. Download it to your home directory with curl:
cd ~ curl -L -O http://nagios-plugins.org/download/nagios-plugins-2.1.1.tar.gz
Extract Nagios Plugins archive with this command:
tar xvf nagios-plugins-*.tar.gz
cd nagios-plugins-*
Before building Nagios Plugins, we must configure it. Use this command:
./configure --with-nagios-user=nagios --with-nagios-group=nagios --with-openssl
Now compile Nagios Plugins with this command:
make
Then install it with this command:
sudo make install
Find the source code for the latest stable release of NRPE at the NRPE downloads page. Download the latest version to your Nagios server.
At the time of this writing, the latest release is 2.15. Download it to your home directory with curl:
Extract the NRPE archive with this command:
Configure NRPE with these commands:
echo >> /etc/services
echo '# Nagios services' >> /etc/services
echo 'nrpe 5666/tcp' >> /etc/services
Now build and install NRPE and its xinetd startup script with these commands:
Open the xinetd startup script in an editor:
service nrpe{ flags = REUSE socket_type = stream port = 5666 wait = no user = nagios group = nagios server = /usr/sbin/nrpe server_args = -c /usr/local/nagios/etc/nrpe.cfg --inetd log_on_failure += USERID disable = no only_from = 127.0.0.1}
Modify the only_from line by adding the private IP address of the your Nagios server to the end (substitute in the actual IP address of your server):
only_from
only_from = 127.0.0.1 10.132.224.168
Save and exit. Only the Nagios server will be allowed to communicate with NRPE.
Restart the xinetd service to start NRPE:
Now that Nagios 4 is installed, we need to configure it.
# sed -i '/^allowed_hosts=/s/$/,10.25.5.2/' /usr/local/nagios/etc/nrpe.cfg# sed -i 's/^dont_blame_nrpe=.*/dont_blame_nrpe=1/g' /usr/local/nagios/etc/nrpe.cfg
Now check that NRPE is listening and responding to requests.
# /usr/local/nagios/libexec/check_nrpe -H 127.0.0.1
You should see the output similar to the following:
NRPE v3.2.1
# systemctl start nrpe.service# systemctl stop nrpe.service# systemctl restart nrpe.service# systemctl status nrpe.service
Now let's perform the initial Nagios configuration. You only need to perform this section once, on your Nagios server.
Open the main Nagios configuration file in your favorite text editor. We'll use vi to edit the file:
sudo vi /usr/local/nagios/etc/nagios.cfg
Now find an uncomment this line by deleting the #:
#
#cfg_dir=/usr/local/nagios/etc/servers
Save and exit.
Now create the directory that will store the configuration file for each server that you will monitor:
sudo mkdir /usr/local/nagios/etc/servers
Open the Nagios contacts configuration in your favorite text editor. We'll use vi to edit the file:
sudo vi /usr/local/nagios/etc/objects/contacts.cfg
Find the email directive, and replace its value (the highlighted part) with your own email address:
email nagios@localhost ; <<***** CHANGE THIS TO YOUR EMAIL ADDRESS ******
Let's add a new command to our Nagios configuration:
Add the following to the end of the file:
define command{ command_name check_nrpe command_line $USER1$/check_nrpe -H $HOSTADDRESS$ -c $ARG1$ }
Save and exit. This allows you to use the check_nrpe command in your Nagios service definitions.
check_nrpe
Use htpasswd to create an admin user, called "nagiosadmin", that can access the Nagios web interface:
sudo htpasswd -c /usr/local/nagios/etc/htpasswd.users nagiosadmin
Enter a password at the prompt. Remember this login, as you will need it to access the Nagios web interface.
Note: If you create a user that is not named "nagiosadmin", you will need to edit /usr/local/nagios/etc/cgi.cfg and change all the "nagiosadmin" references to the user you created.
/usr/local/nagios/etc/cgi.cfg
Nagios is ready to be started. Let's do that, and restart Apache:
sudo systemctl daemon-reload sudo systemctl start nagios.service sudo systemctl restart httpd.service
To enable Nagios to start on server boot, run this command:
sudo chkconfig nagios on
If you want to restrict the IP addresses that can access the Nagios web interface, you will want to edit the Apache configuration file:
sudo vi /etc/httpd/conf.d/nagios.conf
Find and comment the following two lines by adding # symbols in front of them:
Order allow,deny Allow from all
Then uncomment the following lines, by deleting the # symbols, and add the IP addresses or ranges (space delimited) that you want to allow to in the Allow from line:
Allow from
# Order deny,allow # Deny from all # Allow from 127.0.0.1
As these lines will appear twice in the configuration file, so you will need to perform these steps once more.
Now start Nagios and restart Apache to put the change into effect:
sudo systemctl restart nagios.service sudo systemctl restart httpd.service
Nagios is now running, so let's try and log in.
Open your favorite web browser, and go to your Nagios server (substitute the IP address or hostname for the highlighted part):
http://nagios_server_public_ip/nagios
Because we configured Apache to use htpasswd, you must enter the login credentials that you created earlier. We used "nagiosadmin" as the username:
After authenticating, you will be see the default Nagios home page. Click on the Hosts link, in the left navigation bar, to see which hosts Nagios is monitoring:
As you can see, Nagios is monitoring only "localhost", or itself.
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