Install Nagios Core on Managed Server

Introduction

In this tutorial we will learn how to install a rootless Nagios Core monitoring system with a basic configuration on a Managed Server. Before we can run Nagios we need to compile our own versions of Apache and PHP since we can't use the preinstalled managed versions to get it to work. After the installation of Nagios and previously mentioned dependencies a few small adjustments in its configurations are necessary.

Prerequisites

Managed Server with enabled SSH access
Hetzner Development Package (hos-dev) -> please ask the support

Step 1 - Install Nagios Core and dependencies

First we need to download and and compile various sources.

Before we start, create a directory for the sources to keep the home directory clean.

cd
mkdir src
cd src

Step 1.1 - Apache HTTP Server source installation

Download and compile the Apache sources.

Always check here for newer stable versions

wget https://apache.org/dist/httpd/httpd-2.4.46.tar.bz2
wget https://apache.org/dist/apr/apr-1.7.0.tar.bz2
wget https://apache.org/dist/apr/apr-util-1.6.1.tar.bz2
tar xjvf httpd-2.4.46.tar.bz2
tar xjvf apr-1.7.0.tar.bz2
tar xjvf apr-util-1.6.1.tar.bz2
cp -r apr-1.7.0 httpd-2.4.46/srclib/apr
cp -r apr-util-1.6.1 httpd-2.4.46/srclib/apr-util
cd httpd-2.4.46
./configure --prefix=/usr/home/holu/nagios --with-included-apr --enable-so
make -j $(($(grep ^cpu\ cores /proc/cpuinfo | uniq | sed s/[^0-9]//g)+1))
make install
cd ..

Step 1.2 - PHP 7.3 source installation

First install the dependency pkg-config and libxml2 using the Custom Software Installer.

software install pkg-config
software install libxml2

Next download and compile the PHP 7.3 sources.

Always check here for newer stable versions
At the moment Nagios only works properly with PHP 7.3

wget https://www.php.net/distributions/php-7.3.25.tar.xz
tar xJvf php-7.3.25.tar.xz
cd php-7.3.25
./configure --prefix=/usr/home/holu/nagios --with-apxs2=/usr/home/holu/nagios/bin/apxs --with-config-file-path=/usr/home/holu/nagios/conf/
make -j $(($(grep ^cpu\ cores /proc/cpuinfo | uniq | sed s/[^0-9]//g)+1))
make install
cp php.ini-development /usr/home/holu/nagios/conf/php.ini
cd ..

Step 1.3 - Nagios Core source installation

Everything is fine to compile Nagios now.

Always check here for newer stable versions

wget https://downloads.sourceforge.net/project/nagios/nagios-4.x/nagios-4.4.6/nagios-4.4.6.tar.gz
tar xzvf nagios-4.4.6.tar.gz
cd nagios-4.4.6
./configure --prefix=/usr/home/holu/nagios/nagios --with-cgiurl=/nagios/cgi-bin --with-htmurl=/nagios/ --with-nagios-user=holu --with-nagios-group=holu --with-command-group=holu --with-httpd-conf=/usr/home/holu/nagios/conf
make all -j $(($(grep ^cpu\ cores /proc/cpuinfo | uniq | sed s/[^0-9]//g)+1))
make install
make install-commandmode
make install-config
make install-webconf
cp -r contrib/eventhandlers/ /usr/home/holu/nagios/nagios/libexec/
cd ..

Step 1.4 - Monitoring Plugins source installation

Finally compile the Monitoring Plugins.

Always check here for newer stable versions

wget https://www.monitoring-plugins.org/download/monitoring-plugins-2.3.tar.gz
tar xzvf monitoring-plugins-2.3.tar.gz
cd monitoring-plugins-2.3
./configure --prefix=/usr/home/holu/nagios/nagios --with-nagios-user=holu --with-nagios-group=holu
make -j $(($(grep ^cpu\ cores /proc/cpuinfo | uniq | sed s/[^0-9]//g)+1))
make install

Step 2 - Basic configuration of Apache

In this step we will edit the configuration of Apache.

The main Apache configuration file can be found under

/usr/home/holu/nagios/conf/httpd.conf

Step 2.1 - Change the default Apache Port

Open the httpd.conf, search for Listen 80 and replace the Port with any free Port > 1024 (In this tutorial we use 8080).

Listen 8080

Step 2.2 - Enable PHP and CGI

Search and uncomment the line below to load the cgid module.

LoadModule cgid_module modules/mod_cgid.so

Extend the DirectoryIndex directive with index.php.

#
# DirectoryIndex: sets the file that Apache will serve if a directory
# is requested.
#
<IfModule dir_module>
    DirectoryIndex index.html index.php
</IfModule>

Add the following directive to the end of the file.

<FilesMatch \.php$>
    SetHandler application/x-httpd-php
</FilesMatch>

Step 2.3 - Enable the Nagios webconfig

The following include enables the Nagios webconfig. Add it to the end of the file.

Include conf/nagios.conf

Step 3 - Basic configuration of Nagios

In this step we will edit the Nagios webconfig for Apache, add an email contact for notifications and set a password for the BasicAuth which protects the WebGUI.

The Nagios webconfig file can be found under

/usr/home/holu/nagios/conf/nagios.conf

The Nagios contact definitions file can be found under

/usr/home/holu/nagios/nagios/etc/objects/contacts.cfg

Step 3.1 - Fix the Nagios webconfig

Unfortunately the default Alias directive in the Nagios webconfig does not work with Apache, but as solution it can be replaced with a symbolic link.

Comment out the Alias directive and change the Directory directive for "/usr/home/holu/nagios/nagios/share" like the content below.

#Alias /nagios/ "/usr/home/holu/nagios/nagios/share"

<Directory "/usr/home/holu/nagios/htdocs/nagios">

Add a symbolic link

ln -s /usr/home/holu/nagios/nagios/share /usr/home/holu/nagios/htdocs/nagios

Step 3.2 - Add a valid email address to contact definition

To receive email notifications and avoid undeliverable emails from your Nagios server you should replace the default address holu@localhost with a valid address.

###############################################################################
#
# CONTACTS
#
###############################################################################

# Just one contact defined by default - the Nagios admin (that's you)
# This contact definition inherits a lot of default values from the
# 'generic-contact' template which is defined elsewhere.

define contact {

    contact_name            nagiosadmin             ; Short name of user
    use                     generic-contact         ; Inherit default values from generic-contact template (defined above)
    alias                   Nagios Admin            ; Full name of user
    email                   monitor@example.com ; <<***** CHANGE THIS TO YOUR EMAIL ADDRESS ******
}

Step 3.3 - Set a password for the WebGUI

Create a password database file for Apache BasicAuth. The user should always be "nagiosadmin".

htpasswd -c /usr/home/holu/nagios/nagios/etc/htpasswd.users nagiosadmin

Step 4 - Post installation

Step 4.1 - The first start

Start the services

/usr/home/holu/nagios/bin/apachectl start
/usr/home/holu/nagios/nagios/bin/nagios /usr/home/holu/nagios/nagios/etc/nagios.cfg &

If you want to run the processes as permanent services, please consider to ask the support for process releases of "nagios" and "httpd".

Step 4.2 - Choose a way to access

The easiest way to access is a SSH tunnel from a local workstation.

ssh holu@dediX.your-server.de -p222 -L 8080:localhost:8080

Alternatively you can add a proxy rewrite rule to the .htaccess of the managed Apache.

RewriteEngine on
RewriteRule   ^(.*)  http://localhost:8080/$1 [P]

You can also add an incoming firewall rule to Port 8080/tcp in konsoleH. I strongly recommend to release only trusted IP adresses if you want to do it this way.

Conclusion

Now you have a solution to start your rootless Nagios Core monitoring system on a Managed Server. Please read the following documentation for further information.