Introduction

This guide is intended to provide you with simple instructions on how to install Nagios from source (code) on Ubuntu and have it monitoring your local machine inside of 20 minutes. No advanced installation options are discussed here - just the basics that will work for 95% of users who want to get started.

These instructions should work with most recent vesrions of Ubuntu with minor changes on some versions.

What You‘ll End Up With

If you follow these instructions, here‘s what you‘ll end up with:

• Nagios and the plugins will be installed underneath /usr/local/nagios
• Nagios will be configured to monitor a few aspects of your local system (CPU load, disk usage, etc.)
• The Nagios web interface will be accessible at http://localhost/nagios/

Required Packages

Make sure you‘ve installed the following packages on your Ubuntu installation before continuing.

• Autoconf
• Apache 2
• PHP
• GCC compiler and development libraries
• GD development libraries
• Unzip

You can use apt-get to install these packages by running the following commands:

sudo apt-get install autoconf gcc libc6 build-essential bc gawk dc gettext libmcrypt-dev libssl-dev make unzip apache2 apache2-utils php5 libgd2-xpm-dev

1) Create Account Information

Become the root user.

sudo -s

Create a new nagios user account and give it a password.

/usr/sbin/useradd -m -s /bin/bash nagios
passwd nagios

You will need to also add a nagios group (if it‘s not created by default).

/usr/sbin/groupadd nagios
/usr/sbin/usermod -G nagios nagios

Create a new nagcmd group for allowing external commands to be submitted through the web interface. Add both the nagios user and the apache user to the group.

/usr/sbin/groupadd nagcmd
/usr/sbin/usermod -a -G nagcmd nagios
/usr/sbin/usermod -a -G nagcmd www-data

2) Download Nagios and the Plugins

Create a directory for storing the downloads.

mkdir ~/downloads
cd ~/downloads

Download the source code tarballs of both Nagios Core and the Nagios plugins (visit https://www.nagios.org/download/ for links to the latest versions). These directions were tested with Nagios 4.2.4 and Nagios Plugins 2.1.4.

wget http://prdownloads.sourceforge.net/sourceforge/nagios/nagios-4.2.4.tar.gz
wget http://prdownloads.sourceforge.net/sourceforge/nagiosplug/nagios-plugins-2.2.1.tar.gz

3) Compile and Install Nagios Core

Extract the Nagios Core source code tarball.

cd ~/downloads
tar xzf nagios-4.2.4.tar.gz
cd nagios-4.2.4

Run the Nagios configure script, passing the name of the group you created earlier, and pointing to the correct Apache configuration directory, like so:

./configure --with-command-group=nagcmd --with-httpd-conf=/etc/apache2/sites-enabled

Compile the Nagios Core source code.

make all

Install binaries, init script, sample config files and set permissions on the external command directory.

make install
make install-init
make install-config
make install-commandmode
update-rc.d nagios defaults

Don‘t start Nagios Core yet - there‘s still more that needs to be done...

4) Customize Configuration

Sample configuration files have now been installed in the /usr/local/nagios/etc directory. These sample files should work fine for getting started with Nagios Core. You‘ll need to make just one change before you proceed ...

Edit the /usr/local/nagios/etc/objects/contacts.cfg config file with your favorite editor and change the email address associated with the nagiosadmin contact definition to the address you‘d like to use for receiving alerts.

vi /usr/local/nagios/etc/objects/contacts.cfg

5) Configure the Web Interface

Install the Nagios Core web config file in the Apache conf.d directory.

make install-webconf
a2enmod rewrite
a2enmod cgi

Create a nagiosadmin account for logging into the Nagios Core web interface. Remember the password you assign to this account - you‘ll need it later.

htpasswd -c /usr/local/nagios/etc/htpasswd.users nagiosadmin

Restart Apache to make the new settings take effect.

ufw allow Apache
ufw reload

 Note: Consider implementing the ehanced CGI security measures described here to ensure that your web authentication credentials are not compromised.

6) Compile and Install the Nagios Plugins

Extract the Nagios plugins source code tarball.

cd ~/downloads
tar xzf nagios-plugins-2.2.1.tar.gz
cd nagios-plugins-2.2.1

Compile and install the plugins.

./configure
make
make install

7) Start Nagios Core

Verify the sample Nagios Core configuration files.

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

If there are no errors, start Nagios Core.

systemctl start nagios.service

8) Login to the Web Interface

You should now be able to access the Nagios Core web interface at the URL below. You‘ll be prompted for the username (nagiosadmin) and password you specified earlier.

http://localhost/nagios/

Click on the "Service Detail" navbar link to see details of what‘s being monitored on your local machine. It will take a few minutes for Nagios Core to check all the services associated with your machine, as the checks are spread out over time.

9) Other Modifications

If you want to receive email notifications for Nagios Core alerts, you need to install the mailx (Postfix) package.

sudo apt-get install mailx
sudo apt-get install postfix

You‘ll have to edit the Nagios Core email notification commands found in /usr/local/nagios/etc/objects/commands.cfg and change any ‘/bin/mail‘ references to ‘/usr/bin/mail‘. Once you do that you‘ll need to restart Nagios Core to make the configuration changes live.

sudo systemctl restart nagios.service

Configuring email notifications is outside the scope of this documentation. Refer to your system documentation, search the web, or look to the Nagios Support Portal or Nagios Community Wiki for specific instructions on configuring your Ubuntu system to send email messages to external addresses.

10) You‘re Done

Congratulations! You sucessfully installed Nagios Core. Your journey into monitoring is just beginning. You‘ll no doubt want to monitor more than just your local machine, so check out the following docs ...

• Monitoring Windows machines
• Monitoring Linux/Unix machines
• Monitoring Netware servers
• Monitoring routers/switches
• Monitoring publicly available services (HTTP, FTP, SSH, etc.)