Important: Installing and configuring Nagios is rather involved. You can't just compile the binaries, run the program and sit back. There's a lot to setup before you can actually start monitoring anything. Relax, take your time and read all the documentation - you're going to need it. Okay, let's get started...
You'll need to have root access to install Nagios as described in this documentation, as you'll be creating users and group, modifying your web server config files, etc. Either login as root before you begin or use the su command to change to the root user from another account.
Getting The Latest Version
You can download the latest version of Nagios from http://www.nagios.org/download.
Unpacking The Distribution
To unpack the Nagios distribution, use the following command:
tar xzf nagios-version.tar.gz
When you have finished executing these commands, you should find a nagios-version directory that has been created in your current directory. Inside that directory you will find all the files that comprise the core Nagios distribution.
Create Nagios User/Group
You're probably going to want to run Nagios under a normal user account, so add a new user (and group) to your system with the following command (this will vary depending on what OS you're running):
Create Installation Directory
Create the base directory where you would like to install Nagios as follows...
Change the owner of the base installtion directory to be the Nagios user and group you added earlier as follows:
chown nagios.nagios /usr/local/nagios
Identify Web Server User
You're probably going to want to issue external commands (like acknowledgements and scheduled downtime) from the web interface. To do so, you need to identify the user your web server runs as (typically apache, although this may differ on your system). This setting is found in your web server configuration file. The following command can be used to quickly determine what user Apache is running as (paths may differ on your system):
grep "^User" /etc/httpd/conf/httpd.conf
Add Command File Group
Next we're going to create a new group whose members include the user your web server is running as and the user Nagios is running as. Let's say we call this new group 'nagcmd' (you can name it differently if you wish). On RedHat Linux you can use the following command to add a new group (other systems may differ):
Next, add the users that your web server and Nagios run as to the newly created group with the following commands (I'll assume apache and nagios are the respective users):
/usr/sbin/usermod -G nagcmd apache
/usr/sbin/usermod -G nagcmd nagios
Run the Configure Script
Run the configure script to initialize variables and create a Makefile as follows...(the last two options: --with-command-xxx are optional, but needed if you want to issue external commands)
./configure --prefix=prefix --with-cgiurl=cgiurl --with-htmurl=htmurl --with-nagios-user=someuser --with-nagios-group=somegroup --with-command-group=cmdgroup
Compile Nagios and the CGIs with the following command:
Installing The Binaries And HTML Files
Install the binaries and HTML files (documentation and main web page) with the following command:
Installing An Init Script
If you wish, you can also install the sample init script to /etc/rc.d/init.d/nagios with the following command:
You may have to edit the init script to make sense with your particular OS and Nagios installation by editing paths, etc.
Directory Structure And File Locations
Change to the root of your Nagios installation directory with the following command...
You should see five different subdirectories. A brief description of what each directory contains is given in the table below.
|bin/||Nagios core program|
|etc/||Main, resource, object, and CGI configuration files should be put here|
|share/||HTML files (for web interface and online documentation)|
|var/||Empty directory for the log file, status file, retention file, etc.|
|var/archives||Empty directory for the archived logs|
|var/rw||Empty directory for the external command file|
Installing The Plugins
In order for Nagios to be of any use to you, you're going to have to download and install some plugins. Plugins are usually installed in the libexec/ directory of your Nagios installation (i.e. /usr/local/nagios/libexec). Plugins are scripts or binaries which perform all the service and host checks that constitute monitoring. You can grab the latest release of the plugins from the Nagios downloads page or directly from the SourceForge project page.
Setup The Web Interface
You're probably going to want to use the web interface, so you'll also have to read the instructions on setting up the web interface and configuring web authentication, etc. next.
So now you have things compiled and installed, but you still haven't configured Nagios or defined objects (hosts, services, etc.) that should be monitored. Information on configuring Nagios and defining objects can be found here. There's a lot to configure, but don't let it discourage you - its well worth it.