What is Nagios?

Nagios is an Open Source system and network monitoring application. It watches hosts and services that you specify, alerting you when things go bad and when they get better. The Open Source utility was originally designed to run under Linux, which I prefer (Ubuntu 10.3 :)). Here is a run down on configuration a Linux box to run Nagios.

­Notes:

• 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/

Preparing Your System:

• First you need to install the following packages
  • sudo apt-get install apache2
  • sudo apt-get install build-essential
  • sudo apt-get install libgd2-xpm-dev
  • sudo apt-get install php5
  • sudo apt-get install libapache2-mod-php5
  • sudo /etc/init.d/apache2 restart

Create Account Information:

• Become the root user.
  • sudo -s

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

• #/usr/sbin/useradd nagios
• #passwd nagios

Notes:

On Ubuntu server edition , you will need to also add a nagios group (it’s not created by default). You should be able to skip this step on desktop editions of Ubuntu.

• #/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 -G nagcmd nagios
• #/usr/sbin/usermod -G nagcmd www-data

Download Nagios and the Plugins:

• Create a directory for storing the downloads.
  • #mkdir ~/downloads
  • #cd ~/downloads
• Download the source code tarballs of both Nagios and the Nagios plugins.
  • #wget http://switch.dl.sourceforge.net/sourceforge/nagios/nagios-3.2.1.tar.gz
  • #wget http://kent.dl.sourceforge.net/sourceforge/nagiosplug/nagios-plugins-1.4.10.tar.gz

Compile and Install Nagios:

• Extract the Nagios source code tarball.
  • #cd ~/downloads
  • #tar xzf nagios-3.2.1.tar.gz
  • #cd nagios-3.2.1
• Run the Nagios configure script, passing the name of the group you created earlier like so:
  • o   #./configure --with-command-group=nagcmd


Compile the Nagios 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

*Don’t start Nagios yet – there’s still more that needs to be done…*

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. 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

Configure the Web Interface:

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

• #make install-webconf

Create a nagiosadmin account for logging into the Nagios 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.

• #/etc/init.d/apache2 reload

Compile and Install the Nagios Plugins:

Extract the Nagios plugins source code tarball.

• #cd ~/downloads
• #tar xzf nagios-plugins-3.2.1.tar.gz
• #cd nagios-plugins-1.4.10

Compile and install the plugins.

• #./configure --with-nagios-user=nagios --with-nagios-group=nagios
• #make
• #make install

Start Nagios:

Configure Nagios to automatically start when the system boots.

• #ln -s /etc/init.d/nagios /etc/rcS.d/S99nagios

Verify the sample Nagios configuration files.

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

If there are no errors, start Nagios.

• #/etc/init.d/nagios start

Login to the Web Interface:

You should now be able to access the Nagios 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 to check all the services associated with your machine, as the checks are spread out over time.

Other Modifications:

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

• #apt-get install mailx

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

• #/etc/init.d/nagios restart

How to change the hostname in Ubuntu

To change hostname in Ubuntu or any Debian variant Linux, modify the /etc/hostname and /etc/hosts.

• sudo vi /etc/hostname

Change the old hostname to a new hostname.

• sudo vi /etc/hosts

Also, change the oldhostname to a new hostname,

• 192.168.1.100               newhostname

After done, changing the /etc/hostname and /etc/hosts, you need to restart the hostname service.

• sudo /etc/init.d/hostname.sh stop
• sudo /etc/init.d/hostname.sh start

And then you log out from the shell and log in back. Once logged in, type

• hostname

to check on the changes you have made for the hostname.

It’s pretty straight forward. Once your done with that I recommend installing ssh on your Linux box, so you can putty into your box :).