Installing Nagios

Reference 1: Nagios and Nginx on Ubuntu 12.04 LTS
Reference 2: Ubuntu quickstart guide to installing Nagios.

Development files and packages
libssl-dev is the development files needed for compiling Nagios plugins. Without this you will encounter errors while compiling Nagios plugins.

sudo apt-get install apache2 libapache2-mod-php5 \
build-essential libssl-dev libgd2-xpm-dev -y

Create user and group

Create user and group for nagios, also create another group for external command executed via nagios.

Create a user nagios and disable nagios from gaining shell access by assigning nagios to /bin/false shell. nagios will also never be able to login to the Ubuntu linux shell.

sudo useradd -m -s /bin/false nagios
sudo groupadd nagios
sudo usermod -G nagios nagios
sudo groupadd nagcmd
sudo usermod -a -G nagcmd www-data
sudo usermod -a -G nagcmd nagios

Verify:

cyruslab@Nachos:/$ cat /etc/group | grep nagios
nagios:x:1001:nagios
nagcmd:x:1002:www-data,nagios
cyruslab@Nachos:/$

To remove a user from a group use the gpasswd command, example gpasswd -d www-data nagcmd removes www-data user from nagcmd group.

Download nagios and plugins

cyruslab@Nachos:/bin$ cd /tmp/
cyruslab@Nachos:/tmp$  wget http://prdownloads.sourceforge.net/sourceforge/nagios/nagios-3.4.1.tar.gz
cyruslab@Nachos:/tmp$  wget http://prdownloads.sourceforge.net/sourceforge/nagiosplug/nagios-plugins-1.4.16.tar.gz

Untar and unzip the files:

cyruslab@Nachos:/tmp$ tar -zxvf nagios-3.4.1.tar.gz
cyruslab@Nachos:/tmp$ tar -xzvf nagios-plugins-1.4.16.tar.gz

Compile and install
Configure the source code:

cyruslab@Nachos:/tmp/nagios$ ./configure --with-nagios-user=nagios --with-nagios-group=nagios \
> --with-command-user=nagios --with-command-group=nagcmd --sysconfdir=/etc/nagios

Compile the source code locally and install the compiled code:

cyruslab@Nachos:/tmp/nagios$ make all && sudo make install

Installs the init scripts to /etc/init.d

cyruslab@Nachos:/tmp/nagios$ sudo make install-init

Installs and configures permissions on the directory for holding the external command file.

cyruslab@Nachos:/tmp/nagios$ sudo make install-commandmode

Installs sample config files in /etc/nagios

cyruslab@Nachos:/tmp/nagios$ sudo make install-config

Install nagios web config file to apache2

cyruslab@Nachos:/tmp/nagios$ sudo make install-webconf

Customize the username authorized to access nagios

cyruslab@Nachos:/tmp/nagios$ cd /etc/nagios/
cyruslab@Nachos:/etc/nagios$ sudo nano cgi.cfg

Change these parameters all to any username you like to access, for me I changed all the parameters from nagiosadmin to admin or just add admin with a comma after nagiosadmin:
1. authorized_for_system_information
2. authorized_for_configuration_information
3. authorized_for_system_commands
4. authorized_for_all_service_commands
5. authorized_for_all_host_commands

This step is not necessary however i felt nagiosadmin is a bit long for username.

#It is not necessary to create htpasswd.users yourself, htpasswd will create the file.
cyruslab@Nachos:~$ sudo htpasswd -c /etc/nagios/htpasswd.users admin
New password:
Re-type new password:
Adding password for user admin
cyruslab@Nachos:~$

Configure nagios-plugins source code, compile and install:

cyruslab@Nachos:/tmp/nagios$ cd ../nagios
cyruslab@Nachos:/tmp/nagios-plugins-1.4.16$ ./configure --with-nagios-user=nagios --with-nagios-group=nagios
cyruslab@Nachos:/tmp/nagios-plugins-1.4.16$ make && sudo make install

To start nagios automatically everytime system boot
Create symbolic link:

cyruslab@Nachos:/tmp/nagios-plugins-1.4.16$ sudo ln -s /etc/init.d/nagios /etc/rcS.d/S99nagios

Verify nagios config

cyruslab@Nachos:/tmp/nagios-plugins-1.4.16$ sudo /usr/local/nagios/bin/nagios -v /etc/nagios/nagios.cfg

Nagios Core 3.4.1
Copyright (c) 2009-2011 Nagios Core Development Team and Community Contributors
Copyright (c) 1999-2009 Ethan Galstad
Last Modified: 05-11-2012
License: GPL

Website: http://www.nagios.org
Reading configuration data...
   Read main config file okay...
Processing object config file '/etc/nagios/objects/commands.cfg'...
Processing object config file '/etc/nagios/objects/contacts.cfg'...
Processing object config file '/etc/nagios/objects/timeperiods.cfg'...
Processing object config file '/etc/nagios/objects/templates.cfg'...
Processing object config file '/etc/nagios/objects/localhost.cfg'...
   Read object config files okay...

Running pre-flight check on configuration data...

Checking services...
        Checked 8 services.
Checking hosts...
        Checked 1 hosts.
Checking host groups...
        Checked 1 host groups.
Checking service groups...
        Checked 0 service groups.
Checking contacts...
        Checked 1 contacts.
Checking contact groups...
        Checked 1 contact groups.
Checking service escalations...
        Checked 0 service escalations.
Checking service dependencies...
        Checked 0 service dependencies.
Checking host escalations...
        Checked 0 host escalations.
Checking host dependencies...
        Checked 0 host dependencies.
Checking commands...
        Checked 24 commands.
Checking time periods...
        Checked 5 time periods.
Checking for circular paths between hosts...
Checking for circular host and service dependencies...
Checking global event handlers...
Checking obsessive compulsive processor commands...
Checking misc settings...

Total Warnings: 0
Total Errors:   0

Things look okay - No serious problems were detected during the pre-flight check
cyruslab@Nachos:/tmp/nagios-plugins-1.4.16$

Start the services

Start nagios and apache2:

sudo service nagios start
sudo service apache2 start

500 internal server error

If you encounter the 500 internal server error it could be because the htpasswd.users is not located, check nagios.cfg to see if the htpasswd path is the same you have provided using the htpasswd -c command.

Nagios

Nagios tactical overview

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