LinuxReaders

This post will cover step by step Nagios installation.
In current world everything is available online, every organization is trying to reduce their downtime. Almost all Data Centers are running hundreds of services. It is not possible for human being to monitor all services, this is where Nagios is useful. Administrator can use Nagios to monitor all hosts, services, network devices.

Nagios can be configured to check critical services on different time intervals. And can be used to send Email alerts to system admins.

Here I will cover installation, host & service configuration, service details,

Installation:
Download Nagios & Nagios-plugins from http://www.nagios.org/download/
assuming you have stored source packages in /downloads/

(I prefer to use /tmp/ for package installation)

cd /tmp
tar zxvf /downloads/nagios-3.0.6.tar.gz

cd nagios-3.0.6/
./configure
make all

useradd nagios

# need to add nagios user

make install

# – This installs the main program, CGIs, and HTML files

make install-init

# – This installs the init script in /etc/rc.d/init.d

make install-commandmode

#- This installs and configures permissions on the
# directory for holding the external command file

make install-config

# – This installs *SAMPLE* config files in /usr/local/nagios/etc
# You’ll have to modify these sample files before you can
# use Nagios. Read the HTML documentation for more info
# on doing this. Pay particular attention to the docs on
# object configuration files, as they determine what/how
# things get monitored!

make install-webconf

#- This installs the Apache config file for the Nagios
# web interface

service nagios restart
service httpd restart

# for Nagios web authentication.

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

This was all required to start Nagios server.
Now will install nagios-plugins

cd /tmp
tar zxvf /downloads/nagios-plugins-1.4.13.tar.gz
cd nagios-plugins-1.4.13/
./configure –libexecdir=/usr/local/nagios/libexec/
make all
make install

This was all required to start Nagios server with limited available plugins.
By default during installation localhost is configured with few services.

You can access Nagios using http://nagios_server_ip/nagios (it will prompt you for authentication, use nagiosadmin as user & password you entered while creating htpasswd.users).
Nagios panel will display only localhost, if you can see status of localhost you can continue adding hosts & services.

To add more hosts.
I recommend to create separate host files in /usr/local/nagios/etc/objects/ e.g linux.cfg, windows.cfg, router.cfg etc. If you are planning to put all your services to monitor, you can segregate configuration files as per requirement. It helps to easily search & modify configuration whenever required.

You need to mention created .cfg files in /usr/local/nagios/etc/nagios.conf e.g cfg_file=/usr/local/nagios/etc/objects/linux.cfg This will guide Nagios to load manually created configuration files.

cd /usr/local/nagios/etc/objects
Followings is the contains of sample linux.cfg file.

#Linux
define host{
use generic-host ; Name of host template to use
host_name Linux
alias Linux
address 192.168.1.12
check_command check-host-alive
max_check_attempts 10
check_period 24×7
notification_interval 120
notification_period 24×7
notification_options d,r
contact_groups admins
}

#ping
define service{
use generic-service ; Name of service template to use
host_name Linux
service_description PING
is_volatile 0
check_period 24×7
max_check_attempts 4
normal_check_interval 5
retry_check_interval 1
contact_groups admins
notification_options w,u,c,r
notification_interval 960
notification_period 24×7
check_command check_ping!100.0,20%!500.0,60%
}

#http
define service{
use generic-service ; Name of service template to use
host_name Linux
service_description HTTP
is_volatile 0
check_period 24×7
max_check_attempts 4
normal_check_interval 5
retry_check_interval 1
contact_groups admins
notification_options w,u,c,r
notification_interval 960
notification_period 24×7
check_command check_http
}
#smtp
define service{
use generic-service ; Name of service template to use
host_name Linux
service_description SMTP
is_volatile 0
check_period 24×7
max_check_attempts 4
normal_check_interval 5
retry_check_interval 1
contact_groups admins
notification_options w,u,c,r
notification_interval 960
notification_period 24×7
check_command check_smtp
}

/usr/local/nagios/bin/nagios -v ../nagios.cfg (to check nagios configuration)
service nagios reload

Click for service related details. Refer to section Service Definition
I have added Linux host in hostgroup available in localhost.cfg
Recommended way is to create separate groups.cfg.

Now you should be able to see Linux (host) on nagios panel.

To add more timeperiods & contacts you can refer to default config of timeperiods.cfg &

contacts.cfg respectively.