Configure Nagios Hosts and Services

Now that you have Nagios installed (See last week’s article:  “Monitoring Your Systems with Nagios” ), you are ready to begin monitoring services such as ssh, websites, and other services.  So that brings us to the purpose of this week’s article:  How to Configure Nagios Hosts and Services.  To do this, we have two general tasks:

• Create a file with host and service definitions for the host that we intend to monitor and
• edit the nagios.cfg file to tell it about our new file containing the host and service definitions.

Define New Files and Directories in the Nagios.cfg File

Let’s start by editing the nagios.cfg.  If you installed with me using last week’s article:  “Monitoring Your Systems with Nagios”, then your nagios.cfg file will be located at:  /usr/local/nagios/etc/nagios.cfg.  We will edit it and file the location where the other cfg_file and cfg_dir definitions are located and add these lines:

cfg_file=/usr/local/nagios/etc/objects/hostgroups.cfg

and

cfg_dir=/usr/local/nagios/etc/objects/hosts

Define Nagios Hostgroups

Now, we need to create a hostgroup to put our hosts in.  Hostgroups allow us to group our hosts by OS, by service they provide, by location, etc…  In this case, I will just make one hostgroup named:  webservers and put my one host in it.

We defined the location of our hostgroup file above in the nagios.cfg file.  Let’s change to that location now:

cd /usr/local/nagios/etc/objects

Create the hostgroups.cfg file:

define hostgroup{
hostgroup_name  webservers
alias           Very Important WebServers
}

Later, we can define any other hostgroups that we want to use for our organizational efforts in this same file.

Define or Configure Nagios Hosts and Services

With the hostgroup defined, let’s define our host.  We defined a directory above to put our host definitions in the nagios.cfg file.  We can put all of our host definitions in this directory.  The only requirement now is that the files end with a .cfg extension.  Let’s now create it and change into it:

mkdir /usr/local/nagios/etc/objects/hosts; cd /usr/local/nagios/etc/objects/hosts

The next step in our task to Configure Nagios Hosts and Services is the host definition.

Now, we create a file for our host definition.  Typically, I put the service definitions for my host in the same file as the host itself.  Create a filename to define your host.  The filename must have a .cfg extension.  In my case it is named:  uptimemadeeasy.cfg

define host{
use                   linux-server
host_name               uptimemadeeasy.com
alias                   uptimemadeeasy.com website
address                 uptimemadeeasy.com
hostgroups              webservers
retry_check_interval    2
contact_groups          admins
notification_interval   15
notification_period     24×7
notification_options    d,u,r,f,s
notifications_enabled   1
}

and below the host definition in the same file we put our service definitions:

define service{
use                     generic-service
host_name               uptimemadeeasy.com
service_description     ssh
check_command           check_ssh
check_period            24×7
check_interval          5
max_check_attempts      3
normal_check_interval   3
retry_check_interval    2
contact_groups          admins
notification_interval   60
notification_period     24×7
notification_options    w,c,u,r
notifications_enabled   1
}

define service{
use                     generic-service
host_name               uptimemadeeasy.com
service_description     http
check_command           check_http
check_period            24×7
check_interval          5
max_check_attempts      2
normal_check_interval   5
retry_check_interval    1
contact_groups          admins
notification_interval   15
notification_period     24×7
notification_options    w,c,u,r
}

With all of that done.  We should be ready to verify our configuration is correct, restart the nagios service and login to see the definition.

Verify the Nagios Configuration:

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

Be sure that there are no errors or warnings in the check.  Then, restart Nagios:

/sbin/service nagios restart

Now let’s login and check out our host and it’s services:

We have now defined one host with its two services.

You can see that Nagios is able to successfully check the services we defined and they end up green with an OK status.

Next week, we will discuss using NRPE to perform checks through plugins on a remote system in the article:  Nagios Remote Plugins with NRPE

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Jeff Staten

Jeff has 20 years of professional IT experience, having done nearly everything in his roles of IT consultant, Systems Integrator, Systems Engineer, CNOC Engineer, Systems Administrator, Network Systems Administrator, and IT Director. If there is one thing he knows for sure, it is that there is always a simple answer to every IT problem and that downtime begins with complexity. Seasoned IT professional by day, Jeff hopes to help other IT professionals by blogging about his experiences at night on his blog: http://uptimemadeeasy.com. You can find Jeff on Google+ or LinkedIn at: LinkedIn or Twitter at: Twitter

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