~kim0/serverguide/serverguide-review-ch19

<div class="breadcrumbs"><a href="https://help.ubuntu.com/">Ubuntu Documentation</a> > <a href="https://help.ubuntu.com/11.04">Ubuntu 11.04</a> > <span class="breadcrumb-link"><a href="index.html">Ubuntu Server Guide</a></span> > <span class="breadcrumb-link"><a href="monitoring.html">Monitoring</a></span> > <span class="breadcrumb-node">Nagios</span></div>

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<h2 class="title" style="clear: both"><a id="nagios"></a>Nagios</h2>

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<h3 class="title"><a id="nagios-installation"></a>Installation</h3>

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<p>

First, on <span class="emphasis"><em>server01</em></span> install the <span class="application"><strong>nagios</strong></span> package. In a terminal

enter:

</p>

<span class="command"><strong>sudo apt-get install nagios3 nagios-nrpe-plugin</strong></span>

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<p>

You will be asked to enter a password for the <span class="emphasis"><em>nagiosadmin</em></span> user. The user's credentials are

stored in <code class="filename">/etc/nagios3/htpasswd.users</code>. To change the <span class="emphasis"><em>nagiosadmin</em></span> password, or

add additional users to the Nagios CGI scripts, use the <span class="application"><strong>htpasswd</strong></span> that is part of the

<span class="application"><strong>apache2-utils</strong></span> package.

</p>

<p>

For example, to change the password for the <span class="emphasis"><em>nagiosadmin</em></span> user enter:

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<span class="command"><strong>sudo htpasswd /etc/nagios3/htpasswd.users nagiosadmin</strong></span>

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To add a user:

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<span class="command"><strong>sudo htpasswd /etc/nagios3/htpasswd.users steve</strong></span>

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</pre>

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<p>

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Next, on <span class="emphasis"><em>server02</em></span> install the <span class="application"><strong>nagios-nrpe-server</strong></span> package. From a terminal on

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server02 enter:

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</p>

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<span class="command"><strong>sudo apt-get install nagios-nrpe-server</strong></span>

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</pre>

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<p>

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<span class="application"><strong>NRPE</strong></span> allows you to execute local checks on remote hosts. There are other ways of accomplishing

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this through other Nagios plugins as well as other checks.

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</p>

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</td>

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</table>

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</div>

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</div>

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<div>

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<h3 class="title"><a id="nagios-configuration-overview"></a>Configuration Overview</h3>

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</div>

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<p>

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There are a couple of directories containing <span class="application"><strong>Nagios</strong></span> configuration and check files.

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<code class="filename">/etc/nagios3</code>: contains configuration files for the operation of the <span class="application"><strong>nagios</strong></span>

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daemon, CGI files, hosts, etc.

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</p>

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</li>

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<code class="filename">/etc/nagios-plugins</code>: houses configuration files for the service checks.

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</p>

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<code class="filename">/etc/nagios</code>: on the remote host contains the <span class="application"><strong>nagios-nrpe-server</strong></span> configuration files.

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</p>

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<p>

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<code class="filename">/usr/lib/nagios/plugins/</code>: where the check binaries are stored. To see the options of a check use the

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<span class="emphasis"><em>-h</em></span> option.

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</p>

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For example: <span class="command"><strong>/usr/lib/nagios/plugins/check_dhcp -h</strong></span>

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</p>

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</ul>

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</div>

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<p>

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There are a plethora of checks <span class="application"><strong>Nagios</strong></span> can be configured to execute for any given host. For this example Nagios

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will be configured to check disk space, DNS, and a MySQL hostgroup. The DNS check will be on <span class="emphasis"><em>server02</em></span>, and the

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MySQL hostgroup will include both <span class="emphasis"><em>server01</em></span> and <span class="emphasis"><em>server02</em></span>.

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<p>

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See <a class="xref" href="httpd.html" title="HTTPD - Apache2 Web Server">the section called “HTTPD - Apache2 Web Server”</a> for details on setting up Apache, <a class="xref" href="dns.html" title="Chapter 7. Domain Name Service (DNS)">Chapter 7, <i>Domain Name Service (DNS)</i></a> for DNS, and <a class="xref" href="mysql.html" title="MySQL">the section called “MySQL”</a> for MySQL.

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</p>

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</table>

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</div>

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<p>

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Additionally, there are some terms that once explained will hopefully make understanding Nagios configuration easier:

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</p>

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<span class="emphasis"><em>Host</em></span>: a server, workstation, network device, etc that is being monitored.

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</p>

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<span class="emphasis"><em>Host Group</em></span>: a group of similar hosts. For example, you could group all web servers, file server, etc.

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<span class="emphasis"><em>Service</em></span>: the service being monitored on the host. Such as HTTP, DNS, NFS, etc.

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</p>

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<span class="emphasis"><em>Service Group</em></span>: allows you to group multiple services together. This is useful for grouping multiple HTTP

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for example.

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<p>

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<span class="emphasis"><em>Contact</em></span>: person to be notified when an event takes place. Nagios can be configured to send emails, SMS messages, etc.

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</p>

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</ul>

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<p>

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By default Nagios is configured to check HTTP, disk space, SSH, current users, processes, and load on the <span class="emphasis"><em>localhost</em></span>.

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Nagios will also <span class="application"><strong>ping</strong></span> check the <span class="emphasis"><em>gateway</em></span>.

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</p>

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Large Nagios installations can be quite complex to configure. It is usually best to start small, one or two hosts, get things configured the way you like

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then expand.

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</p>

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</div>

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<div>

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<div>

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<h3 class="title"><a id="nagios-configuration"></a>Configuration</h3>

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</div>

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</div>

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</div>

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<p>

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First, create a <span class="emphasis"><em>host</em></span> configuration file for <span class="emphasis"><em>server02</em></span>.

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Unless otherwise specified, run all these commands on <span class="emphasis"><em>server01</em></span>.

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In a terminal enter:

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</p>

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<span class="command"><strong>sudo cp /etc/nagios3/conf.d/localhost_nagios2.cfg /etc/nagios3/conf.d/server02.cfg</strong></span>

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</pre>

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<p>

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In the above and following command examples, replace <span class="emphasis"><em>"server01"</em></span>, <span class="emphasis"><em>"server02"</em></span>

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<span class="emphasis"><em>172.18.100.100</em></span>, and <span class="emphasis"><em>172.18.100.101</em></span> with the host names and IP addresses

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of your servers.

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<p>

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Next, edit <code class="filename">/etc/nagios3/conf.d/server02.cfg</code>:

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</p>

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define host{

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use generic-host ; Name of host template to use

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host_name server02

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alias Server 02

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address 172.18.100.101

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}

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# check DNS service.

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define service {

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use generic-service

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host_name server02

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service_description DNS

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check_command check_dns!172.18.100.101

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}

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</pre>

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<p>

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Restart the <span class="application"><strong>nagios</strong></span> daemon to enable the new configuration:

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<span class="command"><strong>sudo /etc/init.d/nagios3 restart</strong></span>

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</pre>

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</ol>

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</div>

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<p>

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Now add a service definition for the MySQL check by adding the following to <code class="filename">/etc/nagios3/conf.d/services_nagios2.cfg</code>:

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</p>

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# check MySQL servers.

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define service {

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hostgroup_name mysql-servers

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service_description MySQL

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check_command check_mysql_cmdlinecred!nagios!secret!$HOSTADDRESS

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use generic-service

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notification_interval 0 ; set > 0 if you want to be renotified

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}

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</pre>

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<p>

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A <span class="emphasis"><em>mysql-servers</em></span> hostgroup now needs to be defined. Edit

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<code class="filename">/etc/nagios3/conf.d/hostgroups_nagios2.cfg</code> adding:

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</p>

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# MySQL hostgroup.

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define hostgroup {

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hostgroup_name mysql-servers

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alias MySQL servers

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members localhost, server02

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}

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</pre>

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<p>

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The Nagios check needs to authenticate to MySQL. To add a <span class="emphasis"><em>nagios</em></span> user to MySQL enter:

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<span class="command"><strong>mysql -u root -p -e "create user nagios identified by 'secret';"</strong></span>

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</pre>

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The <span class="emphasis"><em>nagios</em></span> user will need to be added all hosts in the <span class="emphasis"><em>mysql-servers</em></span> hostgroup.

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Restart <span class="application"><strong>nagios</strong></span> to start checking the MySQL servers.

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<span class="command"><strong>sudo /etc/init.d/nagios3 restart</strong></span>

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</pre>

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Lastly configure NRPE to check the disk space on <span class="emphasis"><em>server02</em></span>.

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On <span class="emphasis"><em>server01</em></span> add the

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service check to <code class="filename">/etc/nagios3/conf.d/server02.cfg</code>:

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# NRPE disk check.

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define service {

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use generic-service

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host_name server02

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service_description nrpe-disk

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check_command check_nrpe_1arg!check_all_disks!172.18.100.101

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}

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</pre>

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Now on <span class="emphasis"><em>server02</em></span> edit <code class="filename">/etc/nagios/nrpe.cfg</code> changing:

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allowed_hosts=172.18.100.100

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</pre>

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And below in the command definition area add:

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command[check_all_disks]=/usr/lib/nagios/plugins/check_disk -w 20% -c 10% -e

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</pre>

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Finally, restart <span class="application"><strong>nagios-nrpe-server</strong></span>:

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<span class="command"><strong>sudo /etc/init.d/nagios-nrpe-server restart</strong></span>

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</pre>

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<p>

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Also, on <span class="emphasis"><em>server01</em></span> restart <span class="application"><strong>nagios</strong></span>:

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<span class="command"><strong>sudo /etc/init.d/nagios3 restart</strong></span>

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</pre>

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</ol>

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</div>

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</ul>

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<p>

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You should now be able to see the host and service checks in the Nagios CGI files. To access them point a

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browser to http://server01/nagios3. You will then be prompted for the <span class="emphasis"><em>nagiosadmin</em></span> username

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and password.

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</p>

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</div>

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<h3 class="title"><a id="nagios-references"></a>References</h3>

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</div>

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</div>

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<p>

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This section has just scratched the surface of Nagios' features. The <span class="application"><strong>nagios-plugins-extra</strong></span> and

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<span class="application"><strong>nagios-snmp-plugins</strong></span> contain many more service checks.

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</p>

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For more information see <a class="ulink" href="http://www.nagios.org/" target="_top">Nagios</a> website.

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Specifically the <a class="ulink" href="http://nagios.sourceforge.net/docs/3_0/" target="_top">Online Documentation</a> site.

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<p>

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There is also a list of <a class="ulink" href="http://www.nagios.org/propaganda/books/" target="_top">books</a> related to Nagios

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and network monitoring:

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</p>

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The <a class="ulink" href="https://help.ubuntu.com/community/Nagios" target="_top">Nagios Ubuntu Wiki</a> page also has more details.

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</p>

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</ul>

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<hr />

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</a>

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<td width="40%" align="left" valign="top">Overview </td>

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</a>

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</td>

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<td width="40%" align="right" valign="top"> Munin</td>

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</table>

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<hr />

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<p>The material in this document is available under a free license, see <a href="/legal.html">Legal</a> for details<br />

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For information on contributing see the <a href="https://wiki.ubuntu.com/DocumentationTeam">Ubuntu Documentation Team wiki page</a>. To report a problem, visit the <a href="https://bugs.launchpad.net/ubuntu/+source/ubuntu-docs">bug page for Ubuntu Documentation</a></p>

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</body>

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