1 Introduction

1.1 Goals

1.2 Notes

2 Exercises

3 PART IX - Optional Exercises

3.1 1. Check that nagios is Running

As opposed to just checking that a web server is running on the classroom PCs, you could also check that t he nagios3 service is available, by requesting the /nagios3/ path. This means passing extra options to the check_http plugin.

For a description of the available options, type this:

# /usr/lib/nagios/plugins/check_http                    (short help)
# /usr/lib/nagios/plugins/check_http --help         (detailed help)

and of course you can browse the online nagios documentation or google for information on check_http. You can even run the plugin by hand to perform a one-shot service check:

# /usr/lib/nagios/plugins/check_http -H localhost -u /nagios3/

So the goal is to configure nagios to call check_http in this way.

{hint, /etc/nagios-plugins/config/http.cfg)

define command{
        command_name    check_http_url
        command_line    /usr/lib/nagios/plugins/check_http -H '$HOSTADDRESS$' -u '$ARG1$'
        }

    (hint, /etc/nagios3/conf.d/services_nagios2.cfg_

define service {
        hostgroup_name                  nagios-servers
        service_description             NAGIOS
        check_command                   check_http_url!/nagios3/
        use                             generic-service
}

and of course you'll need to create a hostgroup called nagios-servers to link to this service check. (hint, /etc/nagios3/conf.d/hostgroups_nagios2.cfg)

Once you have done this, check that Nagios warns you about failing authentication (because it's trying to fetch the page without providing the username/password). There's an extra parameter you can pass to check_http to provide that info, so we need to define a new command with an additional argument:

define command{
        command_name    check_http_url_auth
        command_line    /usr/lib/nagios/plugins/check_http -H '$HOSTADDRESS$' -u '$ARG1$' -a '$ARG2$'
        }

And you invoke it:

check_command                   check_http_url_auth!/nagios3/!nagiosadmin:password

WARNING: in the tradition of "Debian Knows Best", their definition of the check_http command in /etc/nagios-plugins/config/http.cfg is not the same as that recommended in the nagios3 documentation. It is missing ARG1, so any parameters to pass to check_http are ignored. So you might think you are monitoring /nagios3/ but actually you are monitoring root!

This is why we had to make a new command definition "check_http_url". You could make a more specific one like "check_nagios", or you could modify the Ubuntu check_http definition to fit the standard usage.

3.2 2. Check that SNMP is running on the classroom NOC

This exercise will not work if you did not complete the installation of additional SNMP MIBs at the start of the week and configure /etc/snmp/snmp.conf properly. Please refer to the original snmp exercises if you are unsure.

First you will need to add in the appropriate service check for SNMP in the file /etc/nagios3/conf.d/services_nagios2.cfg. This is where Nagios is impressive. There are hundreds, if not thousands, of service checks available via the various Nagios sites on the web. You can see what plugins are installed by Ubuntu in the nagios3 package that we've installed by looking in the following directory:

# ls /usr/lib/nagios/plugins

As you'll see there is already a check_snmp plugin available to us. If you are interested in the options the plugin takes you can execute the plugin from the command line by typing:

# /usr/lib/nagios/plugins/check_snmp                    (short help)
# /usr/lib/nagios/plugins/check_snmp --help                 (detailed help)

to see what options are available, etc. You can use the check_snmp plugin and Nagios to create very complex or specific system checks.

Now to see all the various service/host checks that have been created using the check_snmp plugin you can look in /etc/nagios-plugins/config/snmp.cfg. You will see that there are a lot of preconfigured checks using snmp, including:

      snmp_load
      snmp_cpustats
      snmp_procname
      snmp_disk
      snmp_mem
      snmp_swap
      snmp_procs
      snmp_users
      snmp_mem2
      snmp_swap2
      snmp_mem3
      snmp_swap3
      snmp_disk2
      snmp_tcpopen
      snmp_tcpstats
      snmp_bgpstate
      check_netapp_uptime
      check_netapp_cupuload
      check_netapp_numdisks
      check_compaq_thermalCondition

And, even better, you can create additional service checks quite easily. For the case of verifying that snmpd (the SNMP service on Linux) is running we need to ask SNMP a question. If we don't get an answer, then Nagios can assume that the SNMP service is down on that host. When you use service checks such as check_http, check_ssh and check_telnet this is what they are doing as well.

In our case, let's create a new service check and call it "check_system". This service check will connect with the specified host, use the private community string we have defined in class and ask a question of snmp on that host - in this case we'll ask about the System Description, or the OID "sysDescr.0" -

To do this start by editing the file /etc/nagios-plugins/config/snmp.cfg:

# editor /etc/nagios-plugins/config/snmp.cfg

At the top (or the bottom, your choice) add the following entry to the file:

# 'check_system' command definition
define command{
       command_name    check_system
       command_line    /usr/lib/nagios/plugins/check_snmp -H '$HOSTADDRESS$' -C '$ARG1$' -o sysDescr.0
    }

COPY and PASTE this. Do not type this by hand and make sure that the command_line line does not wrap.

Note that "command_line" is a single line. If you copy and paste in your editor, the line may not wrap properly and you may have to manually "join" the two lines so they are one.

Now you need to edit the file /etc/nagios3/conf.d/services_nagios2.cfg and add in this service check. We'll run this check against all our servers in the classroom, or the hostgroup "debian-servers"

Edit the file /etc/nagios3/conf.d/services_nagios2.cfg

# editor /etc/nagios3/conf.d/services_nagios2.cfg

At the bottom of the file add the following definition:

# check that snmp is up on all servers
define service {
        hostgroup_name                  snmp-servers
        service_description             SNMP
        check_command                   check_system!xxxxxx
        use                             generic-service
        notification_interval           0 ; set > 0 if you want to be renotified
}

The "xxxxxx" is the community string previously (or to be) defined in class.

Note that we have included our own community string here vs. hard-coding it in the snmp.cfg file earlier. You must change the "xxxxx" to be the snmp community string given in class or this check will not work.

Now we must create the "snmp-servers" group in our hostgroups_nagios2.cfg file. Edit the file /etc/nagios3/conf.d/hostgroups_nagios2.cfg and go to the end of the file. Add in the following hostgroup definition:

# A list of snmp-enabled devices on which we wish to run the snmp service check
define hostgroup {
       hostgroup_name   snmp-servers
               alias    snmp servers
               members  noc,localhost,pc1,pc2,pc3,pc4...pc36,rtr1,rtr2,rtr3...rtr9
      }

Note that for "members" you can add in all PCs and routers as they should all have snmp up and running at this time. Remember to EXCLUDE our pc and use localhost instead.

Now verify that your changes are correct and restart Nagios.

# service nagios3 restart

**** Defect / Bug in Ubuntu 12.04 LTS ***

The net-snmp 5.6.x package appears to not install one of the IANA mibs (IANAifType-MIB). This causes a MIB error, which, in turn causes the snmp check plugin to fail. To fix this problem do the following (as root):

# cd /usr/share/mibs
# wget http://www.iana.org/assignments/ianaiftype-mib/ianaiftype-mib
# mv ianaiftype-mib ianaiftype-mib.my

And, now you can continue.

If you click on the Service Detail menu choice in web interface you should see the SNMP check appear for the noc host, or for any other hosts you may have included on the "members" line above.