First off, What is nagios?<\/h2>\n\n\n\n
Before I jump on google, lookup Wikipedia or the nagios.org website, I wanted to come up with my own definition. <\/p>\n\n\n\n
Nagios is network monitoring and alerting software. <\/p>\n\n\n\n
It monitors your network using plugins, the plugins are written using a variety of programming and scripting languages, C, bash scripts, pearl, python, php, you can write plugins in basic, SQL, and assembly, it has to return an exit code and some text. <\/p>\n\n\n\n
Based on the exit code, nagios can take action, like send an alert via email, sms, or text message.<\/p>\n\n\n\n
That to me is what Nagios is, the magic is in the plugins. To be fair, nagios does a lot more things, there is a search feature, escalations, a map, and agents that can run on the host.<\/p>\n\n\n\n
Nagios can be a beast if you try to take it all in at one time. I have been using nagios for close to 2 decades, and I still find interesting things for it to do.<\/p>\n\n\n\n
With that said, I must break nagios down from one giant meal in to 5 edible parts:<\/p>\n\n\n\n
- Part 1 – Monitoring Hosts<\/li>
- Part 2 – Monitoring Services<\/li>
- Part 3 – Plugins<\/li>
- Part 4 – NRPE<\/li>
- Part 5 – Notifications, Escalation, and Automated Scripts<\/li><\/ul>\n\n\n\n
What is host monitoring<\/h1>\n\n\n\n
Nagios monitors hosts and services. In this first article we are going to monitor hosts. <\/p>\n\n\n\n
When you want to check if a machine on your network is up, you can do it several ways, you can try to connect to it with Remote Desktop if it is a Windows box, or SSH if it is a Linux box. If it is an appliance, we can check if a Web Management Interface is up. The most common way though, is to ping. It is common to open up a command line and type ping 192.168.1.1 to see if something is up. Or ping 8.8.8.8 as a way to see if your internet is up by pinging Google\u2019s DNS server.<\/p>\n\n\n\n
Setting Things Up<\/h1>\n\n\n\n
First thing we will do is tweak the environment a bit to make it easier to use.<\/p>\n\n\n\n
It is assumed you have installed nagios and have it running (see prior article). But all you see when you log in is localhost when you click on the Hosts section<\/p>\n\n\n\n
![\"\"](\"https:\/\/my.apolonio.tech\/wp-content\/uploads\/2021\/03\/Part-1-Only-Localhost.jpg\")
Only localhost here<\/figcaption><\/figure>\n\n\n\n Log in to the nagios box as root and go to \/etc\/nagios<\/p>\n\n\n\n
Edit the nagios.cfg file<\/p>\n\n\n\n
vi \/etc\/nagios\/nagios.cfg<\/code><\/p>\n\n\n\nGot to around line 51 and uncomment the following<\/p>\n\n\n\n
#cfg_dir=\/etc\/nagios\/servers
#cfg_dir=\/etc\/nagios\/printers
#cfg_dir=\/etc\/nagios\/switches
#cfg_dir=\/etc\/nagios\/routers<\/code><\/p>\n\n\n\nRemove the # sign and make it look like this<\/p>\n\n\n\n
cfg_dir=\/etc\/nagios\/servers
cfg_dir=\/etc\/nagios\/printers
cfg_dir=\/etc\/nagios\/switches
cfg_dir=\/etc\/nagios\/routers<\/code><\/p>\n\n\n\nNow create folders with those names<\/p>\n\n\n\n
mkdir \/etc\/nagios\/servers
mkdir \/etc\/nagios\/printers
mkdir \/etc\/nagios\/switches
mkdir \/etc\/nagios\/routers<\/code><\/p>\n\n\n\nAlthough you do not have to, it is good practice to give ownership of those folders (and any config files you create) nagios ownership.<\/p>\n\n\n\n
chown nagios:nagios \/etc\/nagios\/servers
chown nagios:nagios \/etc\/nagios\/printers
chown nagios:nagios \/etc\/nagios\/switches
chown nagios:nagios \/etc\/nagios\/routers<\/code><\/p>\n\n\n\nIMPORTANT
<\/u><\/strong>Every time you make a change or add something to nagios, test the config first using the following command<\/p>\n\n\n\nnagios -v \/etc\/nagios\/nagios.cfg<\/code><\/p>\n\n\n\nIf there are no errors, you can restart the nagios service<\/p>\n\n\n\n
![\"\"](\"https:\/\/my.apolonio.tech\/wp-content\/uploads\/2021\/03\/Part-1-No-Errors.jpg\")
<\/figure>\n\n\n\nsystemctl restart nagios<\/code><\/p>\n\n\n\nAdding the first host<\/h1>\n\n\n\n
Go in to \/etc\/nagios\/servers and create a file for your first host with the extension .cfg, the name can be anything, but make it easy on yourself and use the name of the host. <\/p>\n\n\n\n
cd \/etc\/nagios\/servers
vi alpha.cfg<\/code><\/p>\n\n\n\nIn the example above, the server I will be monitoring is alpha, a raspberry pi in my lab that does DNS, Time and DHCP on my network.<\/p>\n\n\n\n
Populate the file with the following content, modify your file to match what you have on your network.<\/p>\n\n\n\n
define host{
host_name alpha
address 192.168.80.10
max_check_attempts 10
check_period 24x7
contacts larry,standard
contact_groups admins
notification_interval 120
notification_period 24x7
}<\/code><\/p>\n\n\n\nThis is how a host entry with the minimal parameters looks like in nagios. You can put all your hosts into a single file. But for management I recommend creating an individual file for each of your hosts.<\/p>\n\n\n\n
Test your new config then restart nagios if there are no warnings<\/p>\n\n\n\n
nagios -v \/etc\/nagios\/nagios.cfg
systemctl restart nagios<\/code><\/p>\n\n\n\nGo back to your browser and hit refresh, you will see two entries.<\/p>\n\n\n\n
![\"\"](\"https:\/\/my.apolonio.tech\/wp-content\/uploads\/2021\/03\/Part-1-First-Nagios-Host.jpg\")
<\/figure>\n\n\n\nNormally within 5 minutes (the default), a check would have cycled through and the new host will go from pending to up. But there is a missing parameter, check_command, which is not required, but if it is not defined then the default is to not actively check the host. So we will add the check_command <\/a>parameter with the check-host-alive value, so your config file looks like this.<\/p>\n\n\n\n
![\"\"](\"https:\/\/my.apolonio.tech\/wp-content\/uploads\/2021\/03\/Part-1-First-Nagios-Green-Host.jpg\")
<\/figure>\n\n\n\n![\"\"](\"https:\/\/my.apolonio.tech\/wp-content\/uploads\/2021\/03\/Part-1-Alpha-Info.jpg\")
<\/figure>\n\n\n\n![\"\"](\"https:\/\/my.apolonio.tech\/wp-content\/uploads\/2021\/03\/Part-1-Multiple-Hosts.jpg\")
<\/figure>\n\n\n\n![\"\"](\"https:\/\/my.apolonio.tech\/wp-content\/uploads\/2021\/03\/Part-1-hostgroups.jpg\")
<\/figure>\n\n\n\n