Creating a Nagios plug-in looks daunting and hard at first. It’s really not as hard as you think.
Here is a couple things you should know:

Know what you want to monitor.
I create most of my plug-ins in bash scripts and perl scripts. (other languages supported, those are just what I use)
Know your exit codes.
Your plug-in output should be helpful and informative.

Exit codes are simple, and key to your plug-in success.

0 – OK
1 – WARN
2 – CRITICAL
3 – UKNOWN

Now those look family don’t they, they are the states or status of a service. i.e. my disk space is in OK state because I have 120GB free space.

here is a sample code snippet:

if [ $space -ge $CRITCAL ] ; then
echo "DISK SPACE CRITICAL - 90% disk space used [10GB free on /]"
exit 2;
fi

Need Nagios/Monitoring consulting? Maybe I can help, I am currently working on, as project lead, one of the biggest Nagios installs, for a Wal-Mart and Novell.

So yesterday I had Enviro-Air (of Springfield, MO)  come out to to clean our air ducts in the house, you can read previous post about this.   The service tech’s showed up around 10am and started working on the system.  They where professional and did a great job.  After all was done, they finished things off, put together the furnace and attempted to fire it up, no luck.  After a few attempts they notice they hooked the blower wiring up to the wrong thing. (two white wires) After again getting shocked a few more times, they decided to call in a repair man.  It’s almost noon the next day and I’m still out of a A/C unit.   It’s around 80 in the house as I write this, I have the attic fan on, the rest of the family is up at the in-laws keeping cool. 

Here are some pics from yesterdays cool equipment they had: 

Today I had a estimate done on cleaning our HVAC and Duct work in our house.  Why, well our house is 15 years old now, I don’t think it had ever been cleaned and the returns are a royal mess filled with dust. Not a good thing.   Here is the break down.

• Furnace Cleaning (including Blower and A-Coil)   $130
• Cleaning per supply   $20 ( I have 21 supply feeds )
• Cleaning per return    $30 ( I have 3 return feeds )
• Optional -Anti-Microbial/ Deodorizer Treatment   $70