I’ve been running Nagios on my systems at home (yes, I’m that big of a nerd) for a week or so, but didn’t get around to setting up e-mail alerts until now. There are a few ways to go about doing this, but I’ll describe the way I got it going. Since I’m not running a mail server on any of my machines I use Google Apps to handle e-mail for my domains. I rather have ‘the Google’ deal with all of that for me (and they do a great job).
For this particular instance I was running Ubuntu Server 8.04.4 LTS, but these steps should work fine on other versions and distros.
1. Install sSMTP and mailx
sudo apt-get install ssmtp mailx
2. Configure sSMTP by editing /etc/ssmtp/ssmtp.conf
# Config file for sSMTP sendmail
# The person who gets all mail for userids < 1000
# Make this empty to disable rewriting.
root=[your user account]@[yourdomain.com]
# The place where the mail goes. The actual machine name is required no
# MX records are consulted. Commonly mailhosts are named mail.domain.com
# Where will the mail seem to come from?
# The full hostname
hostname=[some hostname here]
AuthUser=[your user account]@[your domain]
# Are users allowed to set their own From: address?
# YES - Allow the user to specify their own From: address
# NO - Use the system generated From: address
# This is optional if you're going to use revaliases - I didn't
3. Lock down /etc/ssmtp/ssmtp.conf to help protect your plaintext password
sudo chown root:nagcmd /etc/ssmtp/ssmtp.conf
sudo chmod 640 /etc/ssmtp/ssmtp.conf
4. Alter your Nagios commands.cfg file for the correct mail path (for Ubuntu at least)
sudo vim /usr/local/nagios/etc/objects/commands.cfg
And change all instances of /bin/mail to /usr/bin/mail. Be sure to reload your Nagios configuration after making these changes.
That should be it! If you’re having trouble, break things down to troubleshoot. First test out sSMTP by doing the following:
sudo -vvv ssmtp firstname.lastname@example.org
Write a message, press enter, then hit CTRL+D. If that works successfully but Nagios still isn’t sending alerts, be sure to check the Event Log in the Nagios interface to see if there are any errors.