Tip of the Trade: Nagios Plugins

The excellent open-source monitoring
software Nagios is set up to use plugins to do the actual work of checking services. Here are
some useful plugins from the official
plugin site and an unofficial
plugin collection.

Nagios is set up to use plugins to do the actual work of checking services. From cron-apt to check_jabber and more, here are some to get you started.

• check_apt:
  Checks for apt software updates. The main advantage
  over cron-apt is that you can centralize your package monitoring: easier to refer to, and more obvious if a machine is missing.

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• check_jabber:
  The most useful aspect of this is the -D option, which warns
  when your jabber server certificate is close to expiring. Command-line
  options mean you can fine-tune what you send to the server and what
  you expect back.
• check_mysql:
  By default this will check the local
  database anonymously. You can specify username, hostname, and so on, but
  be warned: Any password will be sent clear-text! A very useful feature is
  the ability to check whether the slave server is keeping up with the master
  server.
• check_krb5 (homepage): Keep tabs
  on your Kerberos server. The plugin takes
  hostname, realm, principal and keytab options, so is appropriately secure.
• check_ldap: Will check ldaps as well as ldap, but you do have to provide a login ID
  and password in plaintext, or just check anonymous bind.

More generally: Roll your own quickly with check_generic (homepage).
This lets you define a command and a set of expectations/thresholds for the return data, thus saving you much of the work involved in writing a plugin. The homepage has thorough documentation and examples.