Debugging Nagios plugins

Wolfgang Wagner has written this really good how-to about debugging Nagios plugins. It can be a pain to find out when you add or write a new check. The solution is to let a script (capture.pl) that takes care of redirecting STDOUT and STDERR to a logfile make the call.

This is how it works

  1. Download capture.pl
  2. Redefine the check command so that catpture.pl is called and passed the rest of the check
  3. get the log in /tmp/captured-plugins.log

Syntax

So this is how the check I wanted to debug was looking like: 

  # 'check_alive_by_ssh_login' command definition
  define command{
      command_name    check_alive_by_ssh_login
      command_line    $USER1$/capture_plugin.pl /usr/bin/ssh -q -p $ARG1$ $HOSTADDRESS$
      }

And the output looked like this: 

  2009-7-24 11:14:4 ------ debugging
  cmd=[/usr/bin/ssh '-q' '-p' '220' 'xxx.xxx.xxx.xxx']
  output=[Permission denied, please try again.
  Permission denied (publickey,password,keyboard-interactive).
  ]

… meaning basically there was something wrong with the ssh public key for that host. This tool has already saved me hours of testing so I'm happy to link it.

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