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debugging

Plugin Debugging

Debugging plugins can sometimes be complicated since there are so many classes, which are tied together in an implicit way. I have collected some frequent questions about debugging.

single: verbose; traceback

An uncaught exception makes the plugin return UNKNOWN. Where is the cause?

When your plugin raises an exception, you may get very little output. Example:

$ check_users.py
USERS UNKNOWN: RuntimeError: error

Set the verbose parameter of :py~nagiosplugin.check.Check.main to some value greater than zero and you will get the full traceback:

$ check_users.py -v
USERS UNKNOWN: RuntimeError: error
Traceback (most recent call last):
  File "nagiosplugin/runtime.py", line 38, in wrapper
    return func(*args, **kwds)
  File "nagiosplugin/examples/check_users.py", line 104, in main
    check.main(args.verbose, args.timeout)
  File "nagiosplugin/check.py", line 110, in main
    runtime.execute(self, verbose, timeout)
  File "nagiosplugin/runtime.py", line 118, in execute
    with_timeout(self.timeout, self.run, check)
  File "nagiosplugin/platform/posix.py", line 19, in with_timeout
    func(*args, **kwargs)
  File "nagiosplugin/runtime.py", line 107, in run
    check()
  File "nagiosplugin/check.py", line 95, in __call__
    self._evaluate_resource(resource)
  File "nagiosplugin/check.py", line 73, in _evaluate_resource
    metrics = resource.probe()
  File "nagiosplugin/examples/check_users.py", line 57, in probe
    self.users = self.list_users()
  File "nagiosplugin/examples/check_users.py", line 34, in list_users
    raise RuntimeError('error')
RuntimeError: error

A Check constructor dies with "cannot add type <...>"

When you see the following exception raised from :py~nagiosplugin.check.Check (or Check.add()):

UNKNOWN: TypeError: ("cannot add type <class '__main__.Users'> to check", <__main__.Users object at 0x7f0c64f73f90>)

chances are high that you are trying to add an object that is not an instance from Resource, Context, Summary, or Results or its subclasses. A common error is to base a resource class on object instead of :py~nagiosplugin.resource.Resource.

pdb

I'm trying to use pdb but I get a timeout after 10s

When using an interactive debugger like pdb on plugins, you may experience that your debugging session is aborted with a timeout after 10 seconds. Just set the timeout parameter in :py~nagiosplugin.check.Check.main to 0 to avoid this.