Comment 2 for bug 1484698

Using the chmod hack, your traceback will look like this:

==> /var/log/maas/clusterd.log <==
2015-10-15 17:28:43-0400 [-] Unhandled failure dispatching AMP command. This is probably a bug. Please ensure that this error is handled within application code or declared in the signature of the RemoveHostMaps command. [maas-trusty-testbench:pid=639:cmd=RemoveHostMaps:ask=7]
 Traceback (most recent call last):
   File "/usr/lib/python2.7/threading.py", line 783, in __bootstrap
     self.__bootstrap_inner()
   File "/usr/lib/python2.7/threading.py", line 810, in __bootstrap_inner
     self.run()
   File "/usr/lib/python2.7/threading.py", line 763, in run
     self.__target(*self.__args, **self.__kwargs)
 --- <exception caught here> ---
   File "/usr/lib/python2.7/dist-packages/twisted/python/threadpool.py", line 191, in _worker
     result = context.call(ctx, function, *args, **kwargs)
   File "/usr/lib/python2.7/dist-packages/twisted/python/context.py", line 118, in callWithContext
     return self.currentContext().callWithContext(ctx, func, *args, **kw)
   File "/usr/lib/python2.7/dist-packages/twisted/python/context.py", line 81, in callWithContext
     return func(*args,**kw)
   File "/usr/lib/python2.7/dist-packages/provisioningserver/utils/twisted.py", line 200, in wrapper
     return func(*args, **kwargs)
   File "/usr/lib/python2.7/dist-packages/provisioningserver/rpc/dhcp.py", line 224, in remove_host_maps
     omshell.remove(mac_address)
   File "/usr/lib/python2.7/dist-packages/provisioningserver/dhcp/omshell.py", line 225, in remove
     returncode, output = self._run(stdin)
   File "/usr/lib/python2.7/dist-packages/provisioningserver/dhcp/omshell.py", line 133, in _run
     proc = Popen(self.command, stdin=PIPE, stdout=PIPE)
   File "/usr/lib/python2.7/subprocess.py", line 710, in __init__
     errread, errwrite)
   File "/usr/lib/python2.7/subprocess.py", line 1327, in _execute_child
     raise child_exception
 exceptions.OSError: [Errno 13] Permission denied

Most likely, while experimenting a real failure, you'll see a different exception, but on the same line.