And pserv.log.2.gz has the actual issue reported, where we see complaints about too many open files. It starts with this:

2014-12-26 21:39:58+0000 [-] Unhandled Error
        Traceback (most recent call last):
          File "/usr/lib/python2.7/dist-packages/twisted/internet/defer.py", line 423, in errback
            self._startRunCallbacks(fail)
          File "/usr/lib/python2.7/dist-packages/twisted/internet/defer.py", line 490, in _startRunCallbacks
            self._runCallbacks()
          File "/usr/lib/python2.7/dist-packages/twisted/internet/defer.py", line 577, in _runCallbacks
            current.result = callback(current.result, *args, **kw)
          File "/usr/lib/python2.7/dist-packages/twisted/internet/defer.py", line 1155, in gotResult
            _inlineCallbacks(r, g, deferred)
        --- <exception caught here> ---
          File "/usr/lib/python2.7/dist-packages/twisted/internet/defer.py", line 1097, in _inlineCallbacks
            result = result.throwExceptionIntoGenerator(g)
          File "/usr/lib/python2.7/dist-packages/twisted/python/failure.py", line 389, in throwExceptionIntoGenerator
            return g.throw(self.type, self.value, self.tb)
          File "/usr/lib/python2.7/dist-packages/provisioningserver/rpc/power.py", line 234, in change_power_state
            'query', context)
          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 148, in wrapper
            return func(*args, **kwargs)
          File "/usr/lib/python2.7/dist-packages/provisioningserver/rpc/power.py", line 111, in perform_power_change
            return action.execute(power_change=power_change, **context)
          File "/usr/lib/python2.7/dist-packages/provisioningserver/power/poweraction.py", line 138, in execute
            template = self.get_template()
          File "/usr/lib/python2.7/dist-packages/provisioningserver/power/poweraction.py", line 86, in get_template
            with open(self.path, "rb") as f:
        exceptions.IOError: [Errno 24] Too many open files: u'/etc/maas/templates/power/sm15k.template'

Nice that it waited for after xmas to start reporting problems.

Immediately after that, it starts to complain:

        Traceback (most recent call last):
          File "/usr/lib/python2.7/threading.py", line 783, in __bootstrap
            
          File "/usr/lib/python2.7/threading.py", line 810, in __bootstrap_inner
            
          File "/usr/lib/python2.7/threading.py", line 763, in run
            
        --- <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/oops/publishers.py", line 38, in result
            
          File "/usr/lib/python2.7/dist-packages/oops_datedir_repo/repository.py", line 133, in publish
            
        exceptions.IOError: [Errno 24] Too many open files: '/var/log/maas/oops/2014-12-26/OOPS-827a2a843c32d4cee606c0c315c99791.tmp'