Comment 3 for bug 1284164

This isn't really a bug with Upstart since it appears the problem is that bamfdaemon is spamming dbus somehow. Upstart is simply logging the output.

That said, there is an outstanding merge proposal to have the session logrotate job run periodically which would have avoided so much disk space being taken (although it would also potentially have caused the bamfdaemon problem from being noticed):

https://code.launchpad.net/~jamesodhunt/ubuntu/trusty/upstart/periodic-logrotate

Once approved (and an FFE raised if necessary), this will resolve the Upstart aspect of this issue.