Comment 1 for bug 1492691

Some more findings:
1. I think it's apparently that the hang is due to upstart lost tracking on the job's pid.
2. Before the hang occurred, there is a package upgrade. And due to there is libc upgrade (upstart depends on libc), it tries to restart the upstart via "telinit u". But don't know why the restart seems have problem to be finished; we can see there is an additional init process keeping running, where I think it should be a transient status. I guess the expected behavior is that the older init should be replaced by the new init after all things get migrated to the new init. but it seems it's not finished in time and is kept in an intermediate status.
$ ps -ef | grep init
root 1 0 0 Oct14 ? 00:00:05 /sbin/init
root 6647 1 0 Oct15 ? 00:00:00 /sbin/init

$ ps -ef | grep upstart
root 315 1 0 Oct14 ? 00:00:00 upstart-udev-bridge --daemon
root 526 1 0 Oct14 ? 00:00:00 upstart-socket-bridge --daemon
root 530 1 0 Oct14 ? 00:00:00 upstart-file-bridge --daemon
stack 2154 19493 0 02:57 pts/25 00:00:00 grep upstart
root 6781 1 0 Oct15 ? 00:00:00 upstart-udev-bridge --daemon
root 8188 1 0 Oct15 ? 00:00:00 upstart-file-bridge --daemon
root 8191 1 0 Oct15 ? 00:00:00 upstart-socket-bridge --daemon

Need some upstart experts help to dig further. Thanks.