Linux Shutdown Logging

Linux is pretty solid generally, but there are times when it fails to shutdown cleanly, or takes forever to do so, and this is almost always some process getting stuck or failing to shutdown when asked to do so. 

Luckily, debugging this is easy: 

journalctl -b -1 -ex

Will show you the logs before it last rebooted. If you still don't see it, then omit the -ex to get the whole startup/shutdown from the last boot and page through it. 

You will eventually see some failures, when a service failed to stop, or a disk failed to unmount, or even some hardware failed to respond. Focus in on that and you have your solution.