Comment 26 for bug 1551854

Ok, so investigation shows that:

 - LXD bind-mounts all that stuff, it doesn't have a choice as it's not privileged enough to mount things itself
 - mountall fails to run if its "optional" filesystems fail to mount (because that makes a lot of sense...)
 - systemd sets up the host filesystems, on a clean boot they all seem fine
 - "something" apparently remounts debugfs ro sometimes, this breaks containers
 - "something" apparently makes the /proc/sys/fs/binfmt_misc autofs go nuts (loop of symlinks) which also breaks containers

We could try to teach mountall to do the right thing with optional mount and ignore their failures, however we'd need to SRU that to trusty and precise and then nag other distros in doing the same (centos, oracle, rhel, ...) before we can get rid of our workaround.

As a clean Xenial system does work properly, I think it would be best to figure out what's messing with debugfs and binfmt_misc post-boot and fix whatever it is to stop doing that.

Would be useful if the bug reporters could document exactly what they did on their system between the time it worked fine and the time it stopped working so we can figure out what's messing with those mounts.