https://askubuntu.com/questions/163084/upgrading-ubuntu-chroot-environment
It seems do-release-upgrade is the "best" way to upgrade a chroot. I think I'm struggling to get this to work as my server does not have an internet connection so I must point it to my internal mirror. do-release-upgrade doesn't like my custom sources.list and tries to overwrite it with the official sources and that won't work. (Long story, but I'm able to sneak in a sources.list update on the *host* OS, so it's upgraded to Bionic fine against my internal mirror, but I can't seem to sneak that in the chroot. Maybe I need to up/downgrade the do-release-upgrade version. I had to manually load it in the chroot.) I don't have too much for customizations in my chroot... I could just blow away the chroot and install a fresh Bionic one and restore a few files? Marco
