Comment 2 for bug 1840658

Additional information:
- the container is a "VPS" provided by a popular local hosting company Interneto Vizija (https://iv.lt)
- they have their own patched 2.6.32-042stab138.1 kernel that I have no capability of upgrading
- the upgrade process shows a fancy ncurses warning that libc6 requires a newer kernel version (3.2 or later), but provides no option to abort the upgrade at that point

Recovering from the failed upgrade appears to be simple:
- change bionic back to xenial in /etc/apt/sources.list
- apt install locales/xenial libc6-dev/xenial libc6-dbg/xenial libc-dev-bin/xenial