Well, with a bit of help from Chris and Sebastien, I found the possible culprit: myself. I must have tried to customise GDM, and this results in a /var/lib/gdm with, er, GDM configuration options.
So. I shot myself. Closing as INVALID, user error. ** Package changed: initramfs-tools (Ubuntu) => gdm (Ubuntu) ** Changed in: gdm (Ubuntu) Status: New => Invalid -- package gdm 2.28.0-0ubuntu8 failed to install/upgrade: subprocess installed post-installation script returned error exit status 1 https://bugs.launchpad.net/bugs/438789 You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs