Conclusion thus far: What I am seeing might be a new breakage of yubikey-luks in U18.10/Cosmic.
I dug up an older Ubuntu system (U16.04.3 LTS) that is known-working with Yubikey LUKS + Plymouth, and `/conf/conf.d/cryptroot` is present in initramfs. Contents is one line, a target specification for the root FS. The line referencing it in `/scripts/local-top/yubikey-luks` looks substantially similar to the one in U18.10 / Cosmic. Digging through various versions of cryptsetup imported from upstream (Debian), I see that between ubuntu/bionic and ubuntu/cosmic, generation of `/conf/conf.d/cryptroot` seems to have been retired. Specifically, as part of refactoring at: debian/changelog cryptsetup (2:2.0.3-2) unstable; urgency=medium [ Guilhem Moulin ] * debian/initramfs/*-hook: complete refactoring. Common functions are now in /lib/cryptsetup/functions (source-able from shell scripts). (Closes: #784881.) https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=784881 … subsequent to which, debian/initramfs/cryptroot-hook add_device() (the function which was responsible for constructing `/conf/conf.d/cryptroot`) disappears. Also of note: I fully removed yubikey-luks (`apt-get --purge remove yubikey-luks`), and only the first of the two cryptroot errors I mentioned above has disappeared. -- Looks like the "line 218" one is unrelated to yubikey-luks. ** Bug watch added: Debian Bug tracker #784881 https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=784881 -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1619921 Title: Password Prompt for yubikey not showing in Plymouth To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/yubikey-luks/+bug/1619921/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs