Dear developer,

Plymouth ships text themes, and graphical themes in a separate
plymouth-themes package, which have many more dependencies.

Installing only plymouth (without plymouth-themes) and selecting the
tribar theme currently makes update-initramfs fail because it can't find
the file /etc/fonts/fonts.conf (shipped with fontconfig-config), which
tribar doesn't need at all, since it's a actually a text theme
(correctly shipped with the main plymouth package, and not in the
plymouth-themes package).

This probably stayed off the radar since plymouth is rarely installed on
a system without a desktop (and thus, no fonts). That's why the
probability to mess up the initramfs is quite low, but it's nevertheless
a possibility.

This can be easily fixed by adding tribar to the dependencies test in
the initramfs hook (see provided patch).

I tested it in a VM on a standard headless system (bullseye), with and
without encrypted root; the text prompts for entering the passphrase and
reporting success or failure are correctly displayed.

Regards,