Thank you for taking the time to report this issue and help to improve Ubuntu.
> I append "nosplash" in the boot parameters, but the plymouth theme is still shown.
Why would you use "nosplash" instead of omitting "splash"?
There is a bug in plymouth's kernel commandline parsing here, it doesn't respect word boundaries when looking for 'splash'; but I don't think "nosplash" is a documented option, either.
Thank you for taking the time to report this issue and help to improve Ubuntu.
> I append "nosplash" in the boot parameters, but the plymouth theme is still shown.
Why would you use "nosplash" instead of omitting "splash"?
There is a bug in plymouth's kernel commandline parsing here, it doesn't respect word boundaries when looking for 'splash'; but I don't think "nosplash" is a documented option, either.