Comment 20 for bug 595648

Have a look at probably simpler solution provided here:
https://bugs.launchpad.net/cryptsetup/+bug/556372

The solution is to install plymouth-dummy package and remove the standard one. Then everything works fine as earlier.
This is fully based on https://bugs.launchpad.net/cryptsetup/+bug/556372/comments/78
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Oliver Joos (oliver-joos) wrote on 2012-03-25: #78

Ok then, here is the ready-to-install plymouth-dummy_1.0_all.deb! It's an empty package but allows to remove plymouth while keeping the packages that have wrong dependencies to plymouth.

To workaround this (WontFix??) bug and remove plymouth just execute 2 commands in a Terminal:
  sudo dpkg -i plymouth-dummy_1.0_all.deb
  sudo apt-get remove plymouth

Advanced users can build plymouth-dummy_1.0_all.deb themselves: see comment 16
Many thanks to Christian Kujau!
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I've tested it on 12.04 LTS