This was automatically done for me whilst upgrading from 14.04 LTS to 16.04 LTS.
ProblemType: Package
DistroRelease: Ubuntu 16.04
Package: plymouth 0.9.2-3ubuntu13.1
ProcVersionSignature: Ubuntu 3.13.0-95.142-generic 3.13.11-ckt39
Uname: Linux 3.13.0-95-generic x86_64
ApportVersion: 2.20.1-0ubuntu2.1
Architecture: amd64
Date: Mon Oct 3 07:58:46 2016
DefaultPlymouth: Error: command ['readlink', '/etc/alternatives/default.plymouth'] failed with exit code 1:
ErrorMessage: subprocess installed post-installation script returned error exit status 1
InstallationDate: Installed on 2012-01-17 (1720 days ago)
InstallationMedia: Ubuntu-Server 10.04.3 LTS "Lucid Lynx" - Release amd64 (20110719.2)
MachineType: Hewlett-Packard HP Compaq dc5750 Small Form Factor
ProcCmdLine: BOOT_IMAGE=/boot/vmlinuz-3.13.0-95-generic root=UUID=0563ecb7-db49-44da-aa61-59f5fd4dfdc9 ro quiet
ProcFB: 0 radeondrmfb
ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-3.13.0-95-generic root=UUID=0563ecb7-db49-44da-aa61-59f5fd4dfdc9 ro quiet
RelatedPackageVersions:
dpkg 1.18.4ubuntu1.1
apt 1.2.12~ubuntu16.04.1
SourcePackage: plymouth
TextPlymouth: /lib/plymouth/themes/ubuntu-text/ubuntu-text.plymouth
Title: package plymouth 0.9.2-3ubuntu13.1 failed to install/upgrade: subprocess installed post-installation script returned error exit status 1
UpgradeStatus: Upgraded to xenial on 2016-10-03 (0 days ago)
dmi.bios.date: 01/25/2007
dmi.bios.vendor: Hewlett-Packard
dmi.bios.version: 786E3 v02.10
dmi.board.name: 0A64h
dmi.board.vendor: Hewlett-Packard
dmi.chassis.asset.tag: AUD82704CT
dmi.chassis.type: 4
dmi.chassis.vendor: Hewlett-Packard
dmi.modalias: dmi:bvnHewlett-Packard:bvr786E3v02.10:bd01/25/2007:svnHewlett-Packard:pnHPCompaqdc5750SmallFormFactor:pvr:rvnHewlett-Packard:rn0A64h:rvr:cvnHewlett-Packard:ct4:cvr:
dmi.product.name: HP Compaq dc5750 Small Form Factor
dmi.sys.vendor: Hewlett-Packard
Status changed to 'Confirmed' because the bug affects multiple users.