Attempting to upgrade a fully updated 14.04.3 system to Xenial using the do-release-upgrade tool.
The upgrade proceeds until it attempts to install fontconfig. This fails and causes a cascading set of failures for 160+ more packages resulting in a system that boots, and has console access, but no Unity, and other things that either fail to work or only work halfway.
Attempts after the failed upgrade to fix the issues via "apt-get -f install" fail with the same errors as seen during the upgrade.
Here's the apt term log showing the errors, starting with fontconfig:
http://paste.ubuntu.com/14852379/
And here's the contents of fontconfig.log as suggested by trying to manually install fontconfig vai "apt-get install fontconfig"
/usr/share/fonts: caching, new cache contents: 0 fonts, 4 dirs
/usr/share/fonts/X11: caching, new cache contents: 0 fonts, 4 dirs
/usr/share/fonts/X11/Type1: caching, new cache contents: 9 fonts, 0 dirs
/usr/share/fonts/X11/encodings: caching, new cache contents: 0 fonts, 1 dirs
/usr/share/fonts/X11/encodings/large: caching, new cache contents: 0 fonts, 0 dirs
/usr/share/fonts/X11/misc: caching, new cache contents: 59 fonts, 0 dirs
/usr/share/fonts/X11/util: caching, new cache contents: 0 fonts, 0 dirs
/usr/share/fonts/cmap: caching, new cache contents: 0 fonts, 5 dirs
/usr/share/fonts/cmap/adobe-cns1: caching, new cache contents: 0 fonts, 0 dirs
/usr/share/fonts/cmap/adobe-gb1: caching, new cache contents: 0 fonts, 0 dirs
/usr/share/fonts/cmap/adobe-japan1: caching, new cache contents: 0 fonts, 0 dirs
/usr/share/fonts/cmap/adobe-japan2: caching, new cache contents: 0 fonts, 0 dirs
/usr/share/fonts/cmap/adobe-korea1: caching, new cache contents: 0 fonts, 0 dirs
/usr/share/fonts/truetype: caching, new cache contents: 1 fonts, 19 dirs
/usr/share/fonts/truetype/abyssinica: caching, new cache contents: 1 fonts, 0 dirs
/usr/share/fonts/truetype/dejavu: caching, new cache contents: 6 fonts, 0 dirs
/usr/share/fonts/truetype/droid: caching, new cache contents: 18 fonts, 0 dirs
/usr/share/fonts/truetype/freefont: caching, new cache contents: 12 fonts, 0 dirs
/usr/share/fonts/truetype/kacst: caching, new cache contents: 15 fonts, 0 dirs
/usr/share/fonts/truetype/kacst-one: caching, new cache contents: 2 fonts, 0 dirs
/usr/share/fonts/truetype/lao: caching, new cache contents: 1 fonts, 0 dirs
/usr/share/fonts/truetype/liberation: caching, new cache contents: 16 fonts, 0 dirs
/usr/share/fonts/truetype/nanum: caching, new cache contents: 6 fonts, 0 dirs
/usr/share/fonts/truetype/openoffice: caching, new cache contents: 1 fonts, 0 dirs
/usr/share/fonts/truetype/padauk: caching, new cache contents: 4 fonts, 0 dirs
/usr/share/fonts/truetype/sinhala: caching, new cache contents: 1 fonts, 0 dirs
/usr/share/fonts/truetype/takao-gothic: caching, new cache contents: 1 fonts, 0 dirs
/usr/share/fonts/truetype/tibetan-machine: caching, new cache contents: 1 fonts, 0 dirs
/usr/share/fonts/truetype/tlwg: caching, new cache contents: 54 fonts, 0 dirs
/usr/share/fonts/truetype/ttf-indic-fonts-core: caching, new cache contents: 17 fonts, 0 dirs
/usr/share/fonts/truetype/ttf-khmeros-core: caching, new cache contents: 2 fonts, 0 dirs
/usr/share/fonts/truetype/ttf-punjabi-fonts: caching, new cache contents: 2 fonts, 0 dirs
/usr/share/fonts/truetype/ubuntu-font-family: caching, new cache contents: 13 fonts, 0 dirs
/usr/share/fonts/type1: caching, new cache contents: 0 fonts, 2 dirs
/usr/share/fonts/type1/gsfonts: caching, new cache contents: 35 fonts, 0 dirs
/usr/share/fonts/type1/mathml: caching, new cache contents: 1 fonts, 0 dirs
/usr/local/share/fonts: caching, new cache contents: 0 fonts, 0 dirs
/.local/share/fonts: skipping, no such directory
Re-scanning /usr/share/fonts: fc-cache: symbol lookup error: fc-cache: undefined symbol: FcDirCacheRescan
Status changed to 'Confirmed' because the bug affects multiple users.