My first gut reaction was, "Why would anybody want to install Unity?" But I
realize that in a sense I'm trolling and to each his own preferences... De
gustibus non est disputandum...
Since I don't use Unity, I can't offer specific help, but let me make a
suggestion that hopefully will prove helpful. Try installing Trisquel with a
GUI first, then follow the directions for installing Unity. This approach
serves two purposes. First, you make sure X is working (troubleshooting an
incompletely installed or incorrectly configured X can be a real pain).
Second, package dependencies don't always make sense. Earlier this morning I
completely removed X from my laptop (xorg-xserver*, etc. -- because, as I
said before, troubleshooting is a pain, and reinstalling all that stuff
turned out to be easier). I noticed that removing X took out a bunch of stuff
that depended on it, as expected, but didn't take out everything that should
depend on it. In particular, GHex, Code::Blocks, Calibre, gschem, and other
GUI apps were still installed. These should depend on X (or depend on things
that depend on X), shouldn't they? If there are missing links in the
dependency chains, then you might not be pulling in everything actually
needed to run Unity.
tl;dr -- My suggestion is try installing a full regular Trisquel with the
standard GUI, then adding Unity after everything else is working...
