Lyx doesn't work (can't find cls files)

I know it's an old question, but I just experienced the same problem myself on a fairly recent Mint 17.2 installation.

I used apt-file search article.cls to see which packages have that file - and confirmed that it's present in the texlive-* series of packages. I then did apt-get install texlive - which pulled a few dependencies with it - and the problem was solved.

If you only installed the Lyx Processor and Tex-live then you need to extend the functionality of LyX by installing the listed packages (in bold) for full functionality. They are all available in the Ubuntu Software Center.

Those that are NOT in bold are optional (i think they are self explanatory anyway). When i installed these, all my document classes became available.

For additional document classes (subclasses) and other how tos you can visit the Lyx Wiki here

• chktex: check for typographical errors

• dvipost: display tracked changes in DVI format output

• gnuhtml2latex: import HTML documents

• groff: improved table formatting in plain text exports

• librsvg2-bin, inkscape: use the SVG image format in LyX documents (if your using Inkscape as your graphics editor inr Lyx)

• linuxdoc-tools: export SGML LinuxDoc documents

• mythes-*: use the OpenOffice.org/LibreOffice Thesaurus

• noweb: import noweb files

• rcs: integrated version control

• sgmltools-lite: export SGML DocBook documents

• texlive-xetex, etoolbox: use the XeTeX typesetting system

• wv: import MS Word documents

My new LyX installation showed exactly the same symptoms as the original poster's. I found that there was an old .texmf-var directory in my home directory. Renaming or deleting it, e.g. mv .texmf-var .texmf-var.oldsolved the problem. After that, LyX no longer complains about missing .cls files and compiles documents just fine.

I'm using Ubuntu 12.04, LyX 2.0.7 from https://launchpad.net/~lyx-devel/+archive/release and TeX Live 2012 from https://launchpad.net/~texlive-backports/+archive/ppa.