LyX/TeX problem: can't find classes

[Will Parsons]

At some point fairly recently (I'm not sure the exact circumstances),
my LyX installation can't produce PDF files anymore because (almost)
all document classes are marked unavailable.  Googling has been no
help - the common recommendations of running (from LyX) "Tools =>
Reconfigure" and (from the command line) "fmtutil-sys --all" have not
solved the problem.

The document that I am currenlty working on uses the "article" class,
and under /usr/local/share/texmf-dist/tex/latex/base there is a file
"article.cls" (among other *.cls files).  I'm at a loss.  Can anyone
shed light on what is wrong?

-- 
Will