System upgrade kills Tex

Question

After a system upgrade, when I attempt to use LaTeX, I get the following error from within my compiler (TexMaker). I have no idea what it means. What should I do? (I did not set up TeX on the computer in the first place and don't know how to do that; I know how to open the terminal and do a few simple things but other than that am in over my head.)

Process started

warning: kpathsea: /var/lib/texmf/ls-R: No usable entries in ls-R. warning: kpathsea: See the manual for how to generate ls-R. warning: kpathsea: /usr/share/texmf/ls-R: No usable entries in ls-R. warning: kpathsea: See the manual for how to generate ls-R.

warning: kpathsea: /usr/share/texlive/texmf-dist/ls-R: No usable entries in ls-R. warning: kpathsea: See the manual for how to generate ls-R. kpathsea: Running mktexfmt pdflatex.fmt

warning: kpathsea: /var/lib/texmf/ls-R: No usable entries in ls-R. warning: kpathsea: See the manual for how to generate ls-R.

warning: kpathsea: /usr/share/texmf/ls-R: No usable entries in ls-R. warning: kpathsea: See the manual for how to generate ls-R. warning: kpathsea: /usr/share/texlive/texmf-dist/ls-R: No usable entries in ls-R. warning: kpathsea: See the manual for how to generate ls-R.

tcfmgr: config file `tcfmgr.map' (usually in $TEXMFMAIN/texconfig) not found (ls-R missing?).

Process exited with error(s)

Answer 1

This morning, I experienced the same problem. Thanks to Luis de Sousa's answer (sudo texhash), I am now able to use LaTeX again. I'm posting some screenshots to justify his comment.

Background (TL;DR)

I had TeXLive properly installed on Xubuntu 18.04. The command dpkg -l tex* showed tex-common, texlive-xetex, etc.

Problem

Same as OP's problem.

After sudo texhash

The problem has gone.