TeX Live issue after update - `fmtutil.cnf` not found

The new texlive-core package requires user-intervention when updating. Running sudo pacdiff (this replaces existing files with the new .pacnew files) followed by sudo fmtutil-sys --all should fix it.

For more complete instructions, see: https://www.archlinux.org/news/texlive-2013-update-may-require-user-intervention/

I had the same problem. I was able to solve it with moving all texlive-related .pacnew-files into their new locations. After that, the following steps solved the problem for me:

mv ~/.texlive /tmp
fmutil -all
sudo fmutil -all
sudo texhash