pdflatex on TL2020 complains about not finding l3backend-pdfmode.def

[AC]

Thank you! Your first suggestion resolved it (more below).

On September 28, 2020 4:19:52 PM EDT, David Carlisle <d.p.carlisle at gmail.com> wrote:
>the backed file is now l3backend-pdfmode.def (or l3backend-luatex.def)
>the
>pdfmode.def file is no longer used.

Just curiosity: was there a typo above? You write that the backend file is l3backend-pdfmode.def, but that's exactly the file I was missing..

>If it is being referenced then either your formats didn't get remade
>fmtutil-sys --all
>should remake them

This did indeed work: after removing 'l3backend-pdfmode.def' (which I'd copied to <texlive>/2020/texmf-dist/tex/latex/backends/ manually from 2019) and running

fmtutil-sys --all

pdflatex is back in action.

>or you have a local format that is masking the ones made by the system
>update
>check with
>kpsewhich --engine=pdftex --all pdflatex.fmt
>that you don't have an old local pdflatex format in your input path
>
>
>
>
>On Mon, 28 Sep 2020 at 21:10, AC <achirvasub at gmail.com> wrote:
>
>> I have two machines running vanilla-installed TL, migrated[0] from
>2019 on
>> both.
>>
>> I have compiled with pdflatex on both just fine.
>>
>> After a recent upgrade, running 'pdflatex' (i.e. the command pdflatex
>> <tex-file> in a linux terminal) on one of them (henceforth BAD)
>results in
>> the error that l3backend-pdfmode.def cannot be found.
>>
>> On the other one (henceforth GOOD) everything works fine, even though
>> l3backend-pdfmode.def is not present there either.
>>
>> On both machines I have l3backend-pdfmode.def in
>> <path-to-texlive>/2019/texmf-dist/tex/latex/l3backend/
>>
>> but GOOD runs without issues without that file in the analogous 2020
>> folder, whereas on BAD I have to copy that file to
>>
>> <path-to-texlive>/2020/texmf-dist/tex/latex/l3backend/
>>
>> to fix the problem.
>>
>> ---
>>
>> References:
>>
>> [0] https://tug.org/texlive/upgrade.html
>>
>>