When trying to compile the following MWE using pdflatex:

 Test Test

I get the following error message:

jbroedel@t450s:~/Dropbox/LatexTest$ pdflatex test.tex 
This is pdfTeX, Version 3.14159265-2.6-1.40.21 (TeX Live 2020/Debian) (preloaded format=pdflatex)
 restricted \write18 enabled.
entering extended mode
LaTeX2e <2020-02-02> patch level 5
L3 programming layer <2020-06-18>
Document Class: article 2019/12/20 v1.4l Standard LaTeX document class

! LaTeX Error: File `l3backend-pdfmode.def' not found.

Type X to quit or <RETURN> to proceed,
or enter new name. (Default extension: def)

Enter file name:

The file l3backend-pdfmode.def is not present. I am using the Debian packages of TexLive, which does now by default use some parts of l3backend:

ii  texlive-base   2020.20200925-1 all          TeX Live: Essential programs and files

Did somebody experience a similar problem? If this turns out not to be my fault, I will file a bug report, however, would be happy for a workaround solution.

  • Is l3backend package installed?
    – Tanvir
    Commented Oct 9, 2020 at 15:13
  • l3backend is by now part of texlive-latex-base. So, yes, it is installed. There is no extra package l3backend any more, as far as I could find out.
    – jbroedel
    Commented Oct 9, 2020 at 15:17
  • The MWE works in my machine with texlive 2020. Are you using two different versions of texlive ? The l3backend package is available on CTAN.
    – Tanvir
    Commented Oct 9, 2020 at 15:29
  • something got out of sync. You seem to have a new l3backend version (where pdfmode has been splitted into pdftex and luatex) and an older format/expl3 which still looks for pdfmode. Try to recreate the formats. Commented Oct 9, 2020 at 15:31
  • I recreatet the formats several times using Debians reconfigure mechanism. No improvement. I can see that I do have a newer version as the folder /usr/share/texlive/texmf-dist/tex/latex/l3backend does contain the two splitted .def files. I suppose Debian TexLive maintainers have packaged nonmatching versions - could this be the reason?
    – jbroedel
    Commented Oct 9, 2020 at 15:37

1 Answer 1


Now pdflatex from TexLive runs flawless with the Debian TexLive packages.

The problem was the (not systemwide) folder ~/texlive2020 containing an old .fmt file. Following the usual latex strategy, this would be used preferrably over the newly generated systemwide format files from installing a new TeXLive version. Why this version of pdflatex.fmt in a subfolder of my home folder has not been found by kpsewhich (see comments on my question) is not clear to me, but can for sure be explained.

Punchline: the old installation was not completely removed for all users, and interfered with the new (and fresh) installation.

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