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LaTeX Error: File `…' not found — Package or class not installed

A \usepackage or \documentclass names a file that is not in the TeX installation.

Fix

Check the spelling, install it with tlmgr install <name>, or build in the Overfull Docker image.

Example

Reproduced on TeX Live 2026 by CI · lualatex · corpus/missing-package

Package not installed

Fails: main.tex
\documentclass{article}
\usepackage{fancyplots}
\begin{document}
Hello.
\end{document}
Fixed
\documentclass{article}
\usepackage{pgfplots}
\pgfplotsset{compat=1.18}
\begin{document}
Hello.
\end{document}
What TeX prints in main.log
! LaTeX Error: File `fancyplots.sty' not found.

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

! Emergency stop.
<read *> 
         
l.3 \begin
          {document}
*** (cannot \read from terminal in nonstop modes)

!  ==> Fatal error occurred, no output PDF file produced!