! LaTeX Error: The font size command \normalsize is not defined:

개요

root@localhost:/data# cat a.tex
\begin{document}
Hello world!
\end{document}
root@localhost:/data# pdflatex -halt-on-error a.tex
This is pdfTeX, Version 3.14159265-2.6-1.40.21 (TeX Live 2020) (preloaded format=pdflatex)
 restricted \write18 enabled.
entering extended mode
(./a.tex
LaTeX2e <2020-10-01> patch level 4
L3 programming layer <2021-02-18>
(/opt/texlive/texdir/texmf-dist/tex/latex/l3backend/l3backend-pdftex.def)
(./a.aux)

! LaTeX Error: The font size command \normalsize is not defined:
               there is probably something wrong with the class file.

See the LaTeX manual or LaTeX Companion for explanation.
Type  H <return>  for immediate help.
 ...                                              
                                                  
l.1 \begin{document}
                    
!  ==> Fatal error occurred, no output PDF file produced!
Transcript written on a.log.