Undefined control sequence using pdfx and Lualatex

Question

Compiling a simple example on PDF/A with Lualatex returns the following error:

! Undefined control sequence.
l.660  \ifnum\shellescape

Or, for a PDF/X:

! Undefined control sequence.
l.333  \pdfobjcompresslevel
                         =0 \relax

How can I compile a document under Lualatex with PDFx compliance?

Example code, running on Texlive 2018:

\documentclass{scrbook}
\usepackage[x-4]{pdfx}

\begin{document}
\chapter{Intro}
Things and stuff.
\end{document}

Answer 1

The package pdfx requires luatex85. It is only required for Luatex, so they don't get pulled in by the package manager. Installing texlive-luatex85 fixes the problem. No need to modify the tex.

(The documentation claims pdftexcmds from texlive-oberdiek can also be used, but it doesn't work on my box, I need luatex85 or both.)