When using ConTeXt from a fresh install (4.1 MATE), we get the error:

mtxrun | unknown script 'context.lua' or 'mtx-context.lua'

This can be fixed by setting the texmf path. The lua files above are found with:

locate mtx-context.lua
/usr/share/texmf-dist/scripts/context/lua/mtx-context.lua

The issue seems to be fixed by

export TEXMF=/usr/share/texmf-dist

I'm not sure this is the correct solution, but the package maintainer probably does.

This was inspired by: https://dilawarnotes.wordpress.com/2016/02/20/fix-unknown-script-context-lua-or-mtx-context-lua/