Hello,

installing latest stable standalone version on Ubuntu 16.04 x64:
./first-setup.sh --context=current --engine=luatex

fails with:
This is LuaTeX, Version 1.08.0 (TeX Live 2018)  (INITEX)
 system commands enabled.
error in callback:
...018/tex/texmf-context/tex/context/base/mkiv/luat-cod.lua:194: attempt to
call a nil value (upvalue 'isfile')
.
<insert>

<*> ...mf-context/tex/context/base/mkiv/cont-en.mkiv
                                                  dump

Beta on the same machine installs correctly.

Jano