/usr/bin/m-tx is in texlive-music 2017.20180305-2.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/bin/../share/texlive/texmf-dist/scripts/m-tx/m-tx.lua
/usr/bin/../share/texlive/texmf-dist/scripts/m-tx/m-tx.lua