You can order the permit here : www.environnement.public.lu/guichet_virtuel/escalade/index.html . If you come from far away, you only get 1 day permits.( You might try to come without as there are almost no controls. This is not encouraged!)
This information is a public crowdsourcing effort between the Access Fund,
and Mountain Project. You should confirm closures, restrictions, and/or related dates.