Let the technician boot the box and tell him to escape to the boot prompt. When he will be done, he just need to unset those variables with the following command -- unset kern.maxdsiz; and unset kern.dfldsiz. After that, he will just have to type 'boot' and that's all. I hope that this will work for him ;-)

如果在 loader.conf 裡面的參數設定錯了，可以在開機時 escape 到 boot prompt，然後使用 unset 把 loader.conf 裡設定的東西暫時移除，以便正常開機。