How are metal kitchen cabinets attached to wall?

These are all metal except for formica clad doors which were common in the fifties.. I want to remove one section to make headroom there. I removed screws connecting to cabinets on either side. Since there are no screws through the back into the wall, I theorize that it is hung on a flat hook into a stirrup similar to how a wall mount bathroom sink is sometimes hung. But substantial banging on the bottom does not get it too rise up. Does anyone know how they are removed?