The light fixture is hanging from the outside ceiling of my doorstep and looks like a postlight figure. It is old and rusty. There are two screw-like knobs on top of the fixture. I’ve tried screwing or pulling them. But they just won’t budge. Any idea how to open the casing?

try a small socket the same size or a nut driver
if the fixture is that rusty it should be replaced
You will have to put some rust killer on those screws and they should screw off
WD-40…..100% of the time, it works everytime!
spray some wd-40 on them that should loosen the rust up enough to get them unscrewed.
you may also want to try using a wrench or a pair of plyers to turn the knobs.
I am having a problem with getting the cover off the flourescent light fixture in my kitchen, it is so agravating! It is nothing fancy, just a simple tube fixture…can’t see how to do it and I am usually pretty handy.
if it is that rusty buy a new one
the two screws are they like holding the fixture , check on top , does this light have a pointed top
use the wd 40 or buy a new one , i would buy a new one to heck with the fuss