I peeled up as much of old vinyl as I could. Then I bought the "instant cancer & brain damage" stuff from the Depot in the paint thinner aisle. The can was gold colored and was 1 gallon IIRC. It goes on like grape jelly. Let it soak a bit then get on your knees and scrape. It goes quicker the longer the stuff sits.
If your floor is over wood, put down 1/8" wood on top, don't bother stripping old.
Warning: Shut off pilot lights (including water heater) gas fireplace and stove/oven. Put a fan in the window blowing out. Get a chemical air filter with mask. These fumes are not as potent as I thought, but....
Would I repeat? yes, I did already. It eats up kneepads. I think I used paint thinner or similar to neutralize the acidic effect of stripper. Read the can. If you glue down new floor to the stripper itself, you WILL have air pockets. DAMHIKT.
Good luck, Tom