The best material to use under linoleum flooring is a plywood underlayment. This underlayment will help level out your floor so you can apply your linoleum flooring easily. You can also use other types of underlayment such as backer board or cork underlayment.  Since the underlayment for linoleum flooring raises the level of the floor, you must make sure that there is enough space to put it under or around cabinets and appliances.