A truck bed liner for a truck bed having a bed floor and two opposing bed walls is provided. The bed liner includes a bed floor configured to be disposed along the floor of the truck bed. The bed liner also includes two opposing side walls which conform the truck bed side walls, and a third wall attached to the side walls near the front of the truck bed. Each of the side walls includes a rail integrally formed with a corresponding side wall, and running the length of the side wall. Each of the rails includes a plurality of threaded holes which can be used to attach cargo items using threaded fasteners. Each of the holes also includes a cleanout, which provides for removal of dirt and debris from the holes, and facilitates the use of a lockable threaded fastener to more securely attach cargo items to the bed liner.