1. A method for session failover in OS (Operating System) level, executed by a processing unit, comprising: selecting a VM (Virtual Machine) OS to perform a failover when determining that a server OS fails; mapping a memory and a local storage device of the VM OS to physical memory space and physical storage space of a distributed share-memory-and-cloud-storage, which were allocated for the failed server OS via a hypervisor corresponding to the VM OS; and obtaining an OS state of the failed server OS from a distributed cache system via the hypervisor.