A technique for shutting down virtual machines in a computer system which comprises a real computer and a virtual machine operating system. The virtual machine operating system comprises a common base portion and a plurality of virtual machines sharing the common base portion. According to one feature of the present invention, the common base portion receives a shutdown signal from the real computer. The shutdown signal specifies a time period for shutdown of the common base portion or the virtual machine operating system. Next, the common base portion determines a time period for shutdown of the virtual machines by subtracting a time required to shutdown the common base portion from the specified time period. Next, the common base portion sends requests to the virtual machines to shut down in an orderly manner within the time period determined for shutdown of the virtual machines. The common base portion determines when and if each of the virtual machines shuts down in an orderly manner. If all of the virtual machines shut down in an orderly maimer before the time period determined for shutdown of the virtual machines lapses, before lapse of the time specified in the shutdown signal from the real computer, the common base portion shuts itself down. However, if all of the virtual machines do not shut down in an orderly manner before the time period determined for shutdown of the virtual machines lapses, upon lapse of said time period determined for shutdown of the virtual machines, the common base portion shuts itself down. The shutting down of the common base portion disrupts any of the virtual machines that did not shut down in an orderly manner. The shutdown can also be initiated by a user at or an application running on one of the virtual machines.