1. A method of providing policy-based operating system services in an operating system on a computing system, the computing system comprising at least one compute node, the compute node comprising an operating system, the operating system further comprising a kernel and a plurality of operating system services of a service type, the operating system including computer program instructions capable of carrying out the method, the method comprising: establishing, on the compute node, a kernel policy specifying one of the operating system services of the service type for use in the operating system in dependence upon the hardware and software environment managed by the operating system; and retrieving the specified operating system service from the kernel policy in dependence upon the specified service type; determining, by the kernel, whether the kernel is able to access the specified operating system service; and accessing, by the kernel, the specified operating system service if the kernel is able to access the specified operating system service; and executing, by the compute node, computer program instructions implementing a default operating system service of the service type if the kernel is unable to access the specified operating system service.