There are instances when JES2 must be stopped and restarted either by a warm or cold start. For example, redefining the number of systems in a network job environment requires a warm start. A warm start is a restart of JES2 that does not cause the current work and output queues to be rebuilt, but does provide the required changed information to be propagated and used by all necessary components. A warm start is far superior to a cold start.

The definition (or redefinition) of some JES2 facilities and resources require that the JES2 system be totally shut down. JES2 must be restarted with a cold start to allow all component systems to be aware of the changed facilities and resources. A cold start is a JES2 restart that causes all current work and output queues to be lost and rebuilt with new data. The time to restart JES2 in this manner is based on the work in the system and, if not scheduled, causes a disruption in data processing services.