The JES2 job identifier (jobid) is a halfword binary number that is assigned when a job first enters the system. This number is unique within a JES2 system. The job header always contains the original (input system's) jobid.

When a job is transmitted from one system to another, the receiving system attempts to assign the original jobid (from the job header) to the job that is being received. If this number is currently in use on the receiving system, a jobid is assigned as if the job were being read in locally; that is, the job counter is incremented by one until an available number is found. A new jobid is assigned even if a part of the original job is on a receiving system (as may occur for spin data sets). The newly-assigned jobid is not transmitted in the job header.