JES2
The job entry subsystem: the part of z/OS that queues jobs, decides when they run, and collects their output.
Also written JES, JES3, job entry subsystem
JES2 is the job entry subsystem. It manages the whole lifecycle of batch work: reading in submitted JCL, holding jobs in a queue, choosing what runs when, and capturing the output on the spool afterwards.
When you submit a job, JES2 takes it, checks the JCL, gives it a job number and queues it. Whether it starts immediately depends on its class and priority, and on what else is competing. Once it finishes, JES2 holds its output until you or a purge process disposes of it.
There is a second variant, JES3, used at a minority of sites, which does the same job with different scheduling behaviour. JES2 is much more common, and the two are similar enough that the concepts transfer.
Most of your contact with it is through SDSF, which is essentially a window onto the JES queues and spool. The system commands that display and control jobs are JES commands too, which is why the prefixes on those commands look unusual at first.
Related terms
- JobA unit of batch work submitted to the system, made up of one or more steps that run in order.
- SpoolThe system-managed holding area where job output waits to be read, printed or purged.
- SDSFThe tool for looking at what jobs are running, what has finished, and what output they produced.
- SubmitHanding JCL to the system to be run, which queues it as a job and gives it a job number.
- Job classA single-character label on a job that tells the system what kind of work it is and how to schedule it.