A bad job dies a thousand deaths; a good job dies but one. Some jobs are difficult to end. Communication jobs that have gone awry are particularly prone to not ending, even when you've executed an End Job (ENDJOB) command with *IMMED specified for the OPTION parameter. The End Job Abnormal (ENDJOBABN) command can help kill those cowardly jobs.
ENDJOBABN is used to end a job that will not end through normal means. The parameters on this command are job name, user, and job number. The ENDJOBABN command requires that an ENDJOB OPTION(*IMMED) has already been run against the job you are trying to end. It also requires a lapse of 10 minutes for the ENDJOB command to have effect. Once those conditions are met, you can then run ENDJOBABN.
The only consideration for the ENDJOBABN command is that it makes your next IPL abnormal. So if you are testing the system value QABNORMSW in your IPL start-up program, it will be set to '1' at the next IPL. That isn't a problem, it just lets you know that clean-up processing was done during the IPL.