Each new release of OS/400-i5/OS seems to bring a new set of system jobs -- those jobs on the WRKACTJOB screen that have a type SYS. These jobs are responsible for things such as keeping cross-reference information updated, maintaining access paths, handling system arbitration, and just about everything related to TCP/IP.
By default, all but a handful of these jobs run at a very high priority, between 0 and 20 (0 is the highest priority, 99 the lowest). For comparison, the default run priority for interactive jobs is 20, so these system jobs are running at the same or higher priority than normal interactive jobs.
In fact, most system jobs run at the ultimate priority of 0. Nothing gets in their way, and God forbid one of them to start looping. Don't laugh -- it happens. If you keep up with "The PTF Report" in each month's issue of Inside Version 5, you may recall seeing a number of PTFs that fix system looping problems. Well, guess what's looping?
How to use the CHGSYSJOB command
The Change System Job command (CHGSYSJOB) lets you "configure" system jobs. I use the term "configure" lightly because the only job attribute that the CHGSYSJOB command can change is the run priority. (But we'll take anything we can get, right?)
The CHGSYSJOB command has two parameters:
- Job name (JOB): Specify the name of the system job you want to change. To see a list of eligible jobs, press F4.
- Run priority (RUNPTY): Specify the new priority under which you want the job to run. You can specify any priority between 0 and 99, inclusive. You can also specify the special value *IPL to reset the job's run priority back to the default setting (i.e., the run priority that it was assigned at the last IPL).
The catch . . .
Before running off thinking you're going to super-tune all the system jobs, you may want to keep this little ditty in mind: Only a few system jobs can be changed with the CHGSYSJOB command. Most system jobs are not eligible, and if you try to specify them, you will get an error. To determine which system jobs can be changed with the CHGSYSJOB command, prompt the command with F4 and then prompt the Job name parameter (again with F4 as described above). You will then see a list of system jobs on your system that can be changed with the CHGSYSJOB command.
The system jobs that cannot be changed are so vital to proper system operation that changing their run priority may compromise the integrity of the system. So, to prevent an accidental -- or otherwise -- crash of the system, you cannot change the run priority of these jobs.
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About the author: Ron Turull is editor of Inside Version 5. He has more than 20 years' experience programming for and managing AS/400-iSeries systems.
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