6/30/09 There's a backup version of the controlling subsystem (QCTL)

If you’ve changed attributes of the QCTL subsystem and lost track of what the defaults should be, or worse yet you’ve changed the controlling subsystem in some way that the system refuses to IPL properly, there’s a little known “backup” version of the controlling subsystem called QSYSSBSD. It’s specially protected so that it cannot be changed, only displayed. It’s always there, in the QSYS library, waiting for you “just in case”.

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herbina said...

after knowing QSYSSBSD,how doyuo see its contents???

Stefan said...
This comment has been removed by the author.
Stefan said...

the old comment had
some nasty spelling :)

You can use the DSPSBSD command to view it. WRKSBSD will also work.

Although you can use CHGSBSD, when you complete the command, it will give you an error telling you the subsystem "can not be changed"

Jim said...

I think the tip meant to say that the backup subsystem QSYSSBSD is in the QSYS library. I'm not aware of a QCTL library supplied by IBM at any release. You may want to correct the tip.

Stefan said...
This comment has been removed by a blog administrator.
Vision Solutions said...

Thanks for noticing, Jim. This is fixed.

Muktar said...


How to use the subsystem? If we start the sub-system, will it provide me the session or I need to create the session under the sub-system?


Vision Solutions said...

If your question is correctly understood, you are referring to workstation entries. Because the subsystem can not be changed, you have to make do with the default entry of *CONS. This means, you have to use the system console to sign-in.

In most cases, the backup subsystem is used because the system IPL fails with a B900-3C20 or similar SRC code resulting from a change to the controlling subsystem description (QCTL) that makes it unusable.

During a manual IPL, select the option to "define or configure the system during IPL". That will give you access to change the system value QCTLSBSD, and specify the backup subsystem QSYSSBSD in library QSYS. You would also then select the option to "start this device only", and bring the system up into a restricted state. You can then fix the real controlling subsystem, change the QCTLSBSD system value back to what it was originally (in most cases, QCTL or QBASE), and then re-IPL.