New (undocumented?) system parameters

[VMS Support]

Whilst setting up a new V7.3-2 system I have come across three new system parameters that I can't find in the documentation, help, release notes or searches on the HP web site & Google.

Can anyone explain MPW_STACKPAGES, DEFUID & DEFGID, please?

[Richard Whalen]

The help on an F8.3 system doesn't have anything about them, but here are some guesses:

MPW is the Modified Page Writer, so I would guess that MPW_STACKPAGES is the stack size allocated to the MPW code. The MPW probably needs its own special stack in order to work correctly.

My guess for DEFUID and DEFGID are that they are NFS related.

[Ian Miller.]

MPW_STACKPAGES MPW Stack Pages
MPW I would guess is the modified page writer.


DEFUID default POSIX UID

DEFGID default POSIX GID

[Ian Miller.]

More research on MPQ_STACKPAGES found a comment in the listings for mpw$gl_stackpages

- Modified Page Writer STACK SIZE - ESTABLISHES THE SIZE OF THE STACK in the KPB of the MPW.

A KPB is a kernel process block. I guess the SWAPPER proces must be using the KP services.

Searching the V7.3-2 listings I found no use of the mpw$gl_stackpages.

[John Gillings · Accepted solution]

OpenVMS engineering may take several versions to completely implement a new feature or improvement in behaviour. That can lead to "latent support" being introduced earlier than the actual feature.

Sometimes there are undocumented SYSGEN parameters, run time library routines or even entire images.

They're required as infrastructure for engineering to develop and test new code scheduled for a later release. Sometimes the proposed feature or switch is never released (for example, see the UAF fields SHRFILLM and PBYTLM - they've been around from V1.0, but never actually did anything!)

We can all have fun guessing what they might be intended for, but I'd suggest you concentrate on all the other the SYSGEN parameters.

Be assured that when/if these apparently new parameters become important, they will be documented. In the mean time, it's best to just leave them alone. It's also possible they may quietly vanish in a future release.

Remember undocumented means unsupported.

[Ian Miller.]

John, all true. DEFUID and DEFGID do appear to do something. MPW_STACKPAGES does not.

[VMS Support]

Thank you all - I'll leave at default values!