How to stop Datacom Multi-User Facility (MUF) from being started twice.

Products

• Datacom
• DATACOM - AD

Issue/Introduction

Is there a mechanism within Datacom/AD and Datacom/DB that will stop starting the Multi-User Facility (called MUF) more than once?

Resolution

There are a number of protection and data integrity features built into Datacom. One of these items involves the use of the SIMPLIFY feature, which provides for a protective enqueue on the CXX, and which means that each CXX and MUF needs to have a unique name. 

A unique CXX name is not only a best practice but a requirement for using the SIMPLIFY feature in  Datacom/AD. To simplify naming standards, give the Datacom/AD MUF name and the CXX name the same value. Datacom forces an enqueue action on the CXX SYSPLEX wide for Datacom/AD. A good practice is a unique name for all CXX names for your site. Starting with Datacom/AD Version 14.0, the CXX name has no default value, therefore you must determine that unique value yourself.

While the above comments come from the Datacom/AD documentation, they apply equally to Datacom/DB using Simplify mode.

Once the first MUF is running, if you tried to start another one that was using the same CXX name, the second MUF would abend:

ABEND=S000 U0004 REASON=00000000 

and there would be two messages that identify this problem:

DB00242E - REQUIRED ENQ NOT AVAILABLE, MUFNAME=mufname
DB00205E - MULTI-USER ERROR - 0004  MUFNAME=mufname   SVC=000
 

From the Datacom/DB Message documentation:

DB00242E
REQUIRED ENQ NOT AVAILABLE, MUFNAME=mufname

Reason:
This message only occurs in z/OS if the Multi-User Facility (MUF) terminates with a user 4. The message occurs because another job, or another started task, owns the MUF control ENQ that is required.

If this message is followed by a DB00205E - MULTI-USER ERROR - 004 message, this MUF may not enable because the ENQ indicates another MUF is currently executing with the same identity this MUF wants to assume.

Action:
Take action as appropriate in reaction to the message text you received.



DB00205E
MULTI-USER ... ERROR - nnnn .optional-text.
. . .
04
NOT VALID WHEN MUF UP

Reason:
A function was executed that requires the Multi-User Facility to be stopped.

Action:
Before executing the function again, either wait until the Multi-User Facility has been stopped or stop it yourself using the EOJ option of the DBUTLTY COMM function or the related console command: COMM EOJ.

Therefore, the DB00242E error followed by the DB00205E - MULTI-USER ERROR - 0004 error, means that the MUF is already running.