[GE users] problem with migrating to shadow master

rumpelkeks tina.friedrich at diamond.ac.uk
Tue Nov 23 09:34:49 GMT 2010


Hi Reuti,

>> Hello list,
>>
>> I have just discovered that I can't seem to migrate my qmaster service
>> any more (it definitely used to work).
>>
>> I get the "old qmaster did not write lock file. Cannot migrate qmaster."
>> error. If I manually touch a file called 'lock' in the spool directory,
>> all works fine. Oh plus it successfully shuts down the qmaster (just
>> never starts one). So I've probably traced it down to 'no lock file'.
>>
>> Have found nothing in the logs to explain it either.
>>
>> Now. Need some pointers for further debugging.
>>
>> I don't quite understand this 'locking' mechanism - when and where (and
>> where to) is the 'lock' written? (I can't really find anything in the
>> startup script that writes the file, only things that check for it). Is
>> this something that the old qmaster writes when it's shutting down and
>> the new one only starts once it appears? (There certainly is no 'lock'
>> file in the spool directory when the qmaster is running.)
>
> AFAIK: the lock file is written by the qmaster, and removed when it's shut down in a proper fashion. But when it crashes, the file will stay there and the heartbeat file won't be updated any longer. Then the shadow master decides to take over and start a now qmaster.
>
> Do you have a file $SGE_ROOT/default/common/shadow_masters?
>
> -- Reuti

I do have a shadow_masters file, yes.

Failover in case one dies appears to work (i.e. if I kill the qmaster 
process, eventually the shadow master starts it). It's the manual 
migrate (by calling the startup script with -migrate) that's not working 
at the moment.

I do not appear to have any lock file 'in residence' though. I've 
discovered (further testing) that it appears to work when migrating from 
'master B' to 'master A', but not 'master A' to 'master B'. With the 
successsful migration, a file $SGE_ROOT/$SGE_CELL/spool/qmaster/lock 
makes a brief appearance. It is, however, not there in normal operation 
- looks to me as if the shutting down master creates it only on 
shutdown, which puzzled me. (In case of the unsuccessful migration 
attempt, there never is a $SGE_ROOT/$SGE_CELL/spool/qmaster/lock file. 
Also if I manually touch one, migration works.)

Tina

-- 
Tina Friedrich, Computer Systems Administrator, Diamond Light Source Ltd
Diamond House, Harwell Science and Innovation Campus - 01235 77 8442

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