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Changing files during migration [message #13669]

Fri, 01 June 2007 12:47

Jun OKAJIMA
Messages: 30
Registered: March 2006

Member

Hello.

If I change/modifi/delete opened files during migration,
what happens?

For example....

1. I run a mail daemon ( like qmail or sendmail) in a VE.
2. Freeze the VE and create a suspend image.
In this moment, the daemon opens /var/spool/mail/* files.
3. Delete(or modify) /var/spool/mail/* stuff.
Opened files are deleted(modified) during migration!!!.
4. Restore the suspend image.

What happens?
It resumes or not?
Maybe whole OS (host OS) hangs?
Just the daemon gets "File read error" or something after resumed?
Or you can not resume the suspend image anymore?

This is an interesting trial, but a bit fear to do it on the real server...

--- Okajima, Jun. Tokyo, Japan.

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Re: Changing files during migration [message #13671 is a reply to message #13669]

Fri, 01 June 2007 13:05

dev
Messages: 1693
Registered: September 2005
Location: Moscow

Senior Member

Jun OKAJIMA wrote:
>
>
> Hello.
>
> If I change/modifi/delete opened files during migration,
> what happens?
>
> For example....
>
> 1. I run a mail daemon ( like qmail or sendmail) in a VE.
> 2. Freeze the VE and create a suspend image.
> In this moment, the daemon opens /var/spool/mail/* files.

how can daemon open the file if it is frozen (and the whole VE as well)?

> 3. Delete(or modify) /var/spool/mail/* stuff.
> Opened files are deleted(modified) during migration!!!.
> 4. Restore the suspend image.
>
> What happens?
> It resumes or not?
> Maybe whole OS (host OS) hangs?
> Just the daemon gets "File read error" or something after resumed?
> Or you can not resume the suspend image anymore?
>
> This is an interesting trial, but a bit fear to do it on the real server...
>
> --- Okajima, Jun. Tokyo, Japan.
>
>
>

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Re: Changing files during migration [message #13672 is a reply to message #13671]

Fri, 01 June 2007 13:23

Jun OKAJIMA
Messages: 30
Registered: March 2006

Member

>>
>> If I change/modifi/delete opened files during migration,
>> what happens?
>>
>> For example....
>>
>> 1. I run a mail daemon ( like qmail or sendmail) in a VE.
>> 2. Freeze the VE and create a suspend image.
>> In this moment, the daemon opens /var/spool/mail/* files.
>
>how can daemon open the file if it is frozen (and the whole VE as well)?
>
>

Wait, wait. sorry, not opens, but opened.

[HostOS]# vzctl 101 start
[HostOS]# vzctl 101 enter
[VE101]# /etc/init.d/sendmail start
.... sendmail opens /var/spool/mail/* in this moment.
[VE101]# exit
[HostOS]# vzctl 101 save
[HostOS]# rm -rf /var/lib/vz/root/101/var/spool/mail
[HostOS]# vzctl 101 restore

---> Then, what happens?

--- Okajima, Jun. Tokyo, Japan.

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Re: Changing files during migration [message #13673 is a reply to message #13672]

Fri, 01 June 2007 13:32

dev
Messages: 1693
Registered: September 2005
Location: Moscow

Senior Member

Jun OKAJIMA wrote:
>>>If I change/modifi/delete opened files during migration,
>>>what happens?
>>>
>>>For example....
>>>
>>>1. I run a mail daemon ( like qmail or sendmail) in a VE.
>>>2. Freeze the VE and create a suspend image.
>>> In this moment, the daemon opens /var/spool/mail/* files.
>>
>>how can daemon open the file if it is frozen (and the whole VE as well)?
>>
>>
>
>
> Wait, wait. sorry, not opens, but opened.
>
> [HostOS]# vzctl 101 start
> [HostOS]# vzctl 101 enter
> [VE101]# /etc/init.d/sendmail start
> .... sendmail opens /var/spool/mail/* in this moment.
> [VE101]# exit
> [HostOS]# vzctl 101 save
> [HostOS]# rm -rf /var/lib/vz/root/101/var/spool/mail
> [HostOS]# vzctl 101 restore
>
> ---> Then, what happens?

restore should fail. Changing VE filesystem from VE0
is a hack actually. It is convinient for management in
some situations, but you should understand what you do.
In this case you modify the filesystem of VE which is
frozen and doesn't expect files modifications.

So restore fails.

Thanks,
Kirill

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