[one-users] Non clonable readonly shared OS image?

[Ismael Farfán]

2011/9/8 Fabian Wenk:
> Hello Ismael
>
> Usually every Unix like OS does write to the disk, mostly in /var/ eg. log,
> pid and lock files. Now when you have several VMs writing to the same disk
> based file system during the same time, it will corrupt the file system.
> There is no clean file locking available when a file system on a disk (or
> image) is mounted from more then one running OS.

I thought that those pseudo FS lived in the RAM... but now that explains
why fsck threw so many errors.

> I guess your only chance is to create a Live CD based on your own
> installation (your distribution should provide tools to do this), then it
> should work, as an OS bootet from Live CD does create union mounts with a
> RAM disk, so writing to the file system is going into RAM and not written
> back to the disk (in this case the ISO image).

OK, I'll try to turn my VM into a live CD.

>> Mainly I was wondering why with readonly=yes the VM doesn't boot at
>> all, it fails before even calling kvm and I can't figure out why.
>
> I guess this is not supported from ONE if an OS image (not CD image) is set
> to read only, and it will abort at an early stage. Did you see anything in
> the log/one/<VID>.log file?

I attached the log (almost the same as in the firs mail), whatever ONE does
different while setting the image as readonly makes libvirt trow this error that
I haven't been able to fix jet:
failed to retrieve chardev info in qemu with 'info chardev'

>> I'll try modifying fstab to mount / as readonly and set readonly=no in the
>> VM description file, maybe that'll work.
>
> I guess your OS will then not work properly and have some other strange
> problems, if the / is read only.

Yeah, at least all the contextualization work just fails.

>> 2011/9/7 Matthew Smith:
>>>
>>>  Hi
>>>
>>>  Have you tried doing this with a 'live CD' distribution image (which is
>>> by
>>>  its nature normally a read only boot)?
>>
>> I haven't. The idea is that my OS image works as a live CD since I need to
>> install some random stuff until it works as a virtual cluster.
>
> During the first phase (as long as you need to setup your system), just
> create a persistent disk image and run a single VM with it. When you have
> everything installed as needed, use the tools from your distribution to
> create a Live CD. Eventually you need to start your installation based on
> the Live CD provided from your distribution. When you have created your Live
> CD you have to register this ISO image in ONE. And then you can create
> several VMs which use the registered ISO image (as CD) as the boot file
> system.

Thanks, I'll try that.
Ismael

> bye
> Fabian
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>



-- 
[============================]
How do you create an operating system on Linux Ubuntu 9.10?
Y luego que por qué no me gusta usar Ubuntu...
[============================]
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