Hi, I'm running a QEMU instance on my Linode, and I have noticed that it freezes completely quite frequently. The QEMU virtual machine is running a minimal install of Debian Lenny, which is completely idle and has no services running besides those installed by default on Debian systems and an ssh daemon.

My Linode has 360 MB + swap, and I have assigned 248 MB to the QEMU virtual machine. The Linode itself isn't running anything except for default Debian services, the Zabbix agent and qemu.

I need to run a virtualized environment for testing purposes, but I'm worried about the frequent hangs. Is there a workaround for this or something I should check? If this is a known problem with QEMU running on top of a Linode, are there any virtualization alternatives that you could suggest?


Thanks in advance,
Alex

Disclaimer: this is personal opinion, and somebody will probably post to say that I'm wrong, but...

I find that it's generally not a good idea to double-virtualize (run an OS inside a virtual machine running on an OS inside a virtual machine running on an OS). Should it work? I've no idea, although I suspect not, since Linode isn't running Xen with VT (IE, you can't run Windows on your node).

Your Linode IS a virtualized environment.
If you need something for testing without disturbing your "production" Linode, then I recommend another Linode. I keep a spare linode for nothing more than testing updates, but if you only need to test things once in a while it is fairly cheap and easy to just create a new linode for a day or two.

Xen, by its nature, claims exclusive use of the VT-X technology on-chip. It's therefore not available to Linodes. Your performance will suffer drastically if you try this for any length of time.

As other posters have suggested, what is your need for an airtight virtualized environment?

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Disclaimer: I am no longer employed by Linode; opinions are my own alone.

Ok, I'd like to thank all the people that have shared their feedback on this issue.

Let me try the same question from a different angle.

Suppose that you needed to perform some testing that involved running an OS that is not GNU/Linux (let's say FreeBSD to give an example).

Is that possible on a Linode? In case it is, what virtualization product would you use to achieve that goal?

Just to clarify a few points:

• I am aware that a Linode is a virtual environment.
• I am aware that running a virtual machine on top a virtual machine has many drawbacks (a significant performance penalty being one of them)
• I'm not interested in performance (I'd just like to be able to run a different OS from time to time)

Thanks again,
Alex

Have you tried other VM software? VirtualBox? VMWare?

I've tried VirtualBox but so far I've been unable to compile the kernel module (vboxdrv).

Is there any guide to get VirtualBox working on a Linode?

Why?

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http://www.rejecttheherd.net

FreeBSD can run "natively" on a Linode. Windows, on the other hand, would be more trouble.

VirtualBox runs the guest OS ring0 in the (normally unused) ring1 of the host OS (while user code runs in ring3). The Xen Dom0 installs the hypervisor to take charge of ring0. Unless Xen were patched to support access to ring1, VirtualBox under Xen won't work. An old VirtualBox ticket (203) is related to this and is "closed: wontfix".

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/ Peter

That was qemu on Xen--I wonder if xen on xen would have better performance?
-r

The Xen host does not expose VT-X to guests, so I would imagine it'd roughly be the same.

EDIT: My first answer was not technically correct.

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Disclaimer: I am no longer employed by Linode; opinions are my own alone.

Hello! Is there any update on the matter? I've been trying to setup a Windows VM inside my linode with no success. Qemu doesn't work (bsod) and virtualbox won't compile the required modules. I need to serve a "legacy" silverlight applcation that is not critical for me, so i would like to avoid having to maintain a whole VPS just for that.

Linode is really not the best place for you if you need to run legacy Windows software. That said, you might look into Mono, the Linux implementation of .NET. I'd imagine you don't need to run Silverlight itself (since that's client-side), but you may need to run the .NET backend stuff?