[Gllug] Xen - bit of a ramble

[- Tethys]

On 5/15/06, Adrian McMenamin <adrian at mcmen.demon.co.uk> wrote:

> I had forgotten, of course, that Fedora installs SE Linux by default so
> when I realised that appeared to be messing up by system I removed the
> SELinux rpms

That's a bit of a drastic way of going about it. A simple "setenforce
0" would have sufficed...

> But when I finally get that done, and get guest systems installed etc, how
> do I access the virtual systems over ssh or similar? There isn't much
> about this to be found anywhere.

No, the one area where Xen really falls down is documentation. Quite
frankly, there isn't anywhere near enough of it. Most of what I needed
to know, I found by trawling mailing list archives.

You can access the virtual OSes either by sshing into them (which
would be the normal way of going about it), or by getting a console on
them. Xen will provide you with effectively a serial console to the
machine:

xm console machine_name

What it doesn't document is how to get out of that (you use ^], the
same as for telnet).

> http://ftp.hpl.hp.com/techreports/2004/HPL-2004-207R1.pdf suggests using
> vnc but what about simple cli access? And how does networking work - can I
> assume that the whole xen system is a bit like a NAT-in-a-box?

Xen networking sucks. It works OK, but it's hideously complex. There's
a page about it on their wiki:

http://wiki.xensource.com/xenwiki/XenNetworking

You basically have the choice of going with a bridged network, or just
routing (and potentially NATing) via the dom0 box. Pay attention to
your iptables rules, though. All of the virtual machines packets go
via the FORWARD chain -- but so do those from dom0 to the outside
world, unintuitive as that may be...

Tet
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