Hi,
The following email is only relevant to people who have upgraded, or
who are thinking of upgrading their VPS to Debian lenny, Debian sid,
a very new unsupported by bitfolk distribution, or a new kernel from
kernel.org. If that doesn't sound like you then you can most likely
skip this email.
As you may be aware, the Xen code that bitfolk VPSes are based on is
developed externally from the Linux upstream kernel. The problem
with this is that the authors of Xen concern themselves only with
Xen functionality and their kernel languishes at version 2.6.18,
meanwhile the upstream kernel moves on to support new hardware and
include bug and security fixes. It's currently at 2.6.26.2.
Distributors of the Linux kernel, such as Debian, Ubuntu, Centos,
Gentoo etc. are forced to port the Xen patch into their up-to-date
kernels, which is a lot of work.
Dissatisfaction with this state of affairs led to an effort to
include more of the Xen functionality in the upstream kernel, but
in a more generic way that could apply to the multiple competing
virtualisation technologies that Linux can take advantage of. This
support is called "pvops" or "paravirtual operations."
"pvops" support in the Linux kernel is now sufficient to run a Xen
domU (i.e. a VPS kernel) and as a result some of the newer Linux
distributions are shipping kernels using this technology rather than
code directly from the authors of Xen. A notable example is Debian
Lenny, whose packaged Xen kernel is actually an upstream kernel with
pvops support turned on. It's the same story with newer Centos and
of course with a vanilla upstream kernel you might download today.
There are some configuration differences required to use one of
these kernels though, and if you upgrade your distribution to use
a pvops kernel you may get bitten by this. Here is some more
information:
http://wiki.xensource.com/xenwiki/XenParavirtOps
Notably the "Running" part.
Also note that at the time of writing, pvops kernels do not support
save/restore.
The basic things you need to do when preparing to run a pvops kernel
are:
- make sure to put:
console=hvc0
on your kernel boot line, otherwise your VPS will boot without a
console (the thing you get to via xen-shell when you type
"console")
- make sure to put something like:
co:2345:respawn:/sbin/getty 38400 hvc0
(or like whatever else your distribution uses there for tty1) in
/etc/inittab otherwise you will have a console that the kernel
outputs to, but it will not have a login prompt on it.
- make sure that:
/dev/hvc0
is in /etc/securetty, otherwise you'll have a login prompt but the
system will not allow root to log in there.
Alternatively you could continue using the Debian etch Xen kernels,
which are based on 2.6.18 with security backports, until etch is no
longer supported.
Personally most of my virtual machines are based on Debian etch so I
will be doing that, but I have tested Debian lenny's Xen kernel in
this way and it seems fine. Anyone who asks for Debian lenny or
Debian sid VPSes is getting the packaged Xen kernel, which is pvops.
Cheers,
Andy
--
http://bitfolk.com/ -- No-nonsense VPS hosting
Encrypted mail welcome - keyid 0x604DE5DB
