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Fix pygrub booting of debian squeeze

Debian Squeeze is now using grub2 as the default bootmanager. Because of this pygrub has some difficulties to boot the domU after installing it. Here are the things i found out, if you have more remarks, drop me a comment please.


Direct mount xvda devices (or multi-partition isos)

Sometimes you will get in the need to directly mount an xvda device which is often used, if you (for example) install a debian virtual system in xen. Then this block device consists out of several partitions, which can not directly be used. But of course you can access the data of it, without the need of booting the guest os (domU).
This is the same if you get an iso or any other type block devices which uses multiple partion slices.


Using independent clocks in xen domU (ntp)

Normally the xen domU´s are using the same clock as the dom0. But I had the problem, that there was a timeshift of 20 minutes on one of my hosts. I did not find out the reason for this, so I decided to simply setup ntp also on this.

To make this work you have to tell the kernel of the virtual machine to use its on clock. With this command you set the parameter online.

echo 1 > /proc/sys/xen/independent_wallclock

To make this also boot safe, you will have to add a sysctl code to your /etc/sysctl.conf

# Set independent wall clock time

After that you can already use your own clock. For example you can now setup openntp on it, which will not work otherwise.

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