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I have a virtualization server which is having a few virtual machines running at top of it. All this was done using Ubuntu server edition with KVM and using virt-manager on SSH connection.

These VMs are Lucid 10.04 64 bit Vms. When I upgrade them via
apt-get upgrade on an SSH connection in between the ncurses screen, it asks me if it should install a bootloader and to select Yes or No for it.

I have no clue what should I select here and I cancel the upgrade.Since it is a production machine I can not specify any thing like this. So let me know what will be a correct.

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2 Answers 2

This depends on how the machine boots. You'll need a boot loader if your machine is not set up for 'direct kernel boot'

You can check this by opening virt-manager, looking at the properties for the virtual machine, and selecting the 'boot options' configuration panel. If the 'Kernel path' setting is set (it's under the 'Direct kernel boot' drop-down), then the OS will be loaded by KVM, and you don't need a bootloader.

If this is empty, then you will need a bootloader to load the kernel from the virtual disk.

You can also check this parameter with virsh:

virsh dumpxml <virtual-machine>

this will dump the KVM configuration data for the machine. Look for the <os> tag. If it has a <kernel> tag, like this:

    <os>
     <type arch='x86_64' machine='pc-0.11'>hvm</type>
     <kernel>/var/lib/libvirt/images/vmlinuz-2.6.32-29-server</kernel>
     <initrd>/var/lib/libvirt/images/initrd.img-2.6.32-29-server</initrd>
     <cmdline>root=/dev/vda console=ttyS0 ro debug nosplash</cmdline>
     <boot dev='hd'/>
    </os>

Then the kernel will be loaded with KVM, and no bootloader is required. If there is no <kernel> tag, you need a bootloader.

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KVM hosts full installation of other OS, thus you have to have "the usual stuff" you have on system, and that includes bootloader, that will boot when KVM starts to run image/partition when your KVM tries to start that VM.

In your case, I would test exactly how everything happens as no amount of reading will fix your production server instantly if you manage to corrupt something.

Making backup of working VM files is also a good idea.

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I understand your point I work in an educational environment where we do not have any other server (that supports VT) so I wish I could do the experiment you said. –  Bond Jan 28 '11 at 14:09

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