Commit fc3914e6 authored by Iustin Pop's avatar Iustin Pop
Browse files

Document the selection of instance kernels

A simple doc patch to document how to configure the kernels for the
Signed-off-by: default avatarIustin Pop <>
Reviewed-by: default avatarMichael Hanselmann <>
parent 7adf7814
......@@ -371,6 +371,64 @@ non-managed configuration that the instance had, the transition should
be seamless for the instance. For more than one disk, just pass another
disk parameter (e.g. ``--disk 1:adopt=...``).
Instance kernel selection
The kernel that instances uses to bootup can come either from the node,
or from instances themselves, depending on the setup.
With Xen PVM, there are three options.
First, you can use a kernel from the node, by setting the hypervisor
parameters as such:
- ``kernel_path`` to a valid file on the node (and appropriately
- ``kernel_args`` optionally set to a valid Linux setting (e.g. ``ro``)
- ``root_path`` to a valid setting (e.g. ``/dev/xvda1``)
- ``bootloader_path`` and ``bootloader_args`` to empty
Alternatively, you can delete the kernel management to instances, and
use either ``pvgrub`` or the deprecated ``pygrub``. For this, you must
install the kernels and initrds in the instance, and create a valid grub
v1 configuration file.
For ``pvgrub`` (new in version 2.4.2), you need to set:
- ``kernel_path`` to point to the ``pvgrub`` loader present on the node
(e.g. ``/usr/lib/xen/boot/pv-grub-x86_32.gz``)
- ``kernel_args`` to the path to the grub config file, relative to the
instance (e.g. ``(hd0,0)/grub/menu.lst``)
- ``root_path`` **must** be empty
- ``bootloader_path`` and ``bootloader_args`` to empty
While ``pygrub`` is deprecated, here is how you can configure it:
- ``bootloader_path`` to the pygrub binary (e.g. ``/usr/bin/pygrub``)
- the other settings are not important
More information can be found in the Xen wiki pages for `pvgrub
<>`_ and `pygrub
For KVM also the kernel can be loaded either way.
For loading the kernels from the node, you need to set:
- ``kernel_path`` to a valid value
- ``initrd_path`` optionally set if you use an initrd
- ``kernel_args`` optionally set to a valid value (e.g. ``ro``)
If you want instead to have the instance boot from its disk (and execute
its bootloader), simply set the ``kernel_path`` parameter to an empty
string, and all the others will be ignored.
Instance HA features
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