As mentioned in http://blog.defunct.ca/?p=411, I’m running OpenStack on a XenServer virtual machine and need to be able to use something like UML to run instances from within the VM. I had to hack a number of things in order to get this to work.
First things first. Let’s get install user-mode-linux:
# apt-get update # apt-get install user-mode-linux
Now, grab the CentOS 5.6 x86_64 image from http://fs.devloop.org.uk/ (we’re using a 64-bit XenServer VM):
# cd /root # wget http://fs.devloop.org.uk/filesystems/CentOS-5.6/CentOS5.6-AMD64-root_fs.bz2 # bunzip2 CentOS5.6-AMD64-root_fs.bz2
There is an image on http://wiki.openstack.org/Nova/UML, however I couldn’t get this image to boot properly. As such, I opted for the CentOS 5.6 image above.
A few things within the image needed adjusting, so I:
# mkdir /mnt/image # losetup --find --show CentOS5.6-AMD64-root_fs /dev/loop0 # mount /dev/loop0 /mnt/image # cp -a /usr/lib/uml/modules/2.6.35.1/ /mnt/image/lib/modules/ # chroot /mnt/image # sed -i 's@LABEL=ROOT@/dev/ubda@g' /etc/fstab # chkconfig network on # exit # umount /mnt/image # losetup -d /dev/loop0
Note that /usr/lib/uml/modules/2.6.35.1/ is provided by the user-mode-linux package on Ubuntu 10.10, so adjust accordingly to what you’re running. Also, UML seems to use device /dev/ubda, so we modify /etc/fstab w/ that.
Now we can bundle up the image:
# cd /root # euca-bundle-image -i CentOS5.6-AMD64-root_fs # euca-upload-bundle -b uml-image-bucket -m /tmp/CentOS5.6-AMD64-root_fs.manifest.xml # euca-register uml-image-bucket/CentOS5.6-AMD64-root_fs.manifest.xml
Once that’s done, we remove this from /etc/nova/nova.conf:
--libvirt_type=qemu
… and add this:
--libvirt_type=uml --use_cow_images=false --libvirt_xml_template=/etc/nova/libvirt.xml.template
Since I’ve specified –libvirt_xml_template in /etc/nova/nova.conf, we need to now create that file:
# cp -a /usr/share/pyshared/nova/virt/libvirt.xml.template /etc/nova/libvirt.xml.template
Now open up /etc/nova/libvirt.xml.template and remove the following:
#if $getVar('vncserver_host', False)
<graphics type='vnc' port='-1' autoport='yes' keymap='en-us' listen='${vncserver_host}'/>
#end ifThe reason for doing this is because it appears that we run into an issue similar to the one reported in here. Update: I’ve since created a bug report for this UML issue here.
Now we can restart the nova-compute service and create an instance:
# service nova-compute restart # euca-run-instances ami-778c501e -k mykey -t m1.tiny
(replace ami-778c501e with your image name, which can be found by running euca-describe-images)
If your instance doesn’t go into a running state, have a look at the libvirt.xml file under /var/lib/nova/instances/####/ (replacing #### w/ your instance’s name, found by running euca-describe-instances), ensuring that there is no reference to the vnc stuff in there. If there is, then the template hasn’t been updated or isn’t being used correctly. Otherwise, your instance should be ssh-able, using the IP returned by euca-describe-instances.