XEN on LCFG

The following resources will turn a normal LCFG Linux box into an LCFG Linux XEN host.

At first place, the right packages should be installed and therefore the XEN package list must specified in the machines profile:

#include <lcfg/options/xen.h>

One package that is not included in this list, is the RPM of the lcfg-xen component. This is available from at http://lcfg.ucs.ed.ac.uk/pkgs/devolved/world/sl5/rpms/lcfg-xen-0.99.3-1.noarch.rpm It will need to be added in the profile as well:

!profile.packages mADD(lcfg-xen-0.99.3-1/noarch)

Next step is to populate existing resources with the lcfg-xen component. The following lines add the component in the component list of the machine, enable logserver to provide web based information, and is configured to start and stop automatically at boot and shutdown respectively:

!profile.components      mADD(xen)
profile.version_xen      1
!logserver.components    mADD(xen)

!boot.services           mADD(lcfg_xen)

!boot.stop_lcfg_xen  5 restart

Because the previously defined lcfg/options/xen.h will install the XEN kernel, we'll need to create the appropriate symlinks for the kernel, initrd and the gz image. Otherwise, having a new XEN kernel installed after an update, the system will not be able to find the old kernel and will be unable to boot. The following resource will do the trick:

!kernel.kerneltype mSET(xen)

Having that done, what's left is configuring Grub in order to boot the XEN kernel:

!grub.menuitems_defaultboot mADD(xen)
grub.root_defaultboot_xen (hd0,4)
grub.kernel_defaultboot_xen /boot/xen.gz
grub.modules_defaultboot_xen kernel initrd
grub.module_defaultboot_xen_kernel /boot/vmlinuz root=/dev/sda5 ro quiet selinux=0
grub.module_defaultboot_xen_initrd /boot/initrd.img
grub.boot_defaultboot_xen yes
grub.title_defaultboot_xen Scientific Linux (XEN)
!grub.defaultboot_defaultboot mSET(4)

Depending on which drive/partition your LCFG installation lives, you may need to change the grub.root_defaultboot_xen (hd0,4) and grub.module_defaultboot_xen_kernel /boot/vmlinuz root=/dev/sda5 ro quiet selinux=0 resources. The last line, !grub.defaultboot_defaultboot mSET(4), sets the XEN entry to be the default for booting. The number 4 in the parenthesis states that the fifth Grub entry should become the default for booting. In order to get the right numbering, you have to count your entries from top to bottom starting from 0.

Resources example:

            !xen.virtualmachines           mADD(sl5vm)
            !xen.name_sl5vm                mSET(sl5vm)
            !xen.uuid_sl5vm                mSET(6f2cffa1-21f6-43b4-8c52-08b8277a38a3)
            !xen.maxmem_sl5vm              mSET(1024)
            !xen.memory_sl5vm              mSET(1024)
            !xen.vcpus_sl5vm               mSET(2)
            !xen.disks_sl5vm               mADD(osdisk, swap)
            !xen.diskname_sl5vm_osdisk     mSET(sl5vmos)
            !xen.disktype_sl5vm_osdisk     mSET(image)
            !xen.disksize_sl5vm_osdisk     mSET(24)
            !xen.diskname_sl5vm_swap       mSET(sl5vmswap)
            !xen.disktype_sl5vm_swap       mSET(image)
            !xen.disksize_sl5vm_swap       mSET(1)
            !xen.diskpath_sl5vm_swap       mSET(/var/lib/xen/images/swap)
            !xen.vifs                      mADD(vif1 vif2)
            !xen.mac_vif1                  mSET(00:1e:c9:52:30:ce)
            !xen.mac_vif2                  mSET(00:1e:c9:51:32:ac)
            !xen.bridge_vif2               mSET(xenbr1)
            !xen.script_vif2               mSET(network-bridge-private)
            !xen.boot_sl5vm                mSET(yes)

Based on these resources the component will create a new guest called sl5vm and its configuration file will be /etc/xen/sl5vm. A specific UUID is given, 1G of memory will be allocated and two CPUs will be used. The component will create two disk images. 24G for the system disk and 1G for a disk image to be used as swap memory. The swap disk image will be stores in a different location than the default, /var/lib/xen/images/swap. The guest will also have two network interfaces (eth0 and eth1). The second one will be assigned a private LAN address.

Doing a 'man lcfg-xen' will give you a description of all the available resource followed by syntax.

NOTE: The current version of the component (0.99.3-1) assumes that the top level directory where the disk image will be stored already exists. That is not the case every time. Apply the following patch to /usr/lib/lcfg/components/xen for getting the directories created in case they don't exist. The patch will also make the component to check if the directory and the disk image have been created successfully. These operations will be added on the next release of the component.

Patch: http://www2.epcc.ed.ac.uk/~pkritika/lcfg/lcfg-xen-0.99.3-1.1a.patch

To apply the patch run: # patch /usr/lib/lcfg/components/xen lcfg-xen-0.99.3-1.1a.patch

XEN guest

If you got your LCFG machine running as XEN host, then you can also get XEN guests running within the host. There is no automatic way of creating the guest, the building process is the same as for a normal LCFG machine (you'll need of course go through steps that of creating the initial XEN virtual machine configuration). The profile of the guest should have the following hardware resources:

!inv.model              mSET(XEN Virtual Machine)

/* Adding IDE support */

!fstab.disks                    mSET(hda)
!fstab.partitions_hda           mSET()
!fstab.dopartition_hda          mSET(no)
!fstab.spec_root                mSUBST(sda,hda)
!fstab.spec_swap                mSUBST(sda,hda)
!fstab.spec_pie                 mSUBST(sda,hda)

!grub.installdev                         mSUBST(sda,hda)
!grub.kroot_defaultboot_disk1            mSUBST(sda,hda)
!grub.kroot_defaultboot_disk1single      mSUBST(sda,hda)
!grub.timeout_defaultboot mSET(0)

/* end of IDE support */

/* Add modules */

!hardware.modlist       mADD(eth scsi)

hardware.mod_eth        alias eth0 tg3
hardware.mod_scsi       alias scsi_hostadapter ata_piix

The IDE support configuration may need to be changed according to your local setup.

-- Main.pkritika - 04 Sep 2008