Automated disk partitioning on virtual machines with Cobbler

The default Cobbler Snippets just do simple auto partitioning. For a more sophisticated partition layout you need to know what kind of VM you are going to install. KVMs and RHEVs device name is /dev/vda, Xen uses /dev/xvda and ESX /dev/sda.

Luckily this can be figured out automatically, those different virtualization vendors are using its own MAC prefixes. So we can add two nice small Cobbler snippets to do the job. In this example, I call them hw-detect and partitioning.

hw-detect

#set $mac = $getVar('$mac_address_eth0')
#if $mac
#set $mac_prefix = $mac[0:8]
#if $mac_prefix == "00:1a:4a"
# This is a RHEV virtual machine
#set global $machinetype = 'kvm'

#else if $mac_prefix == "52:54:00"
# This is a KVM/Qemu virtual machine
#set global $machinetype='kvm'

#else if $mac_prefix == "00:16:3e"
# This is a XEN virtual machine
#set global $machinetype='xen'
#
#else if $mac_prefix == "00:50:56"
# This is a ESX virtual machine
#set global $machinetype = 'esx'

#else
# #This is a physical machine
#set global $machinetype = 'physical'
#end if
#end if

partitioning

#if $machinetype == 'kvm'
#set $disk='vda'
#else if $machinetype == 'xen'
#set $disk = 'xvda'
#else
#set $disk = 'sda'
#end if
# Lets install the system on /dev/$disk
part /boot      --fstype ext2 --size=250 --ondisk=$disk
part pv.0       --size=1 --grow --ondisk=$disk

volgroup vg_${name} pv.0

logvol /        --fstype ext4 --name=lv_root    --vgname=vg_${name} --size=4096
logvol /home    --fstype ext4 --name=lv_home    --vgname=vg_${name} --size=512 --fsoption=nosuid,nodev,noexec
logvol /tmp     --fstype ext4 --name=lv_tmp    --vgname=vg_${name} --size=1024 --fsoption=nosuid,nodev,noexec
logvol /var     --fstype ext4 --name=lv_var    --vgname=vg_${name} --size=2048 --fsoption=nosuid,nodev,noexec
logvol swap     --fstype swap --name=lv_swap    --vgname=vg_${name} --size=2048

An additional “feature” of the partitioning Snippet is: It sets up the Volume Group name according to your systems name. This is the unofficial standard since quite some time. It also sets some more secure mount options. Review them carefully if they make sense for you and edit them as needed.

The next step is to configure your kickstart template.

Standalone Cobbler
On a standalone Cobbler server edit /var/lib/cobbler/kickstart/your-kick-start-template.ks

# Detect the used hardware type
$SNIPPET('hw-detect')
# Set up default partitioning
$SNIPPET('partitioning')

Bundled Cobbler
When using cobbler bundled with Spacewalk or Red Hat Satellite, you need to edit the Kickstart profile in the WebUI.


Navigate to Systems -> Kickstart -> Profile. Select the Kickstart profile to be modified -> System Details -> Partitioning.

Copy the two Snippets in /var/lib/cobbler/spacewalk/1, where 1 is representing your OrgId.

Alternatively you can edit them in the WebUI as well.

To check if all is working as expected, add a system to Cobbler using the Command Line Interface and have a look to the rendered Kickstart file. This can be easily done with cobbler system getks --name=blah.

Happy System installing….

Have fun :-)

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    2 Responses to “Automated disk partitioning on virtual machines with Cobbler”

    1. Rich says:

      I’m pretty sure this won’t work in the general case of a KVM guest that has emulated (eg. IDE or SCSI) disks, since that would use /dev/sda. Nor for a KVM guest that uses modern virtio-scsi (/dev/sda too). Nor a KVM guest that has an arbitrary MAC address.

      Why not just probe /dev/sda, /dev/vda and /dev/xvda in turn until you find one which exists?

      • Luc de Louw says:

        Well, nobody that installs a Fedora or RHEL breed distro uses IDE or SCSI emulation. Arbitrary MAC address are generally not the best idea, as it can cause conflicts (I know, there are some use cases when using closed source software with the license bound to the MAC).

        This procedure works fine with Fedora 13+ and EL 5.4+

        The reason why I try to realize as much as possible with Cobbler snippets is its simplicity.