Build an Expandable Disk Image¶
An expandable disk represents the system disk with the capability to auto expand the disk and its filesystem to a custom disk geometry. This allows deploying the same disk image on target systems with different hardware setup.
The following example shows how to build and deploy such a disk image based on openSUSE Leap using a QEMU virtual machine as the target system:
Make sure you have checked out the example image descriptions, see Example Appliance Descriptions.
Build the image with KIWI NG:
$ sudo kiwi-ng --type oem system build \ --description kiwi-descriptions/suse/x86_64/suse-leap-15.1 \ --target-dir /tmp/myimage
Find the following result images below
The disk image with the suffix
.rawis an expandable virtual disk. It can expand itself to a custom disk geometry.
The installation image with the suffix
install.isois a hybrid installation system which contains the disk image and is capable to install this image on any target disk.
The basic idea behind an expandable disk image is to provide the virtual disk data for OEM vendors to support easy deployment of the system to physical storage media.
There are the following basic deployment strategies:
Manually deploy the disk image onto the target disk.
Boot the installation image and let KIWI NG’s installer deploy the disk image from CD/DVD or USB stick onto the target disk.
PXE boot the target system and let KIWI NG’s installer deploy the disk image from the network onto the target disk.
The manual deployment method can be tested using virtualization software such as QEMU, and an additional virtual target disk of a larger size. The following steps shows how to do it:
Create a target disk
$ qemu-img create target_disk 20g
Retaining the Disk Geometry
If the target disk geometry is less or equal to the geometry of the disk image itself, the disk expansion performed for a physical disk install during the boot workflow will be skipped and the original disk geometry stays untouched.
Dump disk image on target disk.
$ dd if=Leap-15.1_appliance.x86_64-1.15.1.raw of=target_disk conv=notrunc
Boot the target disk
$ qemu -hda target_disk -m 4096
At first boot of the target_disk the system is expanded to the configured storage layout. By default the system root partition and filesystem is resized to the maximum free space available.
The deployment from CD/DVD via the installation image can also be tested using virtualization software such as QEMU. The following steps shows how to do it:
Create a target disk
Follow the steps above to create a virtual target disk
Boot the installation image as CD/DVD with the target disk attached.
$ qemu -cdromLeap-15.1_appliance.x86_64-1.15.1.install.iso -hda target_disk -boot d -m 4096
USB Stick Deployment
Like any other ISO image built with KIWI NG, also the installation image is a hybrid image. Thus it can also be used on USB stick and serve as installation stick image like it is explained in Build an ISO Hybrid Live Image
The deployment from the network downloads the disk image from a PXE boot server. This requires a PXE network boot server to be setup as explained in Setting Up a Network Boot Server
If the PXE server is running the following steps shows how to test the deployment process over the network using a QEMU virtual machine as target system:
Make sure to create an installation PXE TAR archive along with your disk image by replacing the following setup in kiwi-descriptions/suse/x86_64/suse-leap-15.1/config.xml
<type image="oem" installiso="true"/>
<type image="oem" installpxe="true"/>
Rebuild the image, unpack the resulting
Leap-15.1_appliance.x86_64-1.15.1.install.tar.xzfile to a temporary directory and copy the initrd and kernel images to the PXE server:
Unpack installation tarball
mkdir /tmp/pxe && cd /tmp/pxe tar -xf Leap-15.1_appliance.x86_64-1.15.1.install.tar.xz
Copy kernel and initrd used for pxe boot
scp pxeboot.Leap-15.1_appliance.x86_64-1.15.1.initrd.xz PXE_SERVER_IP:/srv/tftpboot/boot/initrd scp pxeboot.Leap-15.1_appliance.x86_64-1.15.1.kernel PXE_SERVER_IP:/srv/tftpboot/boot/linux
Copy the disk image, MD5 file, system kernel, initrd and bootoptions to the PXE boot server:
Activation of the deployed system is done via
kexecof the kernel and initrd provided here.
Copy system image and MD5 checksum
scp Leap-15.1_appliance.x86_64-1.15.1.xz PXE_SERVER_IP:/srv/tftpboot/image/ scp Leap-15.1_appliance.x86_64-1.15.1.md5 PXE_SERVER_IP:/srv/tftpboot/image/
Copy kernel, initrd and bootoptions used for booting the system via kexec
scp Leap-15.1_appliance.x86_64-1.15.1.initrd PXE_SERVER_IP:/srv/tftpboot/image/ scp Leap-15.1_appliance.x86_64-1.15.1.kernel PXE_SERVER_IP:/srv/tftpboot/image/ scp Leap-15.1_appliance.x86_64-1.15.1.config.bootoptions PXE_SERVER_IP:/srv/tftpboot/image/
The config.bootoptions file is used together with kexec to boot the previously dumped image. The information in that file references the root of the dumped image and can also include any other type of boot options. The file provided with the KIWI NG built image is by default connected to the image present in the PXE TAR archive. If other images got deployed the contents of this file must be adapted to match the correct root reference.
Add/Update the kernel command line parameters
Edit your PXE configuration (for example
pxelinux.cfg/default) on the PXE server and add these parameters to the append line, typically looking like this:
append initrd=boot/initrd rd.kiwi.install.pxe rd.kiwi.install.image=tftp://192.168.100.16/image/Leap-15.1_appliance.x86_64-1.15.1.xz
The location of the image is specified as a source URI which can point to any location supported by the
curlcommand. KIWI NG calls
curlto fetch the data from this URI. This also means your image, MD5 file, system kernel and initrd could be fetched from any server and doesn’t have to be stored on the
By default KIWI NG does not use specific
curloptions or flags. However it is possible to add custom ones by adding the
rd.kiwi.install.pxe.curl_optionsflag into the kernel command line.
curloptions are passed as comma separated values. Consider the following example:
The above tells KIWI NG to call
curl --retry 3 --retry-delay 3 --speed-limit 2048 -f <url>
This is specially handy when the deployment infraestructure requires some fine tuned download behavior. For example, setting retries to be more robust over flaky network connections.
KIWI NG just replaces commas with spaces and appends it to the
curlcall. This is relevant since command line options including commas will always fail.
The initrd and Linux Kernel for pxe boot are always loaded via tftp from the
Create a target disk
Follow the steps above to create a virtual target disk
Connect the client to the network and boot QEMU with the target disk attached to the virtual machine.
$ qemu -boot n -hda target_disk -m 4096
QEMU bridged networking
In order to let qemu connect to the network we recommend to setup a network bridge on the host system and let qemu connect to it via a custom /etc/qemu-ifup. For details see https://en.wikibooks.org/wiki/QEMU/Networking
The deployment process of an oem image can be customized through
oemconfig element which is a child section of the
element like the following example shows:
<oemconfig> <oem-swapsize>512</oem-swapsize> </oemconfig>
The following list of optional
oem element settings exists:
- oemconfig.oem-resize Element
Specify if the disk has the capability to expand itself to a new disk geometry or not. By default, this feature is activated. The implementation of the resize capability is done in a dracut module packaged as
oem-resizeis set to false, the installation of the corresponding dracut package can be skipped as well.
- oemconfig.oem-boot-title Element
By default, the string OEM will be used as the boot manager menu entry when KIWI creates the GRUB configuration during deployment. The
oem-boot-titleelement allows you to set a custom name for the grub menu entry. This value is represented by the
kiwi_oemtitlevariable in the initrd
- oemconfig.oem-bootwait Element
Specify if the system should wait for user interaction prior to continuing the boot process after the disk image has been dumped to the designated storage device (default value is false). This value is represented by the
kiwi_oembootwaitvariable in the initrd
- oemconfig.oem-reboot Element
Specify if the system is to be rebooted after the disk image has been deployed to the designated storage device (default value is false). This value is represented by the
kiwi_oemrebootvariable in the initrd
- oemconfig.oem-reboot-interactive Element
Specify if the system is to be rebooted after the disk image has been deployed to the designated storage device (default value is false). Prior to reboot a message is posted and must be acknowledged by the user in order for the system to reboot. This value is represented by the
kiwi_oemrebootinteractivevariable in the initrd
- oemconfig.oem-silent-boot Element
Specify if the system should boot in silent mode after the disk image has been deployed to the designated storage device (default value is false). This value is represented by the
kiwi_oemsilentbootvariable in the initrd
- oemconfig.oem-shutdown Element
Specify if the system is to be powered down after the disk image has been deployed to the designated storage device (default value is false). This value is represented by the
kiwi_oemshutdownvariable in the initrd
- oemconfig.oem-shutdown-interactive Element
Specify if the system is to be powered down after the disk image has been deployed to the designated storage device (default value is false). Prior to shutdown a message is posted and must be acknowledged by the user in order for the system to power off. This value is represented by the
kiwi_oemshutdowninteractivevariable in the initrd
- oemconfig.oem-swap Element
Specify if a swap partition should be created. By default no swap partition will be created. This value is represented by the
kiwi_oemswapvariable in the initrd
- oemconfig.oem-swapsize Element
Set the size of the swap partition. If a swap partition is to be created and the size of the swap partition is not specified with this optional element, KIWI will calculate the size of the swap partition and create a swap partition equal to two times the RAM installed on the system at initial boot time. This value is represented by the
kiwi_oemswapMBvariable in the initrd
- oemconfig.oem-systemsize Element
Set the size the operating system is allowed to consume on the target disk. The size limit does not include any consideration for swap space or a recovery partition. In a setup without a systemdisk element this value specifies the size of the root partition. In a setup including a systemdisk element this value specifies the size of the LVM partition which contains all specified volumes. Thus, the sum of all specified volume sizes plus the sum of the specified freespace for each volume must be smaller or equal to the size specified with the
oem-systemsizeelement. This value is represented by the variable
kiwi_oemrootMBin the initrd
- oemconfig.oem-unattended Element
The installation of the image to the target system occurs automatically without requiring user interaction. If multiple possible target devices are discovered the image is deployed to the first device.
kiwi_oemunattendedin the initrd