Booting a Live ISO Image from Network

In KIWI NG, live ISO images can be configured to boot via the PXE boot protocol. This functionality requires a network boot server setup on the system. Details how to setup such a server can be found in Setting Up a Network Boot Server.

After the live ISO was built as shown in Build an ISO Hybrid Live Image, the following configuration steps are required to boot from the network:

  1. Extract initrd/kernel From Live ISO

    The PXE boot process loads the configured kernel and initrd from the PXE server. For this reason, those two files must be extracted from the live ISO image and copied to the PXE server as follows:

    $ mount kiwi-test-image-live.x86_64-1.15.6.iso /mnt
$ cp /mnt/boot/x86_64/loader/initrd /srv/tftpboot/boot/initrd
$ cp /mnt/boot/x86_64/loader/linux /srv/tftpboot/boot/linux
$ umount /mnt

    Note

    This step must be repeated with any new build of the live ISO image

  2. Export Live ISO To The Network

    Access to the live ISO file must be provided by either ftp, http, https or dolly. The most simple method is to setup a FTP server e.g. vsftpd and copy the live ISO file to the data directory:

    $ mkdir -p /srv/ftp/image
$ cp kiwi-test-image-live.x86_64-1.15.6.iso /srv/ftp/image

    Note

    Check if the image can be downloaded via: wget ftp://IP/image/kiwi-test-image-live.x86_64-1.15.6.iso before the next step.

  3. Setup live ISO boot entry in PXE configuration

    Note

    The following step assumes that the pxelinux.0 loader has been configured on the boot server to boot up network clients

    Edit the file /srv/tftpboot/pxelinux.cfg/default and create a boot entry of the form:

    LABEL Live-Boot
    kernel boot/linux
    append initrd=boot/initrd ip=dhcp root=live:ftp://IP/image/kiwi-test-image-live.x86_64-1.15.6.iso

    • The ip= parameter controls how the dracut network module sets up the network. Several options exists to control how the network interface should be setup. Please consult the dracut manual for further information.

    • The boot parameter root=live:PROTOCOL://IP/PATH... specifies the remote endpoint and protocol to find the live ISO file. So far ftp, http, https and dolly are supported.

  4. Boot from the Network

    Within the network which has access to the PXE server and the IP in the root= option, any network client can now boot the live system. A test based on QEMU is done as follows:

    $ qemu -boot n

Available Remote Boot Options

There are the following kernel boot options available to control the behavior of the remote boot process.

rd.kiwi.live.curl_options=

Options passed along to the curl call

rd.kiwi.live.dolly_options=

Options passed along to the dolly call

rd.kiwi.live.system=

Block device to use for the system. By default this is set to /dev/ram0

ramdisk_size=bytes

Size of the ramdisk in bytes. By default this is set to 2097152 (2G)

rd.kiwi.live.reset

Force reset of the live system. This option only makes sense if the live system device (rd.kiwi.live.system) points to a persistent storage device. In this case KIWI NG loads the system only once and does not overwrite it unless a reset is requested.

Persistent Live System

The remote boot process of a live ISO image, places the ISO file into a ramdisk by default. This means all data lives in memory and is not persistent. In order to boot up the live system from a remote location and keep it on a persistent storage, it’s required to pass the rd.kiwi.live.system boot option with the device name pointing to that persistent storage.

Warning

All data on the device given via rd.kiwi.live.system will be wiped

A test based on QEMU is done as follows:

Edit the file /srv/tftpboot/pxelinux.cfg/default and create a boot entry of the form:

LABEL Live-Boot
    kernel boot/linux
    append initrd=boot/initrd ip=dhcp root=live:ftp://IP/image/kiwi-test-image-live.x86_64-1.15.6.iso ramdisk_size=3545728 rd.kiwi.live.system=/dev/sda rd.live.overlay.persistent rd.live.overlay.cowfs=xfs

  • The rd.live.overlay.persistent and rd.live.overlay.cowfs=xfs options are standard KIWI NG live ISO options to control if and how a persistent write partition should be created. The options only take an effect when booting into a persistent storage device.

Next create a persistent storage disk of 3G and attach it to the QEMU instance.

$ qemu-img create mydisk.raw 3G
$ qemu -boot n -hda mydisk.raw

The live system will be deployed once to the locally attached disk and boots from it. Any subsequent boot process will not modify the local disk unless rd.kiwi.live.reset is passed on the kernel command line. If deployed there is also no need for the network anymore and the system could also boot standalone.