Bootable FAI installer USB stick without ISOHybrid?

Thomas Lange lange at
Mon Feb 1 20:26:42 CET 2021

>>>>> On Mon, 1 Feb 2021 18:08:22 +0100, Alexander Thomas <alexander.thomas at> said:

    > In short: would it be possible to make a FAI installer boot and run
    > from a USB disk that has a normal MBR partition table, instead of the
    > ISOHybrid hocus-pocus?
Sure. FAI does not need an ISO at all. We can already boot from
network and it will be possible to create a boot device using a
different partition layout.

    > contains both a FAI installer and also a partition that is easily
    > accessible and writeable under Windows. It must also be possible to
    > add or at least expand that partition using Windows tools without
    > breaking the ability to boot from it.
Do you want to have one or two partitions the the USB stick?
Since we nee another partition for UEFI maybe you will have three partitions.
Which filesystems are writable by Windows? I guess an ext3/4 partition
is not writeable by default.

    > We don't need the ability to boot from a CD-ROM drive and we don't
    > need to support all kinds of platforms like Macs, we only care about
    > booting a typical modern PC architecture server from USB and running a
    > standalone FAI installer from it. Although legacy boot support with
    > the same disk image would be nice, it would be OK if it only works
    > with UEFI.
For UEFI we need the /boot/efi partition which must be a vfat
filesystem. This contains the boot loader. MBR does not need this
partition. Then we need a partition
for FAI which contains the kernel and initrd and the nfsroot (not sure
if we could use the UEFI partition. This can be a plain filesystem on
a seperate partition or a squashfs (maybe on a vfat).

    > The biggest questions are
    > probably how to do it with minimal changes, and also whether there's
    > anything inside FAI that assumes an ISOHybrid environment and would
    > break when booted differently.
As I said before, ISOHybrid is not needed.
Using fai-cd  -S it will only create a squashfs filesystem. This is
normally booted via network, but maybe a start to create a bootable
USB stick.

Currently I have no time to work on this, but I'm happy to help you.

regards Thomas

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