Some years ago a customer needed a live ISO containing a customized FAI environment (not for installing but for extended hardware stress tests), but on an USB stick with the possibility to store the logs of the tests on the USB stick. But an ISO file system (iso9660) remains read-only, even when put onto an USB stick. I had the idea to add another partition onto the USB stick after the ISO was written to it (using cp or dd). You can use fdisk with an ISO file, add a new partition, loop mount the ISO and format this partition. That's all. This worked perfect for my customer.

I forgot this idea for a while but a few weeks ago I remembered it. What could be possible when my FAI (Fully Automatic Installation) image would also provide such a partition? Which things could be provided on this partition?

Could I provide a FAI ISO and my users would be able to easily put their own .deb package onto it without remastering the ISO or building an ISO on their own?

Now here's the shell script, that extends an ISO or an USB stick with an ext4 or exFAT partition and set the file system label to MY-DATA.

Examples how to use mk-data-partition

Add a data partition of size 1G to the Debian installer ISO using an ext4 partition
# mk-data-partition -s 1G debian-12.2.0-amd64-netinst.iso

Create the data partition using an exFAT file system on USB named /dev/sdb.
First copy (or dd) the ISO onto the USB stick. Then add the data partition
to the USB stick.
# cp faicd64-large_6.0.3.iso /dev/sdb
# mk-data-partition -F /dev/sdb

Create the data partition and copy directories A and B to it
# mk-data-partition -c debian-12.2.0-amd64-netinst.iso A B

The next FAI version will use this in different parts of an installation. A blog post about this will follow.

A new idea for our Debian installer ISO

Here are my ideas how the Debian installer could use such a partition if it automatically detects and mounts it (by it's file system label):

  • Look for a preseed file and use this (without explicitly specifying it via boot parameters)
  • User could provide its own set of packages that the installer will install
  • d-i could show a menu (like tasksel) and the user can select packages from the data partition
  • Save installation logs onto this partition
  • Provide a postinst script, that is run during the first boot of the newly installed system

The advantage of this approach is that there's no need for the user to remaster the official Debian installer ISO, which is not easy for end users. We only have to extend the installer to use files from this data partition in some portions of the installation. Additional udebs, packages or firmware could automatically be used by the installer. Companies could easily create an OEM installer of Debian.

What do you think about this idea? Please send feedback to