The standard Debian installer disks are quite flexible in what options they support, but much of these features require you to either manually type a number of options at the bootloader prompt or do use a preseed config file.
The preseed config is quite easy to use in a large environment where you can either control the boot network settings and serve up the preseed file. However, even in that scenario, there is often not quite enough control of the network environment to be able to seamlessly configure the location of the preseed.
There are multiple projects for building an entire Debian installer system and there are several tutorials on how to edit an existing Debian installer image, however I found it simpler to have a tool that I could use to make minor changes to an existing installation CD image.
Specifically, this tool can append a new (or replacement) preseed config to an existing installer image.
The makefile has two helper targets that can be used to quickly do some manual testing on the generated images.
- First, ensure you have the right packages
make build-dep - Run a test booting via legacy bios
make test_qemu_bios - Run a test booting via UEFI
make test_qemu_efi
If the re-packed installer image has been configured for a network install, the VM started during these tests exposes the guest SSH port on port 4022, so you can ssh into the installer environment and test that.
- create btrfs with correct subvolume