initrd embedding, Debian/Ubuntu CD preseeding

This repository used to contain bash scripts that helped create installer CDs with containing a preseed.cfg, or various files. You can still find those on the bash-scripts branch. They were too restrictive, and a rewrite in Python wasn't worth it. Ultimately, creating these CDs is rare, and doesn't need to be automated. So instead, this repo now contains instructions and a few examples.

1) Acquire the required components

You will need

sudo apt-get install debian-installer-8-netboot-amd64 fakeroot xorriso isolinux syslinux-common

(the last two only necessary if you want to produce CDs).

2) Vanilla installer

mkdir installer
cp /usr/lib/debian-installer/images/8/amd64/text/debian-installer/amd64/{linux,initrd.gz} installer/

3) Customise

The folder extra will contain things that will be added to the initrd.

mkdir extra

For example, a preseed file:

cp /path/to/my/preseed.cfg extra/preseed.cfg

Or, if you wanted to use the network-console (continue installation over SSH; see netinstall-preseed.cfg),

# add our public key to the installer, so we can log in
mkdir extra/.ssh
cp ~/.ssh/id_rsa.pub extra/.ssh/authorized_keys
# generate the installer's host keys in advance, so that we know what the fingerprints are.
# note that the installer will generate new ones for the final system.
mkdir -p extra/etc/ssh 
for type in rsa dsa ecdsa; do
    ssh-keygen -q -t $type -f extra/etc/ssh/ssh_host_${type}_key -N ''
    ssh-keygen -l -f extra/etc/ssh/ssh_host_${type}_key
done

Note: I find it a bit weird that when you log into the network console it starts a new instance of the installer menu rather than just attaching you to the existing one on the terminal. So you may prefer to, instead of logging in as the installer user (whose shell is /bin/network-console), log in as root and use screen -aAx. In particular, this means that if your SSH drops, you're not hosed/split brain.

If your network card requires binary blobs:

apt-get download firmware-bnx2
dpkg-deb --extract firmware-bnx2_*.deb extra/

4) Add extra to the initrd

gunzip installer/initrd.gz
(cd extra; find . | fakeroot cpio --quiet -F ../installer/initrd --append -o -H newc)
gzip installer/initrd

5) Make a CD

At this point, if you can direct boot, then linux and initrd.gz will suffice. Otherwise:

cp /usr/lib/ISOLINUX/{isohdpfx.bin,isolinux.bin} installer/
cp /usr/lib/syslinux/modules/bios/ldlinux.c32 installer/

Copy isolinux.cfg from this repository to installer/isolinux.cfg. Note the comment that enables the serial console, if you intend to install via OOB management / a VM / etc.

xorriso -outdev installer.iso                                \
    -map installer/ /                                        \
    -boot_image isolinux dir=/                               \
    -boot_image isolinux system_area=installer/isohdpfx.bin  \
    -boot_image isolinux partition_table=on