This is a follow-up of the previous Preseeded Debian Install article, this time to add the capability of asking for a headless install through SSH.

I received every part of my future storage server and needed to install Debian on it. As I did not want to hook up a keyboard and display on it just to install the OS, I looked into the Debian Installer Network Console.

The concept is really simple, as always: The installer can be seeded through the first parts of the installation until the network is available and then let the user continue through SSH.

First I needed to add a new entry in the ISOLINUX menu that can be selected.

cat >> isolinux/txt.cfg <<EOE
label install-stretch-netinstall
	menu label ^Install Stretch $TARGETNAME (netinstall)
	kernel /install.amd/vmlinuz
	append vga=788 initrd=/install.amd/initrd.gz auto=true file=/cdrom/preseed-stretch-netboot.cfg
EOE

For now, the entry is not automatically selected, nor booting automatically if the user does nothing. As this is not really useful for a headless, we need to configure it so that it is automatically selected and boots after a timeout.

Setting a timeout at something more than 0 enables the automatic boot of the default entry. As the Debian ISO ship with no timeout, the script has to set this timeout to something more, such as 5 seconds. As there are multiple files that contains a timeout, I opted for a broad replace in the configuration files. I also deleted the default entry so that our new entry can be selected and executed.

perl -pi -e 's/timeout 0/timeout 50/' isolinux/*.cfg
perl -pi -e 's/\s*menu default//' isolinux/*.cfg

Next I needed to check which questions needed answering and which questions are asked later during the installation. For that I trimmed my generated preseed file from before until the installer got to the network part. I got the following minimal preseed :

d-i debian-installer/language         string   en
d-i debian-installer/country          string   GB
d-i debian-installer/locale           string   en_GB.UTF-8
d-i keyboard-configuration/xkb-keymap select   ch(fr)

d-i netcfg/choose_interface           select   auto

d-i netcfg/get_hostname               string   newdebian
d-i netcfg/get_domain                 string

Then, I needed to enable the Network Console so that I can log into the installer to continue. After looking through some documentations (and some contradictory information), I got the following lines:

d-i debian-installer/language         string   en
d-i debian-installer/country          string   GB
d-i debian-installer/locale           string   en_GB.UTF-8
d-i keyboard-configuration/xkb-keymap select   ch(fr)

d-i netcfg/choose_interface           select   auto

d-i netcfg/get_hostname               string   newdebian
d-i netcfg/get_domain                 string

d-i netcfg/get_nameservers            string
d-i netcfg/get_ipaddress              string
d-i netcfg/get_netmask                string   255.255.255.0
d-i netcfg/get_gateway                string

d-i preseed/early_command             string   anna-install network-console

d-i network-console/password          password install
d-i network-console/password-again    password install
d-i network-console/start             select   continue

Now, once the USB device is inserted, the computer will boot on it, wait 5 seconds for an user input that will not come, execute the Installer passing it the NetworkInstall preseed, configure the first steps and then wait for a user to connect by SSH ssh installer@<IP> with the install password.

The script is available on my Git repository and will be kept updated as needed.