IGT-20 and IGT-21 was announced years ago. At that time, Debian Jessie was still a “stable” distribution. Thanks to Debian teams, Jessie is now an “oldoldstable” release. It’s very common that new users ask for updated OS version. Technically it’s not difficult. However, due to fact that many users has had their applications running on IGT-20 and IGT-21 with Debian Jessie (Debian 8), it’s not easy for the company to change the default OS release. Here’s an instruction to have your IGT-20 and IGT-21 upgrading from Debian Jessie to Stretch (Debian 9).

Although having upgraded several IGT-20 successfully, I personally strongly recommend that back up your data in case of any unexpected result and use the original IGT-20 and IGT-21 image. And please understand that some configuration might be different after upgrading procedures.

First, ensure there’s no message output from the two commands. Actually, there won’t be any message if you start from the original OS image.

dpkg --audit
dpkg --get-selections | grep hold

If no message was shown, you’re ready to upgrade your system using the following commands. (Update 2020.9.22: some IGT kernels are hold on purpose, it doesn’t stop the upgrading)

mv /etc/apt/sources.list /etc/apt/sources.list.jessie

cat <<_EOF > /etc/apt/sources.list
deb http://httpredir.debian.org/debian stretch main contrib non-free
deb http://httpredir.debian.org/debian stretch-updates main contrib non-free
deb http://security.debian.org stretch/updates main contrib non-free
_EOF

apt-get update
apt-get upgrade

During the upgrade, you’ll be required to resolve some conflicts. I personally answer “Yes”, meaning keep the maintainer’s version instead of the one exists on IGT-20. This is mainly the reason some configuration will be changed, but I think this should have better consistency. It spends some time upgrading. Be patient. When it’s completed, you’re almost done. Enter the following commands. It should not take as much time as the previous step.

apt-get dist-upgrade
reboot

If everything goes smoothly, now you can log in. Use the following command to check the release

lsb_release -a

Here was the output I saw

No LSB modules are available.
Distributor ID: Debian
Description: Debian GNU/Linux 9.11 (stretch)
Release: 9.11
Codename: stretch

By using the same approach, but change the sources.list from stretch to buster, it’s also possible to upgrade IGT-30 and IGT-31 to Debian Buster (Debian 10). Enjoy.