Updating from CoreOS Container Linux

If you already have CoreOS Container Linux clusters and can’t or don’t want to freshly install Flatcar Container Linux, you can update to Flatcar Container Linux directly from CoreOS Container Linux by performing the following steps.

NOTE: General differences when migrating from CoreOS Container Linux also apply.

The migration script

The update-to-flatcar.sh script does all required steps for you:

# To be run on the node via SSH
core@host ~ $ wget https://raw.githubusercontent.com/flatcar/flatcar-docs/main/update-to-flatcar.sh
core@host ~ $ less update-to-flatcar.sh # Double check the content of the script
core@host ~ $ chmod +x update-to-flatcar.sh
core@host ~ $ ./update-to-flatcar.sh
[…]
Done, please reboot now
core@host ~ $ sudo systemctl reboot

If it fails due to SSL connection issues from outdated certificates, you can also download the update payload of the latest Stable release through plain HTTP and use the flatcar-update script instead:

$ VER=$(curl -fsSL --insecure --ssl-no-revoke http://stable.release.flatcar-linux.net/amd64-usr/current/version.txt | grep FLATCAR_VERSION= | cut -d = -f 2)
$ wget --no-check-certificate "http://update.release.flatcar-linux.net/amd64-usr/$VER/flatcar_production_update.gz"
$ wget --no-check-certificate http://raw.githubusercontent.com/flatcar/init/flatcar-master/bin/flatcar-update
$ less flatcar-update # Double check the content of the script
$ chmod +x flatcar-update
$ sudo ./flatcar-update --to-version "$VER" --to-payload flatcar_production_update.gz --force-flatcar-key

Before you reboot, check that you migrated the variable names as written in Migrating from CoreOS Container Linux .

Going back to CoreOS Container Linux

You can also go the other way.

Manual rollback

If you just updated to Flatcar (and haven’t done any additional updates), CoreOS Container Linux will still be on your disk, you just need to roll back to the other partition.

To do that, just use this command composition:

sudo cgpt prioritize "$(sudo cgpt find -t flatcar-usr | grep --invert-match "$(rootdev -s /usr)")"

Now you can reboot and you’ll be back to CoreOS Container Linux. Remember to undo your changes in your /etc/coreos/update.conf after rolling back if you want to keep getting CoreOS Container Linux updates.

For more information about manual rollbacks, check Performing a manual rollback .

Force an update to CoreOS Container Linux

This procedure is similar to updating from CoreOS Container Linux to Flatcar Container Linux. You need to get CoreOS Container Linux’s public key, point update_engine to CoreOS Container Linux’s update server, and force an update.

Get CoreOS Container Linux’s public key:

curl -L -o /tmp/key https://raw.githubusercontent.com/coreos/coreos-overlay/master/coreos-base/coreos-au-key/files/official-v2.pub.pem

Bind-mount it:

sudo mount --bind /tmp/key /usr/share/update_engine/update-payload-key.pub.pem

Create an /etc/flatcar directory and copy the current update configuration:

sudo mkdir -p /etc/flatcar
sudo cp /etc/coreos/update.conf /etc/flatcar/

Change the SERVER field in /etc/flatcar/update.conf:

SERVER=https://public.update.core-os.net/v1/update/

Bind-mount the release file:

cp /usr/share/flatcar/release /tmp
sudo mount --bind /tmp/release /usr/share/flatcar/release

Edit FLATCAR_RELEASE_VERSION to force an update:

FLATCAR_RELEASE_VERSION=0.0.0

After that, restart the update service so it rescans the edited configuration and initiates an update. The system will reboot into CoreOS Container Linux:

sudo update_engine_client -update