Flatcar Container Linux update.conf specification

    Flatcar Container Linux uses update_engine to check and fetch new updates from the Nebraska Update Service .

    Location

    The client-side configuration of these updates is stored in /etc/flatcar/update.conf. (there is a legacy symlink of /etc/coreos -> /etc/flatcar for compatibility with third-party integrations). This file is in the user writable partition by default.

    Next order of client-side configurations that are checked are:

    • /usr/share/flatcar/update.conf
      • Generated at build time of the image/payload build
      • will typically contain:
        • SERVER=
        • GROUP=
    • /usr/share/flatcar/release
      • Generated at build time of the image/payload build
      • will typically contain:
        • FLATCAR_RELEASE_VERSION=
        • FLATCAR_RELEASE_BOARD=
        • FLATCAR_RELEASE_APPID=

    Fields

    Default installs of Flatcar will likely not need custom settings, and an empty or non-existing /etc/flatcar/update.conf file is sufficient.

    • GROUP
      • The channel/group this host will pull updates from
      • public channels will be: stable, beta, alpha
      • otherwise these are UUIDs
    • SERVER
    • FLATCAR_RELEASE_VERSION
      • The current version of this machine
    • FLATCAR_RELEASE_BOARD
      • The board build is determined by the architecture of the machine
    • FLATCAR_RELEASE_APPID
      • The Flatcar specific application ID
      • For Flatcar this is: {e96281a6-d1af-4bde-9a0a-97b76e56dc57}
    • PCR_POLICY_SERVER
      • Server to receive the POST'ed TPM PCR Policy
    • DOWNLOAD_USER
      • Authentication user for fetching the update payload
      • As the update server can redirect to a payload download that may require its own authentication
    • DOWNLOAD_PASSWORD
      • Authentication password for fetching the update payload
      • As the update server can redirect to a payload download that may require its own authentication
    • MACHINE_ALIAS
      • Optional human-friendly name for the machine in addition to the machine ID from /etc/machine-id, to be displayed in the update server UI, should be unique but this is not enforced
      • Set this dynamically by running, e.g., sudo sed -i "/MACHINE_ALIAS=.*/d" /etc/flatcar/update.conf ; echo "MACHINE_ALIAS=$(hostname)" | sudo tee -a /etc/flatcar/update.conf for the output of the hostname command (as with the other variables, restarting update-engine.service is not needed)

    (for future-proofing, calling git grep GetConfValue\(\" in the update_engine repo)