System console changing to platform-specific defaults

[Benjamin Gilbert]

Hi all,

Over the next couple months, we'll be rolling out a change to the Fedora
CoreOS default console.  The current default depends on the CPU
architecture:

- On x86_64, the first serial port ttyS0 is the primary console and the
  graphical console is secondary.

- On other architectures, Fedora CoreOS generally does not configure a
  particular console, leaving the bootloader and kernel to follow their own
  defaults.  This typically means that a graphical console is used if one is
  available, and a serial console otherwise.

The new defaults will depend on both the CPU architecture and platform.  The
exact configuration is in [1]; in summary:

- On many architecture/platform pairs, Fedora CoreOS will allow GRUB and the
  kernel to follow their own defaults.  On x86_64, this causes the graphical
  console to be selected, even if no video card is available.  In
  particular, *x86_64 bare metal installs will no longer use a serial
  console by default*.

- On platforms that expect specific system consoles to be used, such as AWS,
  Azure, and GCP, Fedora CoreOS will select those consoles by default.

- The QEMU image will continue to select ttyS0 as the primary console
  and the graphical console as secondary.

These changes will be introduced to the Fedora CoreOS `next` stream the week
of October 3, `testing` the week of November 28, and `stable` the week of
December 12.  The changes will only affect new Fedora CoreOS installations;
upgraded systems will retain their current console settings.

If the new defaults aren't appropriate for your environment, you can
override them in several ways:

- For bare metal machines installed with coreos-installer 0.16.0+, use the
  `--console` install option to specify the desired consoles using kernel
  command-line syntax [2].  This will configure both the GRUB bootloader and
  the kernel.  For example, to retain the previous console behavior, install
  with `--console tty0 --console ttyS0,115200n8`.  To customize the
  --console parameter in a live image, use `iso customize --dest-console` or
  `pxe customize --dest-console`.

- For machines launched directly from an OS image, use the Butane
  kernel_arguments section to configure the desired console kernel
  arguments.  For example:

variant: fcos
      version: 1.4.0
      kernel_arguments:
        # Order is significant, so treat these as a single argument
        should_exist: ["console=tty0 console=ttyS0,115200n8"]

Note that this will not affect the consoles used by the bootloader.

- For the unusual case of a virtual machine installed with coreos-installer,
  be sure to use the `--platform` install option to specify the
  virtualization platform, such as `vmware`.  coreos-installer 0.15.0+ will
  automatically configure the default console for that platform.

If the Fedora CoreOS console configuration is important for your
environment, please test the new defaults in the `next` stream after October
6.  If you have any questions or concerns, contact us in #fedora-coreos on
Libera.Chat or open an issue in the Fedora CoreOS tracker [3].

--Benjamin Gilbert, for the Fedora CoreOS team

[1]: https://github.com/coreos/fedora-coreos-config/pull/1781/files
[2]: https://www.kernel.org/doc/html/v4.14/admin-guide/serial-console.html
[3]: https://github.com/coreos/fedora-coreos-tracker/issues/new/choose