Emergency console access

Sometimes you may want to access the node console to perform troubleshooting steps or emergency maintenance. For instance, you may want to access the emergency shell on the console, in order to debug first boot provisioning issues.

Default console configuration

All Fedora CoreOS (FCOS) images come with a default configuration for the console which is meant to accommodate most virtualized and bare-metal setups. Older FCOS releases enabled both serial and graphical consoles by default. Newer releases use different defaults for each cloud and virtualization platform, and use the kernel’s defaults (typically a graphical console) on bare metal. New installs of Fedora CoreOS will switch to these new defaults starting with releases on these dates:

  • next stream: October 3, 2022

  • testing stream: November 28, 2022

  • stable stream: December 12, 2022

The default consoles may not always match your specific hardware configuration. In that case, you can tweak the console setup. Fedora CoreOS has special support for doing this during bare-metal installation, and in other cases you can adjust kernel parameters. Both approaches use kernel argument syntax for specifying the desired consoles. You can specify multiple consoles; kernel messages will appear on all of them, but only the last-specified device will be used as the foreground interactive console (i.e. /dev/console) for the machine.

Configuring the console during bare-metal installation

If you are installing FCOS via coreos-installer, you can configure the console at install time.

Example: Enabling primary serial and secondary graphical console
sudo podman run --pull=always --privileged --rm \
    -v /dev:/dev -v /run/udev:/run/udev -v .:/data -w /data \
    quay.io/coreos/coreos-installer:release \
    install /dev/vdb -i config.ign \
    --console tty0 --console ttyS0,115200n8

This will configure both the GRUB bootloader and the kernel to use the specified consoles.

Configuring the console with Ignition

If you are launching FCOS from an image (in a cloud or a virtual machine), you can use Ignition to configure the console at provisioning time.

Example: Enabling primary serial and secondary graphical console
variant: fcos
version: 0.15.0
kernel_arguments:
  should_exist:
    # Order is significant, so group both arguments into the same list entry.
    - console=tty0 console=ttyS0,115200n8
  should_not_exist:
    # Remove any existing defaults. Adjust as needed.
    - console=hvc0
    - console=tty0
    - console=ttyAMA0,115200n8
    - console=ttyS0,115200n8
    - console=ttyS1,115200n8

This will configure the kernel to use the specified consoles. The GRUB bootloader will continue to use its previous default. Ignition will configure the console, then reboot into the new configuration and continue provisioning the node.

Configuring the console after installation

You can adjust the console configuration of an existing FCOS node via rpm-ostree.

Example: Enabling primary serial and secondary graphical console
sudo rpm-ostree kargs --append=console=tty0 --append=console=ttyS0,115200n8 --reboot

rpm-ostree will create a new deployment with the specified kernel arguments added and reboot into the new configuration. The GRUB bootloader will continue to use its previous default.