Customizing the Root Filesystem

The installer image contains ONBUILD instructions that handle the following:

  • the decompression, and unpacking of the initramfs.xz
  • the unsquashing of the rootfs
  • the copying of new rootfs files
  • the squashing of the new rootfs
  • and the packing, and compression of the new initramfs.xz

When used as a base image, the installer will perform the above steps automatically with the requirement that a customization stage be defined in the Dockerfile.

For example, say we have an image that contains the contents of a library we wish to add to the Talos rootfs. We need to define a stage with the name customization:

FROM scratch AS customization
COPY --from=<name|index> <src> <dest>

Using a multi-stage Dockerfile we can define the customization stage and build FROM the installer image:

FROM scratch AS customization
COPY --from=<name|index> <src> <dest>


When building the image, the customization stage will automatically be copied into the rootfs. The customization stage is not limited to a single COPY instruction. In fact, you can do whatever you would like in this stage, but keep in mind that everything in / will be copied into the rootfs.

Note: <dest> is the path relative to the rootfs that you wish to place the contents of <src>.

To build the image, run:

docker build --squash -t <organization>/installer:latest .

In the case that you need to perform some cleanup before adding additional files to the rootfs, you can specify the RM build-time variable:

docker build --squash --build-arg RM="[<path> ...]" -t <organization>/installer:latest .

This will perform a rm -rf on the specified paths relative to the rootfs.

Note: RM must be a whitespace delimited list.

The resulting image can be used to:

  • generate an image for any of the supported providers
  • perform bare-metall installs
  • perform upgrades

We will step through common customizations in the remainder of this section.