Creating an OS image with Kaniko

It is common to create an OS image with a Containerfile like following:

FROM scratch
ADD rootfs.tar /

However, with Kaniko, /etc/mtab would be missing from the image.

In Kaniko, some predefined paths, including /etc/mtab, are in a ignorelist. If a path is in that list, it will be ignored when taking a snapshot. Currently only /var/run is able to be configured as excluded from ignoring.

On most systems, /etc/mtab is a symlink to ../proc/self/mounts.

A workaround is using a minimal image with such symlink as base instead of building from scratch. We can build that image with a Containerfile like following:

FROM scratch
ADD busybox /
RUN ["/busybox", "ash", "-c", "/busybox ln -s ../proc/self/mounts /etc/mtab && /busybox rm /busybox"]

As there are no instruction to create a symlink, we use busybox for ln. Add busybox in the image, use busybox to create the symlink and delete itself. There is no shell at /bin/sh, so the RUN need to be in “exec form”.