This repository contains source code to build initial ramdisk used in Ubuntu Core Embedded Linux OS.

See: https://en.wikipedia.org/wiki/Initial_ramdisk

In Ubuntu Core, initrd.img file is part of Kernel Snap as a binary. This file is brought to Kernel snap from a PPA. See integration below.

In UC20, initrd is migrated from script based implementation (UC16/18) to systemd based.

On arm SBC's: FSBL-->SBL-->Uboot-->Kernel-->Initrd-->pivot-root to persistent storage root.

On amd64 devices: Bootrom-->UEFI Firmware-->GRUB-->Kernel-->Initrd-->pivot-root to persistent storage root.

TODO: How to explain this in better words?

TODO: Write documentation for how to build initrd locally

See Hacking

When your initrd DEB package is built, you need to perform following steps to make it a part of kernel snap:

TODO: Write documentation for how to integrate initrd.img to your (custom or canonical) kernel

It is possible to enable bootcharts by adding core.bootchart to the kernel command line. The sample collector will run until the systemd switches root, and the chart will be saved in /run/log. If bootcharts are also enabled for the core snap, that file will be eventually moved to the ubuntu-save partition (see Core snap documentation).