Core20 snap for snapd

This is a base snap for snapd that is based on Ubuntu 20.04

Prerequisites

We recommend an ubuntu installed distribution to develop and test for this repository, with atleast the following installed and available

• Packages: git, snap, qemu-kvm
• Snaps: snapcraft, ubuntu-image, golang

(For a SBC like RPi) you will need UART TTL serial debug cable (Because you will not have SSH in initrd)

Building locally

To build this snap locally you need snapcraft. The project must be built as real root.

$ sudo snapcraft

Testing with spread

Prerequisites for testing

You need to have the following software installed before you can test with spread

• Go (https://golang.org/doc/install or sudo snap install go)
• Spread (install from source as per below)

Installing spread

You can install spread by simply using snap install spread, however this does not allow for the lxd-backend to be used. To use the lxd backend you need to install spread from source, as the LXD profile support has not been upstreamed yet. This document will be updated with the upstream version when this happens. To install spread from source you need to do the following.

git clone https://github.com/Meulengracht/spread
cd spread
cd cmd/spread
go build .
go install .

QEmu backend

1. Install the dependencies required for the qemu emulation

sudo apt update && sudo apt install -y qemu-kvm autopkgtest

2. Create a suitable ubuntu test image (focal) in the following directory where spread locates images. Note that the location is different when using spread installed through snap.

mkdir -p ~/.spread/qemu # This location is different if you installed spread from snap
cd ~/.spread/qemu
autopkgtest-buildvm-ubuntu-cloud -r focal

3. Rename the newly built image as the name will not match what spread is expecting

mv autopkgtest-focal-amd64.img ubuntu-20.04-64.img

4. Now you are ready to run spread tests with the qemu backend

cd ~/core20 # or wherever you checked out this repository
spread qemu-nested

LXD backend

The LXD backend is the preffered way of testing locally as it uses virtualization and thus runs a lot quicker than the qemu backend. This is because the container can use all the resources of the host, and we can support qemu-kvm acceleration in the container for the nested instance.

This backend requires that your host machine supports KVM.

1. Setup any prerequisites and build the LXD image needed for testing. The following commands will install lxd and yq (needed for yaml manipulation), download the newest image and import it into LXD.

sudo snap install lxd --channel=latest/stable
sudo snap install yq --channel=latest/stable
curl -o lxd-core20-img.tar.gz https://storage.googleapis.com/snapd-spread-core/lxd/lxd-spread-core20-img.tar.gz
lxc image import lxd-core20-img.tar.gz --alias ucspread
lxc image show ucspread > temp.profile
yq e '.properties.aliases = "ucspread,amd64"' -i ./temp.profile
yq e '.properties.remote = "images"' -i ./temp.profile
cat ./temp.profile | lxc image edit ucspread
rm ./temp.profile ./lxd-core20-img.tar.gz

2. Import the LXD core20 test profile. Make sure your working directory is the root of this repository.

lxc profile create core20
cat tests/spread/core20.lxdprofile | lxc profile edit core20

3. Set environment variable to enable KVM acceleration for the nested qemu instance

export SPREAD_ENABLE_KVM=true

4. Now you can run the spread tests using the LXD backend

spread lxd-nested

Writing code

The usual way to add functionality is to write a shell script hook with the .chroot extenstion under the hooks/ directory. These hooks are run inside the base image filesystem.

Each hook should have a matching .test file in the hook-tests directory. Those tests files are run relative to the base image filesystem and should validates that the coresponding .chroot file worked as expected.

The .test scripts will be run after building with snapcraft or when doing a manual "make test" in the source tree.

Bootchart

It is possible to enable bootcharts by adding ubuntu_core.bootchart to the kernel command line. The sample collector will run until the system is seeded (it will stop when the snapd.seeded.service stops). The bootchart will be saved in the ubuntu-data partition, under /var/log/debug/boot<N>/, <N> being the boot number since bootcharts were enabled. If a chart has been collected by the initramfs, it will be also saved in that folder.

TODO In the future, we would want systemd-bootchart to be started only from the initramfs and have just one bootchart per boot. However, this is currently not possible as systemd-bootchart needs some changes so it can survive the switch root between initramfs and data partition. With those changes, we could also have systemd-bootchart as init process so we get an even more accurate picture.