This document serves the purpose of gathering all the useful information regarding the construction of and development of the ubuntu-core flavor.
Every ubuntu-core image is composed of a defined set of snaps. The following section gives a quick overview of what each snap is about and includes a handy list of links for the given project.
New images are composed using the ubuntu-image tool and so called model assertions. In our case, model assertions tell ubuntu-image what to compose the created image of. It is the model that defines the base snap to use, the gadget and kernel. There are different model assertions for 16 and 18, for each supported platform.
The base (core) snap
This is the base filesystem with all the bare-essential libraries and tools for any system to work. Like the core snap, this is required to be present on any 18 core-enabled system. Basically it has to offer any crucial functionality that is needed for a minimal system to function and cannot be easily installed through separate snaps.
- Owner: Foundations Team
core18 for core series 18
LP project: https://code.launchpad.net/snap-core18
Code repository: https://github.com/snapcore/core18
core16 for core series 16
LP project: https://code.launchpad.net/snap-core16
Code repository: https://github.com/snapcore/core16
The gadget snap
Each supported device has its own gadget snap. Gadget snaps are what defines the device, carrying binaries for the bootloader, declaring the partition layout etc.
- Owner: Foundations Team
pi - universal gadget snap for all supported Raspberry Pi devices (pi2, pi3, cm3)
LP project: https://code.launchpad.net/snap-pi
Snap recipe (armhf): https://code.launchpad.net/~canonical-foundations/+snap/pi
Snap recipe (arm64): https://code.launchpad.net/~canonical-foundations/+snap/pi-arm64
Core 18 branch (armhf): https://github.com/snapcore/pi-gadget -b 18-armhf
Core 18 branch (arm64): https://github.com/snapcore/pi-gadget -b 18-arm64
dragonboard - the Dragonboard device
LP project: https://code.launchpad.net/snap-dragonboard
Core 18 branch: https://github.com/snapcore/dragonboard-gadget -b 18
Core 16 branch: https://github.com/snapcore/dragonboard-gadget -b 16
pc - gadget snap for amd64 and i386 devices
LP project: https://code.launchpad.net/snap-pc
Snap recipe 18 (amd64): https://code.launchpad.net/~canonical-foundations/+snap/pc-amd64-18
Snap recipe 18 (i386): https://code.launchpad.net/~canonical-foundations/+snap/pc-i386-18
Snap recipe 16 (amd64): https://code.launchpad.net/~canonical-foundations/+snap/pc-amd64-16
Snap recipe 16 (i386): https://code.launchpad.net/~canonical-foundations/+snap/pc-i386-16
Core 18 branch (amd64): https://github.com/snapcore/pc-amd64-gadget -b 18
Core 18 branch (i386): https://github.com/snapcore/pc-i386-gadget -b 18
Core 16 branch (amd64): https://github.com/snapcore/pc-amd64-gadget -b 16
Core 16 branch (i386): https://github.com/snapcore/pc-i386-gadget -b 16
There following gadget snaps are only used for the 16 series. Even though some of those repositories have 18 branches and/or include some snaps in the 18 track, they do not participate in any of the core18 images and should only be used for core16 (core):
The snapd snap
The snap offering snapd itself. This was once part of the core snap but it has been ripped out as a separate snap since recently.
- Owner: Snapd Team
Code branch: https://github.com/snapcore/snapd
The kernel snap
- Owner: Kernel Team
pi-kernel - the generic Raspberry Pi kernel for all supported Pi devices (pi2, pi3, cm3)
For core16 only (not used for core18), legacy snaps:
pi2-kernel - the generic Raspberry Pi kernel, now renamed to pi-kernel.
One can get the model assertions for the selected supported platform by using the following commands:
Raspberry Pi 2: snap known --remote model series=16 model="ubuntu-core-18-pi2" brand-id=canonical
Raspberry Pi 3: snap known --remote model series=16 model="ubuntu-core-18-pi3" brand-id=canonical
Raspberry Pi CM3: snap known --remote model series=16 model="ubuntu-core-18-cm3" brand-id=canonical
Dragonboard: snap known --remote model series=16 model="ubuntu-core-18-dragonboard" brand-id=canonical
amd64: snap known --remote model series=16 model="ubuntu-core-18-amd64" brand-id=canonical
i386: snap known --remote model series=16 model="ubuntu-core-18-i386" brand-id=canonical
Raspberry Pi 2: snap known --remote model series=16 model="pi2" brand-id=canonical
Raspberry Pi 3: snap known --remote model series=16 model="pi3" brand-id=canonical
Raspberry Pi CM3: snap known --remote model series=16 model="cm3" brand-id=canonical
Dragonboard: snap known --remote model series=16 model="dragonboard" brand-id=canonical
amd64: snap known --remote model series=16 model="pc-amd64" brand-id=canonical
i386: snap known --remote model series=16 model="pc-i386" brand-id=canonical
Promoting snaps to stable
For some cases, the 18 snaps use a special 18 track instead of the default one. This means that for those snaps, instead of channels like stable, candidate, beta, edge there's 18/stable, 18/candidate, 18/beta, 18/edge - especially for gadget snaps. Before attempting promotion from one channel to another, always make sure that you are specifying the right track and channel. Otherwise one might promote a core18-targeted snap to the stable channel used by core16 devices. Look at the list of revisions and available tracks/channels before promotion.
Releasing a new snap to stable:
- Get the list of revisions that are supposed to be promoted for this snap (can be through the snapcraft dashboard).
- Remember that there's a separate revision number for every architecture.
Run this command from your terminal: snapcraft release <snap_name> <revision> <track/>stable
<track/> depends on whether the snap you are promoting has a specific track you want to use, like 18/.
Example #1 (core18 snap): snapcraft release core18 1234 18/stable,18/candidate
Releasing a new ubuntu-core image