Build an image with custom snaps
An Ubuntu Core image is built using the ubuntu-image command with a signed model assertion:
ubuntu-image snap ubuntu-core-20-amd64.model
See Build your own Ubuntu Core image for more details on the entire process.
ubuntu-image tool retrieves signed snaps with the given snap-id in the model assertion from the store. To override these default snaps, first make sure the model assertion has a grade of dangerous to allow non-store snaps to be included:
grade: dangerous
The ubuntu-image command will now build an image using locally sourced and built snaps, such as a custom gadget snap:
$ ubuntu-image snap my-model.model --snap ./pc_20-0.4_amd64.snap
WARNING: proceeding to download snaps ignoring validations, this default will change in the future. For now use --validation=enforce for validations to be taken into account, pass instead --validation=ignore to preserve current behavior going forward
Fetching snapd
Fetching pc-kernel
Fetching core20
WARNING: "pc" installed from local snaps disconnected from a store cannot be refreshed subsequently!
Copying "./pc_20-0.4_amd64.snap" (pc)
You can now use the image to boot either real or virtual hardware. From within a running session on a custom image, you can run the pre-installed snap:
htop
Use snap list to see which snaps are installed:
$ snap list
Name Version Rev Tracking Publisher Notes
core20 20 634 latest/stable canonical✓ base
htop 3.0.2 1332 latest/stable maxiberta -
pc 20-0.4 108 20/stable canonical✓ gadget
pc-kernel 5.4.0-54.60.1 642 20/stable canonical✓ kernel
snapd 2.47.1 9721 latest/stable canonical✓ snapd
The snap model --assertion command will show the read-only custom model assertion used to build the image:
$ snap model --assertion
type: model
authority-id: bJzr2XzZg6Qv6Z53HIeziXyxtn1XItIq
series: 16
brand-id: bJzr2XzZg6Qv6Z53HIeziXyxtn1XItIq
model: ubuntu-core-20-amd64
architecture: amd64
base: core20
grade: signed
snaps:
-
default-channel: 20/stable
id: UqFziVZDHLSyO3TqSWgNBoAdHbLI4dAH
name: pc
type: gadget
-
default-channel: 20/stable
id: pYVQrBcKmBa0mZ4CCN7ExT6jH8rY1hza
name: pc-kernel
type: kernel
-
default-channel: latest/stable
id: DLqre5XGLbDqg9jPtiAhRRjDuPVa5X1q
name: core20
type: base
-
default-channel: latest/stable
id: PMrrV4ml8uWuEUDBT8dSGnKUYbevVhc4
name: snapd
type: snapd
-
default-channel: latest/stable
id: hJmReLmgXSUj4SF7WhyTVRV6IzUa4QUZ
name: htop
type: app
timestamp: 2020-11-17T13:09:51+00:00
sign-key-sha3-384: 9aZR3b1U[...]