Change bases

A base snap is a special kind of snap that provides a runtime environment with a minimal set of libraries common to most applications. They’re transparent to users, but they need to be carefully considered when building a snap.

Each base snap is built from a corresponding Ubuntu LTS release. Migrating a snap from one base to the next gives the snap access to newer packages, extended support, and the latest Snapcraft features, including plugins and extensions.

The complexity of the migration process is directly linked to both dependencies in the snap’s project file and the base snap versions being migrated between.

At its simplest, migrating from one base snap to another requires only that the base key is updated:

snapcraft.yaml

- base: core24
+ base: core26

But further changes will most likely be needed. These will depend on the original base and the packages that are bundled with the application.

Update from an old or absent base

Migrating a snap from having no base, or base: core, to core18 or core20, for example, is a more involved process than going from core18 to core20.

This is because building a snap with an old base causes Snapcraft to operate in compatibility mode.

Compatibility mode is essentially an older (2.43-era) version of Snapcraft, and will lose the functionality of newer releases.

Core migration guides

Our core migration how-to guides provide detailed instructions and examples to help you transition your snap between specific bases.

• Change from core18 to core20
• Change from core20 to core22
• Change from core22 to core24
• Change from core24 to core26

Base changelogs

Each base snap contains a changelog at /usr/share/doc/ChangeLog that summarizes the package updates bundled in that release, along with the aggregated updates from previous releases. In the examples below, replace <base> with the name of your base snap (for example, core24).

When the snap is already installed

If the base snap is already installed on the system, the changelog is available at /snap/<base>/current/usr/share/doc/ChangeLog.

You can list all installed revisions and versions of a base with snap list --all <base>. To inspect a specific revision, replace current with the revision number. For example, /snap/<base>/<revision>/usr/share/doc/ChangeLog.

Download a base

You can download a base without installing it, then extract the changelog from it:

snap download <base>
unsquashfs -d <base>-unpacked <base>_*.snap usr/share/doc/ChangeLog

The changelog is then available at <base>-unpacked/usr/share/doc/ChangeLog.