Change from core24 to core26¶

This is a guide for migrating a snap that uses core24 as its base to core26.

Core26 is built from Ubuntu 26.04 LTS. For most snaps, the migration consists of checking dependencies and extensions. If your snap has strict confinement and runs Python code, you need to add a Python runtime.

Stability and workarounds¶

In the wake of a new core, some of the updated features and packages your snap relies on will be unstable for a time.

This is to be expected with complex software. A short-term fix or workaround in your snap’s parts, packages, and scriptlets might be needed. But sometimes, a temporary fix becomes permanent. It’s a good practice to explain your workarounds with comments in your project’s snapcraft.yaml.

Update the base¶

Start by updating the base key:

snapcraft.yaml¶

- base: core24
+ base: core26

Check extension support¶

Not all extensions are compatible with core26 at its launch. If your snap uses an extension, run snapcraft extensions to see if it’s available for core26. If your snap uses an extension that does not yet support core26, it’s best to wait to upgrade.

Update part names¶

If you update a snap to use core26, then you must also verify its part names. Part names on core26 and later bases can’t contain any forward slashes (/). We recommend replacing them with a hyphen (-):

snapcraft.yaml¶

 base: core26

 # ...

 parts:
-  my/part:
+  my-part:

Update the packages¶

Package names and versions change between Ubuntu releases. If you have parts that declare build-packages or stage-packages, you might need to update those packages in your project file.

Build your snap and note any dependent packages that fail to resolve. Search the Ubuntu package archive for the equivalent on Ubuntu 26.04, and update build-packages and stage-packages accordingly.

A package may have been split, merged, or renamed:

snapcraft.yaml¶

stage-packages:
  - libexample3t64  # renamed from libexample3 in core26

Repackage Python¶

Core26 has updated its Python support commitment, and doesn’t ship with Python. Going forward, all strictly-confined snaps that run Python must pack a separate Python binary.

The optimal solution is to define a separate part, and stage the Python runtime inside it:

snapcraft.yaml¶

parts:
  python-runtime:
    plugin: nil
    stage-packages:
      - libpython3.14-minimal
      - libpython3.14-stdlib
      - python3-minimal # for the "python3" symlink
      - python3.14-minimal
      - python3.14-venv

  my-app:
    after: [python-runtime]
    source: .
    plugin: python

Replace snapcraftctl¶

With core26, snapcraftctl is replaced with craftctl.

In your project file’s scriptlets, find and replace all instances of snapcraftctl with craftctl. For example:

snapcraft.yaml¶

- snapcraftctl pull
+ craftctl default
- snapcraftctl set-grade stable
+ craftctl set grade=stable

Update Spread test systems¶

Snaps should behave the same regardless of the host operating system, but testing on Ubuntu 26.04 may expose failures, such as classically-confined snaps incorrectly accessing host packages.

If your project uses the test command for integration testing, it’s recommended to test your snap with Ubuntu 26.04. Add it to the list of systems in your project’s spread.yaml:

spread.yaml¶

systems:
  - ubuntu-24.04
  - ubuntu-26.04

Retaining older releases in the Spread configuration is recommended.