When Canonical announced its new kernel policy last year to target the latest-possible kernel for new Ubuntu releases, it knew there was a risk: shipping a new stable Ubuntu release with a not-yet-stable Linux kernel.
In the upcoming Ubuntu 25.10 release, this looks set to happen.
Canonical’s Kernel Team has said Ubuntu 25.10 “Questing Quokka” might arrive running on an “unstable” kernel – though “unstable” is a technical not qualitative term; the kernel will be release candidate (RC) status, not a half-baked, glitchy or crash-prone mess!
This is because the Ubuntu 25.10 Kernel Freeze happens on September 25, 2025, while Linux 6.17 is expected to go stable soon after. Ubuntu would have to ship a release candidate (RC) version on the Ubuntu 25.10 ISO since a stable release wouldn’t be available.
The [Canonical Kernel Team] are announcing that Ubuntu 25.10 will potentially be an Unstable Release from the perspective of the kernel and will be henceforth working with that assumption until such time as conditions warrant a change.
Brett Grandbois, Canonical Engineer
Ubuntu has to “freeze” at some point as it needs to package things together, test it, and ship an ISO. The version of the kernel on the ISO won’t change, but users will receive software updates to ‘stabilise’ the RC kernel to its finalised stable form.
Stabilisation Update & Bridge Kernels
Linux kernel RCs are largely feature-complete, and undergo several rounds of testing. Some bugs may linger, and it’s not unheard of for headline features to be pulled last-minute.
Yet by the time a kernel reaches the final release candidate stage, it’s more or less identical to the stable release. It’s often simple a version number change and an “administrative” rubber-stamp that turns a final ‘RC’ to ‘stable’.
If Linux 6.17’s RC proves too rough around the edges, Canonical’s kernel team has a backup plan: ship a “bridge kernel” instead. These ‘bridge the gap’ until the intended kernel is ready.
For Ubuntu 25.10, the bridge kernel would be Linux 6.16, as it’s currently being used in Ubuntu 25.10 daily builds. Bridge kernels would be supported for a few weeks at most, with users updated to the stabilised release kernel (6.17) as soon as possible.
A Big Deal …Over Nothing?
If Ubuntu 25.10 does ship with an unstable kernel or a bridge kernel, the impact for most of us will be minimal. It stills get the same kernel it would have gotten, just a couple of weeks later than originally planned – albeit not on the ISO at all, affecting “live testing”.
Yet, to my mind, having the latest-possible kernel in a new Ubuntu release is worth any schedule-induced road bumps along the way.
Knowing Canonical factored in handling this situation when making its kernel policy change, and knowing it will ensure the intended release kernel is still the release kernel — important to LTS users as they get it through a HWE update — is reassuring.