The Ubuntu lifecycle and release cadence

Long term support and interim releases

Version numbers are YY.MM

Releases of Ubuntu get a development codename ('Impish Indri') and are versioned by the year and month of delivery - for example, Ubuntu 21.10 was released in October 2021.

LTS or 'Long Term Support' releases are published every two years in April. LTS releases are the 'enterprise grade' releases of Ubuntu and are used the most. An estimated 95% of all Ubuntu installations are LTS releases.

Every six months between LTS versions, Canonical publishes an interim release of Ubuntu, with 21.10 being the latest example. These are production-quality releases and are supported for 9 months, with sufficient time provided for users to update, but these releases do not receive the long-term commitment of LTS releases.

Interim releases will introduce new capabilities from Canonical and upstream open source projects, they serve as a proving ground for these new capabilities. Many developers run interim releases because they provide newer compilers or access to newer kernels and newer libraries, and they are often used inside rapid devops processes like CI/CD pipelines where the lifespan of an artefact is likely to be less than the support period of the interim release. Interim releases receive full security maintenance for 'main' during their lifespan.

Release components - debs, snaps, images, containers

A release of Ubuntu is made through several different channels. What you consume will depend on where you are and what your interests happen to be.

The heart of Ubuntu is a collection of 'deb' packages which are tested and integrated so that they work well as a set. Debs are optimised for highly structured dependency management, enabling you to combine debs very richly while ensuring that the necessary software dependencies for each deb (themselves delivered as debs) are installed on your machine.

Ubuntu also supports 'snap' packages which are more suited for third-party applications and tools which evolve at their own speed, independently of Ubuntu. If you want to install a high-profile app like Skype or a toolchain like the latest version of Golang, you probably want the snap because it will give you fresher versions and more control of the specific major versions you want to track.

Snaps each pick a 'base', for example, Ubuntu18 (corresponding to the set of minimal debs in Ubuntu 18.04 LTS). Nevertheless, the choice of base does not impact on your ability to use a snap on any of the supported Linux distributions or versions — it's a choice of the publisher and should be invisible to you as a user or developer.

A snap can be strictly confined, which means that it operates in a secure box with only predefined points of access to the rest of the system. For third-party applications, this means that you will have a very high level of confidence that the app can only see appropriate data that you have provided to it. Snaps can also be 'classic' which means that they behave more like debs, and can see everything on your system. You should make sure you have a high level of confidence in the publisher of any classic snap you install since a compromise or bad faith behaviour in that code is not confined to the app itself.

It is also common to consume Ubuntu as an image on a public cloud, or as a container. Ubuntu is published by Canonical on all major public clouds, and the latest image for each LTS version will always include security updates rolled up to at most two weeks ago. You may benefit from installing newer updates than that, but the base image you boot on the cloud should always be the current one from Canonical to ensure that it is broadly up to date and the number of updates needed for full security is minimal.

Canonical also publishes a set of images and containers that you can download for use with VMware or other local hypervisors and private cloud technologies. These include standard Ubuntu images on the Docker Hub and standard images for use with LXD and MAAS. These images are also kept up to date, with the publication of rolled up security updated images on a regular cadence, and you should automate your use of the latest images to ensure consistent security coverage for your users.

Editions, Classic and Core

Each release of Ubuntu is available in minimal configurations which have the fewest possible packages installed: available in the installer for Server, Desktop and as separate cloud images. There are also multiple flavours of desktop Ubuntu corresponding to a number of desktop GUI preferences. All of these images are considered 'Classic' Ubuntu because they use debs as their base and may add snaps for specific packages or applications.

The Ubuntu Core image is an all-snap edition of Ubuntu. It is unusual in that the base operating system itself is delivered as a snap; that makes it suitable for embedded appliances where all the possible apps that might need to be installed are available as strictly confined snaps. Ubuntu Core is an appliance or embedded oriented edition of Ubuntu, not particularly comfortable for humans but highly reliable and secure for large-scale appliance deployments such as IoT and CPE in the telco world.

Ubuntu kernel release cycle

Canonical maintains multiple kernel packages for each LTS version of Ubuntu, which serve different purposes. Several of the kernel packages address the need for kernels with specific performance priorities, for example, the low-latency kernel package. Others are focused on optimisation for a particular hypervisor, for example, the kernel packages which are named after public clouds. You are recommended to use the detailed Ubuntu kernel guide to select the best Ubuntu kernel for your application.

In general, all of the LTS kernel packages will use the same base version of the Linux kernel, for example, Ubuntu 20.04 LTS kernels typically used the 5.4 upstream Linux kernel as a base. Some cloud-specific kernels may use a newer version in order to benefit from improved mechanisms in performance or security that are material to that cloud. These kernels are all supported for the full life of their underlying LTS release.

In addition, the kernel versions from the subsequent four releases are made available on the latest LTS release of Ubuntu. So Ubuntu 18.04 LTS received the kernels from Ubuntu 18.10, 19.04, 19.10 and 20.04 LTS. These kernels use newer upstream versions and as a result, offer an easy path to newer features and newer classes of hardware for many users of Ubuntu. Note however that these kernels 'roll' which means that they jump every six months until the next LTS. Large scale deployments that adopt the 'hardware enablement' or HWE kernels should manage those transitions explicitly. These newer HWE kernels are accompanied by a collection of userspace tools closely tied to the kernel and hardware, specifically X display enablement on newer graphics cards.

The Ubuntu kernel support lifecycle is as follows:

For more information on previous and upcoming kernel releases please see the Ubuntu LTS Enablement Stack wiki page.

OpenStack release cycle

OpenStack release cadence follows Ubuntu release cadence. This means that a new version of OpenStack is released twice a year: in April and in October. Those are shipped with new versions of Ubuntu as packages in the Ubuntu Archive.

However, since Canonical recommends using only LTS versions of Ubuntu in production environments, this limits available OpenStack versions to one by default. Therefore, Canonical maintains an additional archive – Ubuntu Cloud Archive – to provide access to non-default versions of OpenStack on Ubuntu LTS.

As a result, OpenStack versions that are shipped on Ubuntu LTS by default (aka OpenStack LTS versions) benefit from Canonical's commitment around the Ubuntu Archive, including 5 years of standard support and Extended Security Maintenance (ESM). In turn, OpenStack versions which are shipped on Ubuntu LTS through the Ubuntu Cloud Archive are supported by Canonical for 18 months only, except for some versions that are supported for 36 months under Ubuntu Advantage for Infrastructure (UA-I).

Upgrades between consecutive OpenStack versions are fully supported. Users can first upgrade to newer OpenStack versions until the next OpenStack LTS version. Then they can upgrade the underlying Ubuntu operating system. In order to ensure smooth upgrades of OpenStack on Ubuntu, Canonical provides the automation framework based on the OpenStack Charms project.

The OpenStack support lifecycle on Ubuntu can be represented this way:

For more information on supported versions, see Charmed OpenStack documentation.

Charmed Kubernetes release cycle

The release cycles of Charmed Kubernetes and MicroK8s are tightly synchronised to the release of upstream Kubernetes^®. The current release and two prior releases are supported (N-2), subject to changes in the upstream release cycle. Canonical also provides extended security maintenance (ESM) for N-4 Kubernetes releases in the stable release channel.

For Ubuntu Advantage support, users must upgrade to remain in the N-2 support window.

ESM support includes fixes to high and critical CVEs related to Kubernetes charms, limited to the LTS Ubuntu releases in the current N-4 support window. Upstream updates and fixes to Kubernetes binaries or container images are absorbed by Charmed Kubernetes and Microk8s.

The Charmed Kubernetes support lifecycle can be represented this way:

For more information on previous and current releases, please see the Charmed Kubernetes release notes or the MicroK8s release notes.