Kernel glossary¶

This page is a running list of terminology that is frequently used when talking about kernels.

ABI¶

Application Binary Interface, or ABI defines a stable interface between user space applications and the kernel. It ensures that the binaries of applications compiled for one version of the kernel remain compatible with subsequent versions, as long as the ABI remains unchanged.

DKMS¶

Dynamic Kernel Module Support, or DKMS is a framework that provides support for installing supplementary versions of kernel modules in a simplified manner. See the dkms manpages for more information.

edge kernel¶

An edge kernel is the next HWE kernel still in development with features and/or updates that will be backported from the latest Ubuntu release (until the next LTS).

HWE¶

Hardware enablement, or HWE kernels are Ubuntu kernels based on newer upstream kernel versions (compared to the Ubuntu LTS GA release) that typically contain newer features, improved performance and security, and support for newer classes of hardware. Newer kernels are usually shipped with interim and LTS releases, and will then be enabled on the latest Ubuntu LTS release as the HWE kernel. This provides an easier upgrade path for existing LTS users, and enables new deployments to immediately benefit from the newer kernel version.

See HWE kernels for more information.

linux-meta¶

Refers to a set of meta-packages in Linux distributions like Ubuntu. These meta-packages do not contain the kernel binaries or source code themselves but instead define dependencies that point
to the latest kernel packages. By installing a linux-meta package (e.g. linux-generic), users can ensure they always receive the latest version of a specific kernel series through updates. In the kernel development and SRU life cycle, linux-meta acts as a bridge between the release of new kernel versions and the package manager. When a new kernel version is released and marked stable, the linux-meta package is updated to reference the new version, allowing automatic upgrades.

linux-signed ¶

Refers to kernel packages that are cryptographically signed to ensure their integrity and authenticity. These signatures are crucial for secure boot environments, as they enable the
system firmware to verify that the kernel has not been tampered with and is from a trusted source. In the kernel SRU life cycle, linux-signed is created after the corresponding unsigned kernel (e.g. linux-image-unsigned-6.8.0-50-generic) has been built. The signing process is part of the release pipeline, ensuring compliance with secure boot requirements and enhancing security in the kernel deployment process. This package works in tandem with the linux-meta package to deliver signed kernel updates.

OEM kernel¶

The OEM kernel is an optimized derivative Ubuntu kernel, designed specifically for use in Original Equipment Manufacturer (OEM) projects. OEM kernel variants are typically developed and customized for hardware that will be pre-installed with Ubuntu.

See OEM kernels for more information.

SAUCE¶

A SAUCE patch is a patch not included in Linus Torvalds’ tree or linux-next, either because it hasn’t been pulled in, or because it is obtained from other non-upstream sources and is unlikely to be upstreamed.

See Patch acceptance criteria for more information.

SRU¶

Stands for Stable Release Update, a process in distributions like Ubuntu used to provide important updates to packages, including kernel packages, after the release of a stable version. SRUs deliver fixes for critical bugs, security vulnerabilities, and hardware enablement while ensuring the stability of the system.

unstable kernel¶

The linux-unstable kernel is used for the latest Ubuntu kernel developments. The unstable tree is primarily utilized by the development team and closely tracks the latest mainline kernel releases and SAUCE patches.

Development is conducted in the unstable Git repository on Launchpad.