outoftree

Outoftree is a term used in software development to describe components that exist outside the main source tree of a project. It typically refers to code, modules, patches, plugins, or extensions that are maintained separately from the project’s official repository. While in-tree components are integrated into the project’s canonical codebase and share its release cycle, outoftree elements are developed and distributed independently, often by third parties or hardware vendors.

In practice, outoftree is most commonly associated with the Linux kernel, where drivers and kernel modules can be provided by manufacturers or third parties rather than being included in the official kernel source. Such modules are built against a specific kernel version and may rely on exported interfaces that change across releases, which can lead to compatibility issues. Outoftree modules may also lack the broad testing and review processes applied to in-tree components.

Advantages of outoftree components include the ability to deliver hardware-specific features, rapid iteration, and vendor control over licensing and updates without waiting for mainline inclusion. However, they can impose maintenance burdens, security considerations, and potential stability risks if not kept in step with the evolving core project.

Maintenance often employs tools such as Dynamic Kernel Module Support (DKMS) to automate rebuilding when the kernel is updated. The lifecycle of an outoftree component may involve eventual upstreaming, where a contributor seeks to merge it into the in-tree repository upon meeting project standards and licensing requirements. See also: in-tree, kernel module, DKMS, patch, firmware.