mainline kernel
also: upstream kernel, linux-next
The mainline kernel is the official Linux kernel source code maintained by Linus Torvalds and the core kernel developers, representing the primary development line from which all stable and long-term support releases are derived.
The mainline kernel is the canonical Linux kernel repository where new features, improvements, and bug fixes are integrated before being released in stable versions. It serves as the authoritative source code that all other kernel variants are based on.
Development in the mainline follows a predictable cycle: a new version (e.g., 6.0) is released, a 2-week merge window opens for new features, then stabilization occurs through release candidates (rc1, rc2, etc.) before the final stable release. For example, kernel 6.0-rc1 is a release candidate leading to 6.0 final.
Once a mainline version is released, it typically receives bug and security fixes for a few months before becoming obsolete. Users wanting cutting-edge features run mainline kernels, while those needing stability use long-term support (LTS) versions like 6.1.x or 5.15.x, which are maintained separately with backported fixes from mainline.