MkLinux

MkLinux (Microkernel Linux) is a discontinued open-source experimental operating system for PowerPC Macintosh computers. It was launched in 1995 as a collaboration between the Open Software Foundation (OSF) and Apple Computer, as a critical pivot in Apple's technical and social history. MkLinux became Apple's first official free and open-source software community project, and the debut of Linux on the first Power Macintosh.

MkLinux's key feature is its microkernel architecture. Most Linux distributions have a monolithic kernel, but MkLinux is distinguished by its architecture which adapted the Linux kernel to run as a user-space server hosted on top of the Mach microkernel version 3.0. This "single server" architecture makes the system stable and easier to debug, but the overhead of communicating with the microkernel reduced performance.

Reception was mixed, focusing on the difficult installation process and the significant performance costs of the Mach kernel. Reviewers noted its potential as a "Unix killer", but that it required users to abandon the user-friendly Macintosh experience for a pure Linux environment. The microkernel's additional technical complexity made tasks like kernel recompilation more difficult compared to standard Linux distributions.

MkLinux was succeeded in the Linux community by the monolithic LinuxPPC. Through the MkLinux alliance, OSF and Apple eventually created the technical substrate necessary to also port the Mach-based XNU kernel to Macintosh. Apple finally resolved its decade-long operating system debacle by adopting the XNU-based NeXTSTEP (codenamed Rhapsody) as the future of macOS.