A kernel in continuous evolution
The Linux kernel 2.6, first released in December 2003, represents a paradigm shift that is both technical and organisational. With the 2.6 series the project abandons the old development model based on stable and unstable branches (even and odd version numbers) in favour of a time-based release model: a new kernel version is released every two to three months, with a predictable cycle of merge window and stabilisation period.
This model, made possible by the adoption of Git as the version control system, has greatly accelerated the integration of new features while maintaining stability. Each release brings incremental improvements instead of accumulating them over years into a single major release.
Architectural innovations
The 2.6 kernel introduces a series of innovations that transform Linux into an operating system ready for enterprise workloads:
- O(1) scheduler: the process scheduler, rewritten by Ingo Molnar, guarantees constant decision time regardless of the number of active processes. This is critical for servers managing thousands of concurrent threads
- NPTL (Native POSIX Thread Library): the new thread implementation, developed by Ulrich Drepper and Ingo Molnar, replaces the old LinuxThreads. NPTL provides POSIX-compliant threads with drastically reduced creation and context switch costs — a single system can now manage tens of thousands of threads
- SELinux (Security-Enhanced Linux): the Mandatory Access Control framework developed by the NSA and integrated into the kernel. SELinux enforces granular security policies that restrict what each process can do, even when running as root
- Device mapper: a framework for mapping block devices that enables LVM (Logical Volume Manager), software RAID and disk encryption at the kernel level
- FUSE (Filesystem in Userspace): allows implementing file systems in user space without modifying the kernel, paving the way for experimental file systems and solutions such as sshfs
Linux everywhere
In 2008 Linux is no longer just the operating system of developers’ workstations. The 2.6 kernel runs in the data centres of the world’s largest companies, is the dominant operating system in supercomputers — over 80% of the TOP500 list runs Linux — and powers a growing number of embedded devices: routers, NAS appliances, media players, mobile phones.
Enterprise distributions such as Red Hat Enterprise Linux and SUSE Linux Enterprise Server offer commercial support, hardware certifications and multi-year maintenance cycles. The maturity of the kernel, the predictable release model and the breadth of hardware support have made Linux the default choice for server infrastructure.
Link: kernel.org