Textbook of Linux

BSD (Berkeley Software Distribution) refers to a series of Unix releases from the University of California, Berkeley, beginning in 1977. Bill Joy and others extended AT&T's Unix with enhancements including the C shell, vi, the Berkeley Fast File System, job control, and a complete TCP/IP networking stack. By the mid-1980s, BSD had become the de facto Unix for universities and research labs, and its TCP/IP implementation became the reference that shaped the early internet.

A long-running legal dispute with AT&T in the early 1990s delayed the release of a fully free BSD, during which window Linux gained traction. When the dust settled, 4.4BSD-Lite emerged as the basis for the modern free BSDs: FreeBSD (general-purpose, server-focused), NetBSD (emphasising portability across architectures), OpenBSD (focused on security and correctness), and DragonFly BSD. Apple's macOS is also partly derived from BSD, through NeXTSTEP and Darwin.

The BSD licence is permissive where the GPL is copyleft: it allows derivative works without requiring them to be free. This difference partly explains why BSD code ended up in many proprietary products (including Microsoft's TCP/IP stack and Sony's PlayStation system software) while Linux code largely did not. For a Linux user, BSD is a sibling ecosystem: similar at the shell, divergent under the hood, and worth knowing about for its rich tradition and some uniquely polished tools.