Linux is the free operating system kernel that Linus Torvalds first announced to the comp.os.minix newsgroup on August 25, 1991. In that post, dated 25 Aug 91 20:57:08 GMT, he described “a (free) operating system (just a hobby, won’t be big and professional like gnu) for 386(486) AT clones,” and reported that he had already ported the bash shell and the gcc compiler.
The kernel grew up alongside the GNU project’s tools. Torvalds aimed his early note partly at users of the GNU system, and his postscript stressed that his code was “free of any minix code” and had “a multi-threaded fs.” A kernel by itself is not a usable system, so Linux was combined with the GNU compiler, shell, and utilities to form complete, working operating systems.
Its design was not uncontroversial. In 1992 Andrew Tanenbaum opened a comp.os.minix thread arguing “LINUX is obsolete,” because it used a monolithic kernel tied to the 386 rather than a portable microkernel. The exchange, preserved in the O’Reilly book “Open Sources,” is one of the best-known design debates in computing.
From that hobby beginning, Linux became the kernel that runs the great majority of internet servers and, through Android, the majority of the world’s smartphones, all while remaining free software.