“Linux is a clone of the operating system Unix, written from scratch by Linus Torvalds with assistance from a loosely-knit team of hackers across the Net. It aims towards POSIX and Single UNIX Specification compliance. It has all the features you would expect in a modern fully-fledged Unix, including true multitasking, virtual memory, shared libraries, demand loading, shared copy-on-write executables, proper memory management, and TCP/IP networking. Linux was first developed for 32-bit x86-based PCs (386 or higher). These days it also runs on (at least) the Compaq Alpha AXP, Sun SPARC and UltraSPARC, Motorola 68000, PowerPC, PowerPC64, ARM, Hitachi SuperH, IBM S/390, MIPS, HP PA-RISC, Intel IA-64, DEC VAX, AMD x86-64 and CRIS architectures.”

[https://www.kernel.org]

The beginning: The Linus Torvalds post to comp.os.minix Newsgroups.
pam_hostscheck: PAM module to control users logon with LDAP authentication + a “host” attribute. Download: 1.2, 1.0
shell_wrapper: Application to allow users have more than one shell (LDAP authentication)