all unix, linux and other unix-like operating systems are families of computer operating systems derived from the original unix system from at&t bell laboratories. today, the largest unix descendent directly certified as unix is macos by apple. the original commercial unix derivatives included hp-ux, aix and sunos, to name a few. the diversity and perceived incompatibility between various unix systems led to the creation of interoperability standards including the portable operating system interface (posix). we provide free linux and unix shell scripting, system administration and other programming help.