Either from Heirloom tools, or by running any freeware, open source operating system which is built from the illumos source code, like SmartOS. illumos code bas

Either from Heirloom tools, or by running any freeware, open source operating system which is built from the illumos source code, like SmartOS. illumos code base is the most direct, canonical descendant of AT&T UNIX System V 4.0. If you run anything based on illumos not only are you running a true UNIX, but a reference implementation of it. Additionally, any true System V UNIX like IRIX and HP-UX will have it.