Robert : What does it mean when people say Linux is a unix like OS?

Is there some kind of ratio like 70% based off Unix or 50% based off Unix?


And why base something off Unix? Why not some other kind of platform?

"Unix like" means: It looks like unix when you look under the hood. I.e. file system structure: There are directories like /bin, /usr, /etc, /lib for different kind of files. Other example: The basic command line tools for file manipulation work like their unix siblings.

Windows is completely different.

What we use today is not exactly "based off" unix, it is a complete rewrite.

When I say Unix like, I mean a system that is similar to but not directly related to a true Unix like Solaris or BSD.

With regard to why Linux is Unix like, I guess you'd best ask Linus Torvalds. Or at least look up a bit of the history of Linux. Most 'historic' overviews on the web go into what his motivations were.

GNU/Linux is not "based" on UNIX. These days, UNIX is a trademark of The Open Group, a standards group that, with the IEEE, has published the Single UNIX Specification[1] (which eventually becomes the POSIX standard). (The Austin Group now manages specifications, but The Open Group makes them available.) An operating system that fully complies with these specifications is called a "UNIX" system. Operating systems that come close are called "Unix-like".

Also remember that Linux, which first appeared in 1991, is just the kernel. The other components (the C library, utilities like `ls' and `find', X window server, etc.) were originally either written by or brought together by the GNU project, which started development in 1984. The whole point of the GNU project was to create a free (as in freedom, not price) operating system that was compatible with and nearly identical to Unix, the de facto standard operating system of the time.

Today, most operating systems (GNU/Linux, the *BSDs, Minix, Mac OS X, etc.) are either Unix-like or actual UNIX systems. Clearly, to this day UNIX remains very flexible and powerful. And the SUS/POSIX specifications ensure a level of compatibility between all of these different systems. Why not make an operating system work like UNIX?


[1] You can view and download the SUS version 4 online at no cost, or view it online without having to register.

Well, I would say that should be 'Unix-like' and not 'unix like'. That nitpicking out of the way...

No,that would make no sense. Unix isn't one single thing, with various versions and various releases being slightly different, I don't see how you could calculate a ratio without it being hugely controversial.


It works, it does stuff, even heavy duty stuff and its stable and it is widely used (if you consider the widest definition of Unix) in serious applications. various systems have been based off other systems, but they don't seem to have gained traction. So, a better question might be why basing systems off something else hasn't achieved traction/mindshare?

In general a system is Unix-like, if it feels like Unix to use, it has various characteristics of Unix (filesystem hierarchy, permissions, organisation of processes, common utilities, pipes, links and, I'm sure, more). Broadly, if you know Unix, you should be able to sit down at a Unix-like system and be able to some stuff (and swear at some other stuff), but in general only be stuck with details rather than with everything. .

Thanks for the input guys.