Alt text:
meme with the 'Always has been' format
Linux, MacOS, OpenBSD and ChromeOS logos on top of the Earth
The first astronaut says 'Wait, it's all Unix?'
A Windows logo, on top of the second astronaut.
The second astronaut says 'Always has been' and points a gun to the first astronaut.
Linux is unix-like, and not from the same family really. ChromeOS is based on linux, so similarly unix-like. Mac is Darwin, which is actually unix. Also all BSDs are unix
Yeah, reading these comments, it looks like they are not legally able to call it unix, despite having direct lineage. Linux however is a complete re-write, making it more obviously not proper unix by most definitions.
Nice to know, I've always thought BSD is actually UNIX.
The BSD variants are descendants of UNIX developed by the University of California at Berkeley, with UNIX source code from Bell Labs. However, the BSD code base has evolved since then, replacing all the AT&T code. Since the BSD variants are not certified as compliant with the Single UNIX Specification, they are referred to as "UNIX-like" rather than "UNIX".
UNIX(tm) is a trademark name (Think of e.g. IBM AIX, HP-UX, SunOS). Linux and BSD are Unix alike. I believe that Apple has made an effort to be entitled to call an OS of theirs UNIX, not sure whether it's Darwin or something else.
More like file descriptor. File path is like address system, but it's not how you get all file descriptors. For example: sockets (there is bash's fake /dev/{tcp,udp}), epoll, timer, event, inotify.
In UNIX systems event systems have a list of filedescriptors with a callback for each. You could have your event loop an epoll fd itself and nest it in another.