There isn’t any single “official”
man location on the web.
The single best source of information for you is the man pages available on your system. These will actually match the versions of the programs, interfaces etc. they document; this won’t be the case for man pages on the web (or rather, it will be up to you to figure out whether man pages on the web match your system). In some cases, your installed man pages will lack information; you might find other sources of information on your system (e.g. Info pages for GNU programs), or you might need to look at more recent man pages, or ask questions here.
As far as web pages reproducing man pages, there are a variety of them:
- some projects make their man pages available on the web themselves; for example,
- some distributions make the man pages they ship available on the web; for example, Debian, Ubuntu, OpenBSD;
- a number of “aggregators” publish collections of man pages; this includes Michael Kerrisk’s man7.org, which is probably the most up-to-date as far as Linux documentation is concerned.
Note that in man7.org’s case, some of the man pages presented are aggregated from other projects, and some are the result of the man-pages project’s efforts. In particular, man7.org hosts the documentation for Linux system calls, so it is the canonical reference for those. However the web site publishes the latest released version of the man pages it presents, so they might document features which aren’t available on your system (for man pages from the man-pages project itself, this should be clear in each document).
For some variants of Unix or Linux, you won’t find man pages online. Apple for example used to host macOS man pages, but no longer does.