I think that the site dedicated to ‘UNIX & Linux’ shouldn’t have them both as tags since when I am writing on this site, it is already related to what the title of the site says and there is no need to double it in tags.
UNIX, as far as GNU/Linux OS has many different variations, so questions about some basic things (let we rely on POSIX compatibility now) will not be harmed if no
‘unix’ tag will be added to it, they will not clarify the question. There must be a bunch of other details worthy enough to be specified for a good question.
I paid heed to Stack* sites often use many types of notices making a future question more precise. Why not to use a notification that will be shown to a user, looking for a
‘linux’ tag, and asking him to define what exactly GNU/Linux OS his question is related to, and, if it isn’t, say that in that case it is a common question and there is no need in such tag.
Though, topics related to OS kernels should have their tags, and to avoid disambiguation I’d suggest tags like
‘bsd-kernel’ for example. Pay attention to required
‘-kernel’ suffix at the end of the tags. Yes, I already see that tautology in case of
‘linux-kernel’, but since the name of the GNU project is always forgotten, I found this as the most appropriate solution for a Stack* site.
Update starts here.
When you are on StackOverflow it is asking you ‘What is your programming question?’ But there is no ‘programming’ tag. And never will be. Because every question there is about programming, which is category of the common questions. And here we have something common between all the UNIXes and other UNIX-like operating systems, which gives us such category and questions shouldn’t be tagged as ‘unix&linux’ too. Finally the vast majority of packages are widely available not only for GNU/Linux, so with the big share of probability may be related to other UNIX-like operating systems which are not a part of GNU/Linux family. Say I have problems with a gnome-system-monitor on my Fedora. But Gnome DE is available on FreeBSD too, how fair is it to FreeBSD users marking that question with only a
linux tag? I think, it’s not fair. But on the other hand, such problem may be related only for asker’s distro and will never appear in any other GNU/Linux or UNIX/UNIX-like OS because of that distro’s maintainers’ fault or, what is most likely, wrong end-user moves plus a specific distro architecture make the bug unreproducible on the other distro.
So, as far as you can’t say how wide is the range of affected UNIX-like operating systems, it’s convenient to rely upon the category of the common questions. Or if you stand for necessary and proper tag names, almost every topic about e.g. bash or sh should initially have tags like
BSD family, and a whole lot of all GNU/Linux distro names as probably affected.
Or let’s expand the previous example with bash. If a question is related to how to write programs in bash, it is not related to only GNU/Linux and shouldn’t have any ties to any OS (or OS family) by means of tags. But if the question is somehow related to the interaction with OS, that OS (but not the whole family!) should be specified first as a probably local distro bug. If the bug has affected other operating systems, the tag related to specific OS should be removed.
Sorry for my English.