Question: A few seconds ago a first time user of AU asked a question (on AU), which was promptly and correctly [answered](https://askubuntu.com/questions/794013/what-is-in-terminal-command-line) by @terdon. That question had an [exact dupe](https://unix.stackexchange.com/questions/11376/what-does-double-dash-mean-also-known-as-bare-double-dash), equally well answered by @Guss, earlier on Unix & Linux, a SE communities with *some* overlap with AU and a few other SE communities.

Initially I was actually real surprised that said question was not already answered on AU; on second thought it actually *made sense* since it already had at least one excellent answer on Unix & Linux. 

It *made sense*, **but** I would not go as far as saying that before making a query on AU, one should first check whether there is an answer for it in a different SE community. Rather one should learn to post in the right community to begin with. Right, but sometimes it's not so easy to decide as in this case.

* So, how should one treat a query in a community A, which was already posted in unequivocal terms in community B, both on SE ?
* Should one call that a dupe or a "cross-dupe", without meaning that the two communities are one but somehow closely related ? I am not sure that sounds completely right.
* Should flair be awarded per usual, either through upvotes or automatic increment upon acceptance of such an answer to a cross-dupe ?
* Or should the query echoing another identical query in another community of StackExchange be treated differently in terms of flair accrual, categorisation as dupe, removal, etc. ?

Answer: 
Personally, I think that the best solution would be to develop a way of sharing questions across all sites where they're on topic. The rules against cross-posting were developed back in the days when there was very little overlap between the subject matter of different SE sites. However, things are very different today. The question you mention would be on topic here, on [Unix & Linux](https://unix.stackexchange.com/), on [Ask Different](https://unix.stackexchange.com/), [Super User](https://superuser.com/), [Elementary OS](https://elementaryos.stackexchange.com/) and maybe more. The current system would allow duplicate questions and duplicate answers across all of these sites. 

While I quite agree that this is less than optimal, it's the way things are at the moment. There is no way of flagging cross-site duplicates and no actions mods can take even if such a flag were raised. If you know that the same question has been asked and answered elsewhere, you can feel free to copy it verbatim and post it as an answer here. It would be polite to include a link to the site where you found it, of course, but copying SE answers is very much allowed. We had a discussion on [Unix & Linux meta](https://unix.meta.stackexchange.com/q/1396/22222) a while ago and that was the conclusion there as well. 

So, no, don't flag and yes, copy the existing answer. If you want to be super nice, you can make it [Community Wiki](https://askubuntu.com/help/privileges/community-wiki) so as not to get points for other people's work but, again, that's completely up to you.
I think a lot of the confusion arises from forums that are very similar. In some cases, a question is on topic in more than one community. In that case, I believe that exact duplicates **should** stay. I have basically two reasons:

1. Web presence
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If the question is correctly answered in two places, the answer will be easier for people to find straight from the search engine or even straight on the site. In other words, whether a person is searching Google for an answer to a question or searching a particular StackExchange community, they will find the information.

2. Bigger database
==================

It also gives each stackexchange communtiy a larger database of information to draw from in the future, preventing further confusion. That is to say, even if you were somehow able to close all these remotely duped questions, sooner or later, it's going to pop up again and you'll have to do it again. Wastes time: poor moderators.

All that being said, I have seen situations arise in which a question is questionably on topic but and is already correctly answered in a community where it is unquestionably **on topic**. In these cases, my humble opinion is that there should be a means of migrating and duping. Otherwise, it simply promotes re-asking questions in the wrong place; thus promoting disorder and cheating the system.