@fra-san this is a complicated issue. For reasons that I personally have never understood, the U&L community absolutely hates cross posts. More than any other place on the network and to the extent that we even have a dedicated close reason or this. So cross posted == off topic here. Period.

I don't really agree with this myself, but the community has spoken.

On a more personal note, what I usually do is check if either post is better (has answers, more info, useful comments or whatever). If the one here is better, I'll leave it open and flag the one on the other site letting the local mods know it's a cross post. If the other one is better, I just close ours.

@terdon Thanks! At least there is clear guidance on what would never be considered the wrong course of action.

@terdon Yeah, I was just about to repeat your own concerns...

What makes me feel uncomfortable is that the OP is usually unaware of what's going on. In the (from the community POW) ideal case, they see all their post closed, possibly after having been suggested to post to a different site.

I know...

Ideally suggestions to post elsewhere contain the keyword "instead"

That part is quite complicated too: IMO the suggestion should be "I'm voting to migrate this to <site>" if a migration path exists; "You should flag for mod and ask for this to be migrated to <site>" if a migration path does not exist and the site's mods agree with this course of action and there is no risk of migrating crap; "You should delete this and re-post it on <site>" if the Q can be deleted and other options don't apply;

"You should post this on <site> and make sure you cross-link both Qs, possibly explaining why you multi-posted it (and don't worry if you see it downvoted and closed)" otherwise.

Hardly something we can expect from the average user that tries to be of help.

Yeah...

@terdon Isn't cross-posting contrary to SE policy in general?

@FaheemMitha Yes. But we're the only site that is so dead set against it we have an actual dedicated close reason for it.

@terdon I see. That's surprising. But does it make a difference in practice?

@FaheemMitha Does what make a difference in practice? That we have a dedicated rule? Of course, this means that people use the rule to close the question.

On one hand, given the available tools on SE, a "put on hold all the copies" → "reopen where appropriate" cycle may be a good way to deal with multi-posting. And a dedicated close reason is probably useful in this light.

A far, far better solution would be a system allowing sites to share questions.

There are too many sites with overlapping scopes these days.

How can I know if the expert who can answer my shell question hangs out on Unix & Linux, Stack Overflow, Super User, Ask Different, Ask Ubuntu, elementary OS or somewhere else?

@terdon Totally agree, having the option to share (and un-share, if a site's community finds it off-topic) a question would be smoother and save a lot of work.

But I also see a point in the counter-argument that sharing the answers is much more problematic.

Yes. It isn't a trivial thing to do.

And how would the votes work, and how would you deal with different local requirements for good vs bad questions...

I just feel that the blanket ban on crossposting is also not a good solution.

@terdon an ideally informed user can start posting on each, wait to see if they get an answer. After a week of tumbleweed they can delete and try the next. If they reach the end of the list they can choose one, post there and bounty it :P

Yeah. Not a waste of anyone's time and energy at all! :)

no, that was not part of the optimization process

Surely this is a complex subject. To keep things simple, my aim was to focus on the issue of users that see their questions closed, possibly downvoted, possibly with comments saying "cross-posted here", when they just re-posted a question on a second suitable site because it got no attention on the first one.

The policy says "close on sight". And I was wondering what we can do for them.

Close on sight. Oh, you mean for them, nevermind :P

@fra-san The best I've come up with is leaving a comment along the lines of "Sorry, but we have some surprisingly strict and rigid sets of rules against posting on multiple sites here. I know it's strange, but please choose just one site and post your question there".

Something that explains and also apologizes for the draconian strictness.

A bullet with a smiley engraving :)

(it makes absolute sense)

@AndrasDeak To be honest, I don't think a few questions posted on two sites would devastate the network :-) (That's why my focus is on OPs here).

Of course real spam is a different thing.

@AndrasDeak it would. Migration sucks.

1) most users of one site don't know enough about the scope of the target site to migrate correctly; 2) people tend to use migration as a way of removing crap they don't like without checking if the target is better; 3) based on the flags I handle, many people here don't know our scope and want to migrate away perfectly on topic questions;

4) it is better for everyone, especially the OP, to just delete the question and repost instead of migrating: when you migrate, the question keeps the original date so it doesn't appear first on the /questions page.

@terdon OK. I'm generally fine with explaining. I just hoped there was a more efficient/shared way. Anyway, thanks.

@fra-san Hey, I'm with you. I wish we could find a better way.

I honestly don't see any problem with cross posts either. I would just link them all so any answer posted on one site can be seen by the others. And maybe make the accepted answer propagate across sites...

@terdon yeah, I can see those

for every migration vote I make on SO I leave 100 comments telling people not to suggest posting on Code Review automatically

@terdon Yeah, a dedicated kind of link would probably do a lot.

@terdon I didn't know that!

but I guess it makes sense in terms of the engine

@terdon well fragmentation of information can be a problem. And if you google the problem (ideally in line with the title) and you see 3 copies on 3 different sites with 3 sets of answers... that's not great either

I usually get redundant hits in duckduckgo and I might not even notice that two copies are from two different SE sites

Yeah. On the other hand, this is fragmentation: you never know what site the answer might be found on.

But yes, there is no silver bullet solution.

@terdon that's what search engines are for

Alternatively, sites could agree on shared tags and make questions cross-visible (without duplicating nor moving them). I suspect no one would be happy with such a proposal, but to me it'd make sense :-)

Ah! This exists already (almost): stackexchange.com/filters

@fra-san huh! I hope it's not as good as the internal search engine...