I see that stackoverflow is very linux specific. Doesn't unix&linux and askubuntu cover much of the same ground ? I see that unix&linux and serverfault also cater to many Linux server questions. Similarly askubuntu and superuser seems to contain most like questions.
closed as not constructive by hims056, Bo Persson, Lucifer, ChrisF Apr 15 '13 at 8:16
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Context would be useful here.
SE occationally partners with other organisations - AU is pretty much the official ubuntu Q&A site (i'm uncertain if there's a full official partnership). With SU and SF, linux falls under a broader scope that the sites support - SF is for professional sysadmins, and Linux, BSD and Windows all get used inside large organisations. With SU the scope is for personal use hardware and software. Both SF and SU predate unix and linux.
On the other hand, the SE network has many sites with specific topics such as religion (eg judaism and christianity), hobbies (biking and gaming) and so on. Unix and Linux is merely a subset of computers that happens to benefit from its own site.
If you believe that SE has a linux bias, I'd point out this site runs on a windows/IIS/mssql/.Net backend.
If its a matter of too much choice, you obviously need to get to know the site cultures. SF is great if you have a properly difficult question, in a professional environment (but try not to ask anything too basic, or outside a professional setting). On SU, quite a bit goes, and its fairly easy going, and its a good place to ask personal use questions. AU does ubuntu, and nothing else. I'm unfamiliar with UL.
The two specialist sites are relatively unusual, and SU and SF are broad enough for any OS to be supported in their respective context. There's no real linux bias at all.