Do Facebook's servers run on Linux?

Answer:
Yes. Facebook uses Big-IP 9.4.6, which is an embedded high-speed networking system that incorporates Linux.

Refer to related links below:
In this presentation filmed during QCon SF 2008, Aditya Agarwal (Director of Engineering at Facebook) discusses Facebook's architecture, more exactly the software stack used, presenting the advantages and disadvantages of its major components: LAMP (PHP, MySQL), Memcache, Thrift, Scribe.
Refer to :
http:/www.infoq.com/presentations/Facebook-Software-Stack
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