I was at Y! from 2004 to 2011, when I started it was FreeBSD only except for acquisitions. When I left it was a mix of FreeBSD and RHEL, with everyone being strongly encouraged to move to RHEL.<p>I think the justifications were better support for running on Linux (storage drivers, Java, MySQL, oracle), better support for virtualization (although bsd jails are better than virtualization in my opinion, and a better fit for Y!), and it would be easier to support one os instead of two and acquisitions (including inktomi) really wanted to run on Linux.<p>The drop dead date for getting off FreeBSD kept getting pushed back, but I&#x27;d guess they&#x27;ve moved almost everything by now.