I'm not sure how many people are running Apache on non-server Mac OS X, but if you are and upgrade from Yosemite to El Capitan, you'll get some breakage. The breakage won't be as bad as upgrading from 10.10.4 to 10.10.5 was. Apache generally will still work (as in the server will server up files… Continue reading Fixing Apache after upgrading to El Capitan
If you're using rEFInd on a Mac (for example, if you're dual-booting or triple-booting with a Linux OS), you may have found rEFInd worked fine with Yosemite but broke with El Capitan. This guide worked for me to get it going again: Installing rEFInd on Mac OS X El Capitan.