System Integrity Protection
This new security measure is intended to protect OS X – its system files and running processes – from modification, either by malicious software or accident. This has consequences for certain software.
On the more obvious end of the scale, software such as WinClone (twocanoes.com) can still make a backup image of a Mac’s Boot Camp partition easily enough, but when you try to restore the image you might see a warning that System Integrity Protection must be disabled (see http://bit.ly/elcapwin).
Tools whose impact would seem less dramatic are also affected. For example, it’s no longer permitted for processes to attach to system-level ones, so tools like TotalFinder (binaryage.com) can’t piggyback on the Finder to enhance it.
System Integrity Protection can be disabled, though it’s not recommended on a permanent basis. Start your Mac in its Recovery system by holding ç+R at the startup chime. Choose Utilities > Terminal from the menu bar, then enter csrutil disable; reboot. Perform whatever you needed in OS X proper, then return to the Recovery system to re-enable the feature using the command csrutil enable; reboot. If you’re uncertain that you turned System Integrity Protection on again, open Terminal in OS X proper and type csrutil status. Apple’s technical documentation for System Integrity Protection is at http://bit.ly/elcapsip.