http://arstechnica.com/apple/2015/06/preview-os-x-el-capitans-first-beta-is-a-promising-heap-of-refinements/4/以下为引用：
System Integrity Protection, also called "rootless," is a new system security feature that prevents the user or any process from writing in system-protected folders. This list includes /System, /bin, /usr (but not /usr/local), and /sbin. Not even administrators can add to these folders or edit files that are in them, though they retain their access to the rest of the files on the drive. That's one way to protect important operating system files from external tampering!
If you never dive into any of those folders, you won't notice the difference in day-to-day usage. If you do, reboot into your El Capitan Mac's recovery partition. There's a new item under the Utilities menu that will let you toggle System Integrity Protection on and off for El Capitan volumes. That's all it does. So we're not looking at an iOS-esque level of system lockdown just yet, though there are no promises that System Integrity Protection won't become mandatory in some future version of OS X.