“Rootless” feature is actually a default security protection mechanism in El Capitan, its official name “System Integrity Protection”, which is an overall security policy with the goal of preventing system files and processes from being modified by third parties.
Restart your Mac, and as soon as the screen turns black hold down ⌘R until the Apple logo appears on your screen.
Click on the “Utilities” menu, and then “Terminal”.
Now click on Utilities”, then “Terminal”.
Restart OS X, Your Mac should then restart as normal.
Note: Apple have made the steps to temporarily disable the new security feature SIP (System integrity Protection) in El Capitan quite difficult. It is recommend to only perform these steps if you really must.