Workaround for sudo not working in OS X EI Capitan 10.11.4

The sudo command does not work when the Mac is upgraded to OSX EI Capitan 10.11.4, and any action is always displayed operation denied. This is due to the introduction of the rootless mechanism in 10.11.4, that is, even if the root user cannot read or write to certain files or directories, only Apple or Apple-authorized signed software can. The scope of the rootless includes:

/system

/bin

/sbin

/usr

The way to turn off rootless is to restart your Mac, and when you restart, press and hold Command+r, and when your Mac starts, select Utilities->terminal at the top of the menu bar and enter the following command:

Csrutil Disable

Restart the Mac again after running the command.

Workaround for sudo not working in OS X EI Capitan 10.11.4