I recommend trying Recovery mode first but if you have reason to try another method, you can do so. Note that if you've come here for help installing rEFInd on a Mac with SIP enabled, you can click to one of the methods in the 'Contents' box to the left of this paragraph. This page is dedicated to this feature, including basic information on why SIP exists, how to install rEFInd on a computer with SIP enabled, and how to use rEFInd to manage SIP. This feature causes some consternation for advanced users, because it restricts what you can do with your computer, even as root. Apple's macOS 10.11 (aka El Capitan) added a new feature, known as System Integrity Protection (SIP), aka 'rootless' mode.
