If you plan to use the OS X installer on other Macs, or—in this case—to create a bootable installer drive, be sure to copy the installer to another drive, or at least move it out of the Applications folder, before you use it to install the OS on your Mac. If you don't, you'll have to redownload the installer from the Mac App Store before you can use the instructions below.
What you need
To create a bootable El Capitan installer drive, you need the El Capitan installer from the Mac App Store and a Mac-formatted drive that’s big enough to hold the installer and all its data. This can be a hard drive, a solid-state drive (SSD), a thumb drive, or a USB stick—an 8GB thumb drive is perfect. Your drive must be formatted as a Mac OS Extended (Journaled) volume with a GUID Partition Table. (Follow this tutorial to properly format the drive.)
Your OS X user account must also have administrator privileges.
Apple’s gift: createinstallmedia
In my articles on creating a bootable installer drive for older versions of OS X, I provided three, or even four, different ways to perform the procedure, depending on which version of OS X you were running, your comfort level with Terminal, and other factors. That approach made sense in the past, but a number of the reasons for it no longer apply, so this year I’m limiting the instructions to a single method: using OS X's own createinstallmedia tool.
Starting with Mavericks, the OS X installer hosts a hidden Unix program called createinstallmedia specifically for creating a bootable installer drive. Using it requires the use of Terminal, but createinstallmedia works well, it's official, and performing the procedure requires little more than copying and pasting.
The only real drawback to createinstallmedia is that it doesn't work under OS X 10.6 Snow Leopard—it requires OS X 10.7 Lion or later. Though it's true that some Macs still running Snow Leopard can upgrade to El Capitan, I think it’s safe to assume that most people installing OS X 10.11 will have access to a Mac running 10.7 or later.
Making the installer drive
- Connect to your Mac a properly formatted 8GB (or larger) drive, and rename the drive
Untitled. (The Terminal commands I provide here assume that the drive is named Untitled. If the drive isn’t named Untitled, the procedure won’t work.)
- Make sure the El Capitan installer (or at least a copy of it), called Install OS X El Capitan Developer Beta.app or Install OS X El Capitan Public Beta.app, depending on which version you’ve downloaded, is in its default location in your main Applications folder (/Applications).