How to make a bootable OS X 10.11 El Capitan installer drive
But to install or reinstall a recent version of OS X, you must either download a non-bootable installer from the Mac App Store or (via OS X’s invisible, bootable recovery partition) download 6GB of installer data from Apple’s servers during the installation process. In other words, you no longer have the same safety net or convenience.
Because of this, I recommend creating your own bootable El Capitan (OS X 10.11) installer drive on an external hard drive or USB thumb drive. If you need to install El Capitan on multiple Macs, using a bootable installer drive is faster and more convenient than downloading or copying the entire installer to each computer. If you want to erase the drive on a Mac before installing El Capitan, or start over at any time, you can use a dedicated installer drive to boot that Mac, erase its drive, and then install the OS (and subsequently restore whatever data you need from your backups). And if your Mac is experiencing problems, a bootable installer drive makes a handy emergency disk.
(OS X Recovery lets you repair your drive and reinstall OS X, but to perform the latter task, you must wait—each time you use it—for the entire 6GB of installer data to download. At best, that’s a hassle; at worst, it’s hours of waiting before you can get started.)
As with previous versions of OS X, it’s not difficult to create a bootable installer drive, but it’s not obvious, either. I show you how, below.
Like all recent versions of OS X, El Capitan is distributed through the Mac App Store: You download an installer app (called Install OS X El Capitan Developer Beta.app or Install OS X El Capitan Public Beta.app, depending on whether you’re installing the Developer Beta or Public Beta, respectively) to your Applications folder. In this respect, the OS X installer is just like any other app you buy from the Mac App Store. However, unlike any other app, if you run the OS X installer from that default location, the app deletes itself after it's done installing OS X.
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.
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.
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.
The Terminal window displays createinstallmedia’s progress as a textual representation of a progress bar: Erasing Disk: 0%... 10 percent...20 percent... and so on. You also see a list of the program’s tasks as they occur: Copying installer files to disk... Copy complete. Making disk bootable... Copying boot files... Copy complete. The procedure can take as little as a couple minutes, or as long as 20 to 30 minutes, depending on how fast your Mac can copy data to the destination drive. Once you see Copy Complete. Done., as shown in the screenshot above, the process has finished.
Createinstallmedia will have renamed your drive from Untitled to Install OS X El Capitan Developer Beta or Install OS X El Capitan Public Beta, depending on which version of the installer you used. You can rename the drive (in the Finder) if you like—renaming it won’t prevent it from working properly.
You can boot any El Capitan-compatible Mac from your new installer drive. First, connect the drive to your Mac. Then, if your Mac is already booted into OS X, choose the installer drive in the Startup Disk pane of System Preferences and restart; or, if your Mac is currently shut down, hold down the Option key at startup, choose the installer drive when OS X’s Startup Manager appears, and click the arrow below that drive to proceed with startup.
Once booted from your installer drive, you can perform any of the tasks available from the OS X installer’s special recovery and restore features. In fact, you'll see the same OS X Utilities screen you get when you boot into OS X Recovery—but unlike with recovery mode, your bootable installer includes the entire installer.