Use the createinstallmedia command in Terminal to create the bootable installer.Open the Terminal app, which is in the Utilities folder of your Applications folder.You could also use a secondary internal partition. Mount your USB flash drive or other volume.Quit the installer if it opens automatically after downloading. Download the OS X installer from the Mac App Store.Use the 'createinstallmedia' command in Terminal

Have a look at Create a bootable installer for OS X. Make sure you have proper User Data Backups from which to restore your Data before erasing the Macintosh HD. You'll also need to erase the Macintosh HD and perform a clean install. In order to use the Install OS X El Capitan.app from macOS Sierra you need to create a USB Installer and boot the Mac with it. Note: If doing this to downgrade from macOS Sierra. This version of El Capitan can also be installed on MacĬomputers that are not comparable with Sierra. Leopard and would like to upgrade to Sierra, you need to install ElĬapitan first. Who would like to upgrade to macOS Sierra. This version of OS X El Capitan is for users running OS X Snow Leopard Whether or not you've downloaded it in the past, you can now download OS X El Capitan 10.11.6 (6.21 GB) via this link which will open first in the Browser, then in the App Store.

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