I'm a bit confused by your post on what you are trying to do here. Are you trying to boot into Recovery Mode to install macOS to an external USB drive or are you trying to boot from a macOS USB installer to install macOS to the internal drive?
Here are the steps I took to create the bootable USB drive (I have a Mid-2014 MacBook Pro with Retina Display): Downloaded the latest OS X El Capitan (10.11.3) from the Mac App Store. Created a bootable USB drive using createinstallmedia (as explained in Apple’s documentation) and it went well. Erased Macintosh HD. Tried booting from USB drive. Go to Download OS and click on OS X El Capitan 10.11. This downloads InstallMacOSX.dmg to your Downloads folder. The next section can only be done on a mac that is capable of running El Capitan. This includes macs that have the potential to run El Capitan but have been upgraded to a newer OS.
Here are the instructions for creating a bootable macOS USB installer:
Make sure to carefully read the section regarding macOS 10.11 as there are extra steps required to extract the real installer from the downloaded .dmg archive to the Applications folder. After running the .pkg file from the mounted .dmg file you can then proceed to use the command line to create the bootable macOS USB installer itself.
Download El Capitan To Usb
/osxlion-56a5d4935f9b58b7d0de9ed7.jpg "Capitan")
Macs are very picky about the drives used for booting a Mac plus the quality of many USB sticks is extremely poor so try using another USB stick especially a different brand.
When erasing the drive make sure to select the whole physical drive within Disk Utility and erase the physical drive as GUID partition and MacOS Extended (Journaled). The physical drive should be the top most item which is usually identified by the make & model of the drive itself.
Mac Create Bootable Usb From Iso
Aug 21, 2021 12:52 PM