Francis Drouillard
Level 1 (14 points)
Desktops

Q: iMac (Retina 5K, 27-inch, Late 2015) won't start from USB

Created a bootable El Capitan installer using Terminal and the command "createmediainstaller" per Apple support:

 

Create a bootable installer for OS X - Apple Support

 

My iMac will not start from that USB stick. The progress bar advances to what appears to be completion, then the machine hangs while showing a circle with a slash through it.

 

What's up with that?

iMac (Retina 5K, 27-inch, Late 2015), OS X El Capitan (10.11.5)

Posted on Jun 21, 2016 6:10 AM

Close
Francis Drouillard

Q: iMac (Retina 5K, 27-inch, Late 2015) won't start from USB

  • All replies
  • Helpful answers

  • by mende1,

    mende1 mende1 Jun 21, 2016 6:14 AM in response to Francis Drouillard
    Level 10 (93,324 points)
    Desktops
    Jun 21, 2016 6:14 AM in response to Francis Drouillard

    That circle with a slash means that something went wrong during startup. In order to discard that the OS X El Capitan installer you downloaded was damaged, try redownloading it and creating the bootable USB drive again to see if the issue goes away. Alternatively, you can try an user-friendly app like DiskMaker X to create the USB drive.

     

    Apart from that, it is also possible that you're trying to start up from an unsupported OS X version for your iMac (that may happen if you've not created the USB drive with the latest OS X El Capitan installer).