It turned out that booting Linux from a USB flash drive / USB pen drive / USB stick (or CD for that matter) is nearly impossible without rEFIt or its modern clone, rEFInd. Google found solutions that may work for more modern Macbooks (pro), but not for this machine. One of them includes Booting the Mac from such a device. Reasons for Mac Boot from USB. Booting the Mac from USB in a way gives the power back to the user. The likeliest of the reason for choosing the boot from the USB method is that your Mac won't start which denies the user access to the computer. N: Start up from a NetBoot server, if your Mac supports network startup volumes. To use the default boot image on the server, press and hold Option-N instead. Disabled when using a firmware password. Command-S: Start up in single-user mode. Disabled in macOS Mojave or later, or when using a firmware password. T: Start up in target disk mode. Also, have you confirmed that your 2009 (10 year old) mac is capable of booting macOS 10.13? After 6 years, Apple stops supporting updates on most older hardware, so you may be unable to boot the High Sierra USB due to that OS not supporting your 2009 Mac.

Hi

I have been trying to reinstall macOS on my MacBook Pro 13 (2015) and for reasons I still don't know, the bootable USB I created was not showing up when I booted into the Startup Manager (by holding the option/alt key).


Mac Not Booting From Usb

I tried creating the USB via both diskmarkx and Terminal. But neither was helping me. Then I tried several fixes and this one finally solved the problem. For any of you out there facing the same problem, this might help.


Mac

Steps :

1. Reset PRAM of your machine by holding option+command+P+R keys together soon after you press the Power button and hear the startup chime.

2. Hold the keys until the grey screen goes off completely (the machine should be restarting).

Mac Not Booting From Usb Flash Drive

3. At 'this' point, insert the Bootable USB Disk you created and press and hold the option key.

4. Hold the option key until you see the Startup Manager.

From

Mac Not Booting From Usb


Hopefully your USB should be listed as one of the bootable disks in the Startup Manager.

Mac not booting from usb mac

MacBook Pro with Retina display, OS X El Capitan (10.11)

Posted on Feb 21, 2017 6:29 AM