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Running Mojave on MBP 2014. Just purchased a Samsung T5 SSD 1TB drive and want to run Windows 10 and various other linux distros (Elementary, Mint, Parrot Security, Kali) on it so I could take the drive with me and either boot from my mac or another computer. I got Windows 10 to work by following

https://9to5mac.com/2017/08/31/how-windows-10-mac-boot-camp-external-drive-video/

I was successfully able to boot between Mojave (on MBP HD) and Win10 (External SSD) by holding down Option key as it boots. I then made a bootable USB stick with Elementary OS and booted to that stick. I had already created a partition for the Elementary OS but went ahead and allowed it to partition it the way it wanted to during the install menus. I chose the partition that I had made before to which it changed it to EXT4. Then I created another smaller partition for swap. Once Elementary was installed, it asked for me to reboot. I held down Option and saw my MacOS drive, Windows (External SSD, which was actually the Elementary OS) and then EFI (External SSD, which was the Win10). I tried to boot into Elementary OS and just had a flashing cursor at the top and nothing else. Trying to boot into Win10, it would not get past the choosing where you want to boot from. Like it was locked up. Any ideas on how I can get this to work?

  • Firstly, welcome to Ask Different! :) Can you please edit your question to provide further details. For example, how did you go about installing Elementary? Also, it'd be good to know what you actually mean by "but when I rebooted and held down option, I could not boot into Windows nor Elementary"? That is, what actually happens when you try to boot from them? What do you see? Also – Monomeeth Dec 15 '18 at 4:52
  • I just revised it! – sicksix Dec 15 '18 at 5:29
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A short answer to your question will not fix your problem, but at least you may become more aware of the difficulties installing other operating systems on Macs.

Both Windows and Elementary install their boot files in the hidden EFI partition. When holding down the option key at startup, you invoke the Mac (firmware) Startup Manager. This startup manager does not detect all possible correctly installed operating systems.

The Mac Startup Manager assumes each EFI partition will only contain at most the boot files for a single operation system.

While both Windows and Elementary are using the same EFI partition, you will not be able to use the Mac Startup Manager to boot both operating systems.

Possible solutions are:

  • Use more than one EFI partition. A drive can have more than one EFI partition. Additional EFI partitions do not have to reside at the beginning of the drive.
  • Use a different startup manager. A free startup manager would be rEFInd. I prefer to install rEFInd so this manager can be booted from the Mac Startup Manager, the rEFInd will then allow you to select other operating systems. Actually, rEFInd instructs the Mac firmware to boot the selected operating system.

BTW, I have found difficulty installing most versions of Linux to use an EFI partition other than the default. I usually have to manually move the Linux boot files to an alternate EFI partition. Also, care must be taken to insure any Windows boot files are not overwritten by a Linux installer. The file that usually is overwritten is EFI/Boot/bootx64.efi. This file is copy of the EFI/Microsoft/Boot/bootmgfw.efi file.

You can access any EFI partition from macOS. To access the primary EFI partition on the first internal drive from the Finder, enter the command give below in a Terminal application window.

sudo diskutil mount disk0s1

To unmount, enter the command given below.

diskutil unmount disk0s1

In your case, make the appropriate substitution for your external drive.

Below are the elementary boot files store in the EFI partition. This image was captured from an VirtualBox install. Note: the files EFI/BOOT/bootx64.efi and EFI/ubuntu/shimx64.efi are identical.

b1

  • Thank you David for this information. I had ran into something talking about rEFInd but also saw a comment where someone had said that it screwed up their mac where it would not boot. Do you install rEFInd before you install windows? So bootx64.efi and bootmgfw.efi are one in the same? What does the Linux boot files look like? – sicksix Dec 15 '18 at 6:15
  • I prefer to install rEFInd in a small (~200 MB) FAT formatted partition. (This is NOT a EFI partition.) I choose this because I do not have to disable SIP to install. You will be able to select rEFInd as the default from the Mac Startup Manager. Also, the files are accessible from all installed operating systems. This makes it easier to configure rEFInd. Will the other computer you mention in your question also be a Mac? I am assuming so. – David Anderson Dec 15 '18 at 6:26
  • Dang you answered in time! :) I was just about to disable SIP! I am going to make a small FAT partition and do that very thing! Well I wanted to be able to boot the drive from any sort of computer but if that would not work, I am fine with just my mac.. – sicksix Dec 15 '18 at 6:29
  • You install rEFInd as soon as you create a FAT formatted partition. (You can also create the USB flash drive version, if you want to try rEFInd without actually installing to a HDD or SSD.) The files bootx64.efi and bootmgfw.efi are identical but each copy is stored in a different folder. I could post the exact elementary boot files, but it would take about 20 min to setup in VirtualBox. – David Anderson Dec 15 '18 at 6:31
  • I bet I could find those boot files somewhere on the ole Googles! :) I appreciate your help David! I am gonna work on this for a bit and see what I come up with! – sicksix Dec 15 '18 at 6:43

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