Dual-boot (ElCapitan and Mojave) on a Mac Pro 5,1

dual-bootmojave

I have a 2012 Mac Pro 5,1, running El Capitan. I wish to make it a dual-boot system, El Capitan and Mojave. I understand that I must install High Sierra preliminary to Mojave, and must install a "metal"-capable graphics card (I've purchased, but not yet installed, a Sapphire PULSE Radeon RX 580).

I have my El Capitan system on a 240GB SSD; user directories are on a separate HDD. I've created a 2nd partition on the SSD and done a clean install of High Sierra there. The installer made it an APFS volume, so when I am booted into El Capitan, I cannot select High Sierra as my Startup Disk (El Capitan cannot "see" the APFS volume in System Prefs). I can select High Sierra using the Startup Manager (⌥ Option during startup). But my understanding is that once I install the new GPU (prior to upgrading to Mojave) that the Startup Manager will not work (no boot screen) Thus, once I boot into El Capitan, there is no way to then boot into High Sierra.

Is it possible to resolve this? I've read that it's possible to install High Sierra on an HFS+ partition, but not Mojave. Perhaps I can live with High Sierra and Mojave as my two boot options instead, if I can get my older apps to work on High Sierra? But even then, without a boot screen, it's impossible to get to recovery disks etc (what happens if the boot drive fails?). Is the only option to obtain a GPU that supports the boot screen? Apparently macvidcards.com sell such cards and could modify mine, but they appear very sketchy, from searches I've done.

EDIT: This post may partially be a wild-goose chase – my apologies. I've determined I can probably run all my apps under High Sierra (and possibly under Mojave) – I was mistaken/confused originally – so it's looking like I may not need to boot ElCap anymore. But there may be other users who do need to, so I still think it's a discussion worth having. However, the boot-screen issue remains – in particular being able to boot from recovery partitions or external media.

Best Answer

One possible solution is to install rEFInd Boot Manager. This is free software which can be configured many different ways. Below is a suggested configuration.

By default, rEFInd installs in the EFI partition. You can then configure rEFInd to either boot El Capitan or Mojave. The default operating system to boot can be set directly from the operating system. There is simple AppleScript application you can download which will do this. As example of the application is shown below.

Related Solutions

I erased an APFS Volume containing a second OSX installation (trying out Mojave) but the Mac keeps trying to boot into it

You can change the default to boot High Sierra by either of the following:

Select High Sierra from the Startup Disk pain of the System Preferences application.
Hold down the control key when selecting High Sierra from the Startup Manager.

You still have Mojave code in your APFS container. In your case, do the opposite of the answer you linked to.

BTW: You can also elect to not delete this code. The code will not interfere with the operation of the Mac and occupies very little space.

IN OTHER WORDS:

Note: Below I have assumed APFS Volume "Preboot" is disk2s2 and APFS Volume "My Recovery" is disk2s3.

You can use Disk Utility under High Sierra to remove the APFS volume containing Mojave. However, removing Mojave also requires steps where commands are issued in a Terminal application window. Below are the remain steps needed to remove Mojave.

Open the Disk Utility application.
Get the file system UUID of the High Sierra volume . Right click the icon for the High Sierra volume in the Disk Utility application and select Get Info. Here, I will assume the file system UUID is 2E0E6320-5D0A-4181-B465-ABFF2CBBFC27.
Boot to macOS Recovery.
Open a Terminal application window.
Enter the command below to disable System Integrity Protect (SIP) on next restart.
```
sudo  csrutil  disable
```
Boot back to High Sierra.
Open a Terminal application Window.
Determine the UUID of the deleted APFS Mojave volume. Start by entering the commands given below.
```
diskutil  mount  disk2s2
cd  /Volumes/Preboot
ls
```
The UUID of the deleted APFS Mojave volume should be the same as the name of the directory (folder) that is not the UUID for the High Sierra volume (2E0E6320-5D0A-4181-B465-ABFF2CBBFC27). Here, I will assume this is 832D1AE3-C9F2-454F-BE45-64E1ECBA38AA.

Enter the commands below to remove Mojave from APFS Volume Preboot.

rm  -Rf  832D1AE3-C9F2-454F-BE45-64E1ECBA38AA
cd  ~
diskutil  unmount  disk2s2

Enter the commands below to remove Mojave from APFS Volume My Recovery.

diskutil  mount  disk2s3
cd  "/Volumes/My Recovery"
rm  -Rf  832D1AE3-C9F2-454F-BE45-64E1ECBA38AA
cd  ~
diskutil  unmount  disk2s3

Reset the SIP settings, by entering the command given below.
```
sudo  csrutil  clear
```
Restart the Mac

MacOS – Unable to boot into Mac OSX after updating dual-boot Ubuntu, Partition Type FFFFFFFF-FFFF-FFFF-FFFF-FFFFFFFFFFFF

Usually when the FFFFFFFF-FFFF-FFFF-FFFFFFFFFFFF error occurs, the partition starting and ending values are still correct. I assume this is true in your case. If I am correct, then you need to enter the following commands to change FFFFFFFF-FFFF-FFFF-FFFFFFFFFFFF to 7C3457EF-0000-11AA-AA11-00306543ECAC.

diskutil unmountdisk disk0
gpt remove -i 2 disk0
diskutil unmountdisk disk0
gpt add -i 2 -b 409640 -s 1900925984 -t apfs disk0

The EFI partition (disk0s1) is used occasionally by macOS, so you need to keep this partition. However, Grub files were added to this partition when you installed Ubuntu. The commands below will remove any Grub files that may still exist on the EFI partition . You can enter these commands while booted to macOS.

sudo diskutil mount disk0s1
cd /Volumes/EFI/EFI
rm -rf BOOT
rm -rf ubuntu
cd ~
diskutil unmount disk0s1

To add the free space back to macOS, enter the command given below. You can enter this command while booted to macOS.

sudo diskutil apfs resizeContainer disk0s2 0

Best Answer

Related Solutions

I erased an APFS Volume containing a second OSX installation (trying out Mojave) but the Mac keeps trying to boot into it

MacOS – Unable to boot into Mac OSX after updating dual-boot Ubuntu, Partition Type FFFFFFFF-FFFF-FFFF-FFFF-FFFFFFFFFFFF

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