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I have just viewed a YouTube video on how to set up my Mac as a Mojave/Catalina dual-boot, using two APFS volumes on the internal drive, instead of using a bootable external drive.

But is there a way to select the boot OS without having to go into System Preferences every time I want to switch? And is there a way that's compatible with the bootable APFS volumes being encrypted?

So far, everything I've seen online about Boot Camp seems to indicate that it's strictly for setting up a Mac/WinDoze dual-boot. Am I mistaken? Can it do what I want here?

By comparison, my DOS/Linux dual boot at home boots to a GRUB menu, that allows me to select the desired OS (PC-DOS 2000 or Ubuntu Hardy Heron), defaulting to whatever OS I used last.

  • Have you tried installing GRUB to dual boot macOS? – David Anderson May 28 at 23:36
  • Yes - Boot Camp is for Windows only. – Seamus May 29 at 9:25
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    You may be able to use systemsetup. It documents -liststartupdisks and -setstartupdisk options, though on my machine (with only one boot disk), -liststartupdisks only displays /System/Library/CoreServices, which looks very much not like a startup disk to me. (Maybe on another machine, it would list something like /Volumes/SomeOtherDisk/System/LibraryCoreServices as well?) – chepner May 29 at 12:41
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You can hold down the ⌥ Option key (also known as Alt) at startup, and that will show you all the available boot volumes.

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    If you hold down the control key when making your selection, then the selection will become the default. – David Anderson May 28 at 20:51
  • I think I remember that, from back when my "bionic desk lamp" iMac at home still had ROMs that could boot the MacOS 9 partition. Thanks to all. – hbquikcomjamesl May 29 at 19:07
9

If you want a boot manger which behaves similar to GRUB, the you could install rEFInd. This free boot manager is similar, because rEFInd can be configured to display a menu of operating system choices for a specified period of seconds, then automatically choose the last used if the period expires.

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    rEFInd is a good recommendation. It was designed & built as a tool for EFI-based machines. The developer knows his stuff. – Seamus May 29 at 9:23
  • I'll research it when I get a chance, although I think the Option key is probably adequate. – hbquikcomjamesl May 29 at 19:07
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There's the bless command, if you're into typing commands. It's here on a 10.12.6 system; don't know if Apple removed it in later releases. Maybe something like:

bless --mount "/Volumes/OtherOS" --setBoot
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    bless is still around, but has been gradually losing most of its usefulness since OS X 10.11, when SIP prevented it from doing anything useful (nor harmful). With EFI boot to APFS drives that is the norm nowadays, bless is very tricky to use correctly, to put it mildly. On systems with the T2 chip, the only useful invocation that I am aware of is sudo bless --info to find out the inode of the booter file. systemsetup -setstartupdisk is what you're supposed to use to set the startup disk from the command line, though I don't think that works on T2 systems either. – kumowoon1025 May 30 at 14:33
  • Ah, ok. Thanks for the insight! – aMike May 30 at 21:40

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