Level 1

92 points

External bootable forms of macOS: a few questions

Using Apple articles HT201372 and HT202796 and input from some Forum contributors, I've recently made bootable external forms of macOS, these being the Sierra Installer and Sierra itself. I put these on to separate external USB disks. The idea was, in the one case, to be able to experiment with Sierra whilst still keeping my earlier edition of OSX on my Mac; and in the other case, to be able to install a clean version of Sierra on to my Mac.

But further questions regarding usage of these have now arisen and I'm wondering if someone could advise me accordingly. The questions that have come to mind are:

1. If I now repeat, or partly repeat, the process of putting these on to external disks, could I get away with having them both on the same external disk? Could I put Sierra into one volume (partition) of a single external disk, and the Installer into another partition of that same disk? For the purposes of Restart-Opt and the ensuing disk selection, are you allowed to ever have two bootable entities on the same physical disk? I'm just wondering if I could save having to use two separate external disks.

2. When performing the install from the external disk (I mean a permanent install, not a test switch between Sierra and the former OS), can this be done into the internal disk on the Mac when that internal disk consists of more than one volume (partition)? Normally, you'd need to erase the internal disk before pointing the Installer to it, and so what I'm questioning is whether you can erase just the existing boot partition and leave the other partitions intact.

iMac (27-inch, Late 2013), macOS Sierra (10.12.4)

Posted on May 5, 2017 1:47 AM

23 replies

carefulowner Author

Level 1

92 points

May 10, 2017 4:05 AM in response to Luis Sequeira1

Oops, ok Luis, I bow to your superior knowledge. (I was playing devil's advocate). There are lots of subtle things to learn in this game, isn't there?

Perhaps my choice of words wasn't great. By describing the TM disk as 'bootable' what I meant, of course, was that you can restore an OS, together with all apps and settings, from TM, and that, by definition, what it restores is (once restored) bootable. But clearly, from what you say it'd be daft (and probably impossible anyway) to try to install the new clean OS on to the TM disk. Rest assured, I've taken note.

You say "...... and then elect to migrate your documents from the TM backup". How exactly does that happen? Okay, you've completed the clean install. Presumably, at some point you're then automatically offered the means to migrate your documents, e-mails, etc? And is there a distinction made between apps and general settings on the one hand, and just documents and e-mails on the other, so that you can pick and choose in the way that you've suggested?

May 10, 2017 4:22 AM in response to carefulowner

Perhaps my choice of words wasn't great. By describing the TM disk as 'bootable' what I meant, of course, was that you can restore an OS, together with all apps and settings, from TM, and that, by definition, what it restores is (once restored) bootable. But clearly, from what you say it'd be daft (and probably impossible anyway) to try to install the new clean OS on to the TM disk.

When we use the word "bootable", we mean we can use that disk to run your OS.

That is a big difference: if your drive goes bad (or even if your mac dies), and you have a bootable backup, you can simply hold down option key when you start your (or another) mac, choose the back up drive, and continue working. That is not possible with Time Machine: you have to install and restore.

That is not to diminish the value of Time Machine.

I recommend to have both a Time Machine backup and one (or more) "clones" (bootable backup copies of your working drive). From Time Machine I can fetch an old version of a file that I made changes to or deleted; can't do that with a clone. With a clone I can be up and running in no time even in case of a catastrophic mac failure.

You say "...... and then elect to migrate your documents from the TM backup". How exactly does that happen? Okay, you've completed the clean install. Presumably, at some point you're then automatically offered the means to migrate your documents, e-mails, etc? And is there a distinction made between apps and general settings on the one hand, and just documents and e-mails on the other, so that you can pick and choose in the way that you've suggested?

When you do the OS install, you are asked if you want to import and given the opportunity to select Applications, Settings and Users.

(You can also migrate stuff after the fact by using Migration Assistant, which lies in /Applications/Utilities in your mac)

carefulowner Author

Level 1

92 points

May 10, 2017 6:48 AM in response to Luis Sequeira1

[Don't know what just happened there but somehow I lost my reply to your above comments. Anyway, here's a re-write].

Presumably, to get only my personal documents and e-mails, I'd choose just 'Users'? And it strikes me that if my e-mail folders and their contents are indeed then restored, then by implication the Mail app itself, hitherto configured necessarily manually by me, will be restored at the same time (so, in that respect, some 'settings' will also be restored).

On the matter of TM and the clean install, surely there's nothing to stop you or I from doing an immediate manual TM backup of the new, clean install, once it's in place, on the Mac? Indeed, surely if a TM disk happens to be connected at that time, TM is going to automatically start a full backup of the new install anyway? So, in that sense, you'll thereafter have the clean Sierra always available on the TM disk, until such time as the TM disk runs out of capacity and older backups start to be deleted. Admittedly, though, you'd have had to have installed the new, clean Sierra from an external disk in the first place.

May 10, 2017 6:57 AM in response to carefulowner

The Mail application is part of the System install, so it does not need to be restored.

(so are Safari, Preview, TextEdit, and a lot of other applications that are inherent to the system; every installation of macOS includes them)

If you let Time Machine run *after* you do a clean install, then in principle you may in the future restore to that very point in time and "revert" your system to a clean install.

carefulowner Author

Level 1

92 points

May 10, 2017 8:00 AM in response to Luis Sequeira1

"The Mail application is part of the System install, so it does not need to be restored". Well, the Mail app is clearly part of the System install. However, the e-mail account itself most certainly isn't, not unless I elect to have my e-mail account restored toward the end of, or after, the clean install has completed.

May 10, 2017 8:05 AM in response to carefulowner

carefulowner wrote:

"The Mail application is part of the System install, so it does not need to be restored". Well, the Mail app is clearly part of the System install. However, the e-mail account itself most certainly isn't, not unless I elect to have my e-mail account restored toward the end of, or after, the clean install has completed.

True.

carefulowner Author

Level 1

92 points

May 10, 2017 10:09 AM in response to Luis Sequeira1

Well, I think we've now all discussed my "external bootable forms of macOS" sufficiently for me to now understand how best they should be put on to the disks and how the Installer, in particular, should best be used thereafter. That appears to wrap things up. Once again, my thanks go to you all for being so helpful over this. I've learnt quite a lot.

carefulowner Author

Level 1

92 points

May 8, 2017 8:17 AM in response to Luis Sequeira1

'no interaction' required at the very end of that command line, then?

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External bootable forms of macOS: a few questions