Catalina dual boot with (now) Mojave — Users, iCloud etc, to simplify reversing course?

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Catalina dual boot with (now) Mojave — Users, iCloud etc, to simplify reversing course?

I use an MBP 2015 with Mojave 10.14.6 on a 512GB SSD/APFS, and an MBP-2010 with High Sierra 10.13.6 on a 256G SSD/APFS. Both are logged in to the same iCloud user ID, and both use the same DropBox account.

I'd like to install and run Catalina in an easily-reversible, 'non-destructive' manner in case something unforeseen occurs and I need to switch back.

I need to know what issues will arise adding Catalina as a dual boot on the MBP-2015 (vs. duel boot). I already have a new, unencrypted APFS volume in the same container as the Mojave volume.

How to handle Users? :

Can the Catalina User be the same current Mojave User?
Can the existing Mojave User run items on the Catalina volume?
Is there a useful way to use aliases on both OSes that would simplify reversing course, if need be?

iCloud account setup? :

With regard to accessing and using iCloud+ from both OSes, are there any special considerations?
How should Catalina iCloud be set up vs. at present on Mojave? [Are iCloud accounts unique by machine, by OS, or by User?]
In order to access the same iCloud data I do now from either the MBP-2015 Mojave or the MBP-2010:
1. Must they Catalina have the same Apple ID?
2. could they (Mojave/Catalina) be different?
3. or must they be different?

Dropbox:

Is there any special setup or limitation to use the same Dropbox account when booted in Catalina, same as if I user either Mohave or High Sierra users?

Thanks for any advice!!

MacBook Pro Retina

Posted on Mar 18, 2022 12:21 PM

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Answer 1

HWTech

Level 9

69,380 points

Mar 20, 2022 12:21 PM in response to FibreMan_85_125

First you really should not install another OS to the same Container as things will get really confusing. In fact I don't recommend dual booting to the same internal drive as that almost always ends up with two broken operating systems since users almost always select the wrong partition (aka Container) sizes or the inevitably want to remove one of the operating systems. Instead I recommend installing one of the operating systems to an external USB3 drive.

You cannot share macOS User accounts between two operating systems simultaneously. You can store files in a shared location or you can use iCloud or any other cloud file syncing service so that your files are available on any system which is able to access that cloud service. Just keep in mind that cloud syncing services are not a backup and if you delete a file from one system, then that file will also be deleted from all the other systems which are using that cloud file syncing service.

iCloud accounts follow the Apple ID. macOS does not like having multiple AppleID's associated with a single macOS user account. Yes, it is technically possible to use two different AppleID's with one macOS user account, but you will not have the full functionality available and you will run into issues doing so. I don't recommend using multiple AppleIDs with a single macOS user account. Each macOS user account should only have one AppleID associated with it for best results.

I cannot answer any of the specific questions as I don't use any of the cloud file syncing services myself.

You should always have frequent and regular backups of your computer (all volumes & operating systems if dual booting) and any external media (including items stored in the cloud) which contains important & unique data. If you are using multiple operating systems, then you will also want to have a backup of the data stored in an OS independent manner since many types of backups may only allow access to the data from the same OS (or newer) which created the backup originally.

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Catalina dual boot with (now) Mojave — Users, iCloud etc, to simplify reversing course?

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