Dual Booting Sierra and Big Sur

[ShiniestofShinies]

Dear Mac Experts,

I have recently decided to give Big Sur a try. In order to do this I have prepared a clean install on a brand new external ssd.
The process was quite smooth, and both Sierra (internal) and Big Sur (external) are booting fine.

One issue I have run into regards permissions when accessing files on the internal from the externally booted Big Sur, and vice versa.
When using Big Sur if I wish to access my old internal documents, I don't have access.
Opening get info on my old documents for example reveals a spinning fetching icon.
I can manually set read write access to my Big Sur user, but then when I go back to Sierra I have to set it back?
I have found that setting permissions to everyone when seems to allow universal access, but are there problems with this.
Also I know I have the option to ignore ownership on the internal when booted from Big Sur but will that create problems.

Basically, I wish to have free access to Sierra documents when booted in Big Sur and vice versa, ideally without having to fiddle with permissions every single time.

Help appreciated.

Best

Kevin

 

[gilby101]

Basically, I wish to have free access to Sierra documents when booted in Big Sur and vice versa, ideally without having to fiddle with permissions every single time.

You won't like this.

I don't think that is a realistic (or safe) expectation, even if you were to sort out permissions issues.

When running Sierra: Expect to have problems accessing the BS volume as Sierra does not know about APFS as used by BS. Be very careful about changing anything on the BS volume. I am not even sure that Spotlight is compatible.

When running BS: You should be able to see and (if careful) change data (i.e. your documents) without issue. But don't touch system stuff or music and photo libraries.

Permissions issue may well be because your username has different UIDs on each system. So the 'owner' is different even if the name of the owner is the same.

Recommendations:
Make sure are confident regarding recovery of Sierra (assuming it is your main system) from backup.
To share documents, etc. I would create a special folder on the Sierra system. And easiest to make it Everyone R/W.
Avoid running apps installed on the other OS. Do a new install of each app on the BS system.
Never use Apple's photo and music apps to access libraries held by the other.
Treat this as a temporary measure until you are confident of using BS.

 

[ShiniestofShinies]

You won't like this.

I don't think that is a realistic (or safe) expectation, even if you were to sort out permissions issues.

When running Sierra: Expect to have problems accessing the BS volume as Sierra does not know about APFS as used by BS. Be very careful about changing anything on the BS volume. I am not even sure that Spotlight is compatible.

When running BS: You should be able to see and (if careful) change data (i.e. your documents) without issue. But don't touch system stuff or music and photo libraries.

Permissions issue may well be because your username has different UIDs on each system. So the 'owner' is different even if the name of the owner is the same.

Recommendations:
Make sure are confident regarding recovery of Sierra (assuming it is your main system) from backup.
To share documents, etc. I would create a special folder on the Sierra system. And easiest to make it Everyone R/W.
Avoid running apps installed on the other OS. Do a new install of each app on the BS system.
Never use Apple's photo and music apps to access libraries held by the other.
Treat this as a temporary measure until you are confident of using BS.

Thanks for the reply.

My original plan was just to migrate my main system to Big Sur on the external. However there is some software incompatibility for something I need regularly. Dual booting was plan B. Weirdly I notice since I backed up the system and installed Big Sur on the external Sierra seems faster.

If I upgrade the Sierra internal to Mojave then that might play nicer with Big Sur on the external, bypassing some of the file system issues you mention?

 

[gilby101]

If I upgrade the Sierra internal to Mojave then that might play nicer with Big Sur on the external, bypassing some of the file system issues you mention?

Not much better, I suspect.

You could approach your incompatible software in another way. Run Big Sur all the time and install virtual machine software (e.g. VMware Fusion (free for personal use) or Parallels) and create a virtual machine running an old version of macOS and your incompatible software. This works well for most (but not all) software.

 

[MacCraig Pro]

Why Sierra? That was a dog of an OS, much better to upgrade to High Sierra or Mojave if you don't want to go to Big Sur.

 

[ShiniestofShinies]

Sierra was just the OS that shipped with the system. I’m not a fan of upgrading generally since something usually breaks, and it’s time consuming. But yes Sierra was never a good experience, and the machine was slower than the mountain lion machine from 2011 it replaced. I moved the machine to Mojave today and it seems a bit better. Should have done it ages ago.

Virtualising an older OS inside Big Sur is an interesting idea that I had not thought of. Might give that a go.