Catalina on bootable external drive

[funkyfreddy]

I have a MacBook Pro running Big Sur and wanted to install Catalina on a bootable external drive, mainly to run MOTU's Ethno and other programs I can't currently run under Big Sur. What's the easiest way to do this? Thanks, Fred

[bayswater]

I have Mojave and Big Sur on a 2018 Mini. Rather than putting BS on an external, I put it on a volume on the internal drive. A volume rather than a partition because then both systems share the space on the drive rather than partitions which require dedicated space. BS takes up an additional 10g. You can set this up in Diskutility. I also found that BS can see and run many apps that are on the Mojave volume if auth etc files can be found on the BS drive.

I’m sure there is a host of reasons not to do it this way but it has worked for me for a couple of years now.

[mikehalloran]

I have Mojave and Big Sur on a 2018 Mini. Rather than putting BS on an external, I put it on a volume on the internal drive. A volume rather than a partition because then both systems share the space on the drive rather than partitions which require dedicated space. BS takes up an additional 10g. You can set this up in Diskutility. I also found that BS can see and run many apps that are on the Mojave volume if auth etc files can be found on the BS drive.

I’m sure there is a host of reasons not to do it this way but it has worked for me for a couple of years now.

The only reason I can think of not to do this is you just don't have the space. Otherwise, use Volumes instead of Partitions on APFS formatted drives.

Since your MBP has a T2 chip, you have to defeat a security setting in the Repair Partition that prevents multiple boot volumes or booting from an external. Apple has support docs on this but I have the instructions archived somewhere if necessary.

I, too, have Mojave and Big Sur. There are a couple of 32 bit bread and butter apps that require Mojave. Works great on my 2017. As you have a 2019, Catalina should have been the bundled MacOS so I'm not sure that Mojave is an option for you unless yours was early 2019.

[funkyfreddy]

Since your MBP has a T2 chip, you have to defeat a security setting in the Repair Partition that prevents multiple boot volumes or booting from an external. Apple has support docs on this but I have the instructions archived somewhere if necessary.

Wow.... sounds way more complicated than it used to be

This explains why I can't boot into my other drives that I used to be able to do with my iMac. I'd love to get the info on how to defeat the security setting when you get a chance to find them Mike.

Thanks Bayswater and Mike for your input and info!

[mikehalloran]

These two documents should tell you what you need to know.

https://support.apple.com/guide/securit ... 34e5b5/web

https://support.apple.com/en-us/HT208198

These can only be accessed through the Repair Partition. Shut down, boot with Command r keys held down. Until the above is run, disconnect any externals with a bootable MacOS or you will never see the Repair Partition on a T2 Mac. Fun, huh? Once the security settings are changed, not only can you access bootable externals but the Repair Partition will again be available.

[funkyfreddy]

Thanks again Mike!

I'm going to start another thread in General Macintosh and pick your brains about the issue my old iMac is having.

Thanks,
Fred