2020 iMac i7 Can't Boot SSDs Created on 2017 iMac i5

The 2020 iMac has a T2 Security chip.

see > Change your Mac startup disk - Apple Support

What is the Security Utility.

see > What is the Startup Security Utility on Mac? - Apple Support

To change the Security settings.

see > Use macOS Recovery on an Intel-based Mac - Apple Support

For macOS, try installing macOS on the external drive using the 2020 iMac. As long as the OS is compatible with your older 2017 Mac, then it should boot just fine.

FYI, Linux is not well supported on the T2 Macs. I've never tried Linux on a T2 Desktop Mac, but half the stuff on a T2 laptop doesn't work or works poorly. Even the T1 Macs (MBPro 2016 - 2017 at any rate) don't really work well with Linux either. Linux is fine on the non-USB-C Macs such as your 2017 iMac.

Here are some sites that have some details of the Linux support for the USB-C Intel Macs (I'm not sure if they are up to date as I have had these links for a while):

https://github.com/Dunedan/mbp-2016-linux

https://t2linux.org

https://github.com/t2linux/T2-Ubuntu

https://github.com/t2linux

Surprisingly Linux on the M-series Macs is much better supported than the 2016-2020 Intel Macs, but it is still a work in progress. The official Asahi Linux distribution is Fedora Asahi Remix, but there is also an Ubuntu Asahi distribution that is working as well. There is still some rough edges & limitations at least for now.

gronesy wrote:

Hi HWTech,

Thanks for these resources. I tried the t2 process and followed it word for word. The t2 installer booted up and ran a LOT smoother than the stock Fedora Workstation 41 iso. When all was said and done, however, the new install boot up did the same nonsense the original did (showing two lines of BOOT exit code and halting, doing nothing at all, getting through the kernel selection and just spinning on the Fedora load screen) and I promise you I gave it a LOT of time before I just shut down the machine. I'm a linux vet and I know the first boot following an install usually takes a bit longer while the system is figuring out where it's been installed-LOL.

The second attempt at it after completely erasing the drive, the bootloader install failed and killed the program.

I usually don't bother with Linux on the T2 systems unless I'm just experimenting or curious.

I went through the M-series thing a year or so ago and ended up returning the machine because it just wouldn't work, the ARM linux spins were unbelievable unstable and support was a real issue.

Maybe they've come a long way since then. I hope so.

Yes, they've come a long way. It was only sometime in 2024 that the Asahi team decided to use the Fedora distribution as their OS of choice to actually run the full OS with day to day apps. Before that, the Asahi team just had their basic Asahi Linux installer which they used only for testing purposes...it was never intended to be used as a full OS. Keep in mind whenever Apple releases a new system, that it takes a bit of time for the Asahi developers to reverse engineer any changes & update the Linux kernel code (Apple doesn't help with any documentation). I haven't followed their progress closely so I'm not sure which M-series systems are well supported & which ones are still in flux.

They are still working on many areas, but I've seen reports where people can actually play games on their M-series Macs using Linux with performance being really good for those games. I only did basic stuff with the two laptops I installed Linux on because I was hoping to leverage Linux to do something for me that I found out was not going to be easy & indeed may not be possible (the impossible part has nothing to do with Linux, but the Apple hardware itself).

The other problem with the M-series machines was I'm a Windows gamer and either Parallels or the ARM version of Windows 11 couldn't handle anti-cheat software. Again, don't know if that's been fixed but I suspect not.

That is always going to be a problem unless you are running a supported OS on bare metal. Linux has had this issue for years & it is frustrating.

FYI, there are actually two types/versions of the EAC (is that correct?) anti-cheat DRM. One should be perfectly able to handle a VM or Linux (perhaps with the developer doing things a certain way), while the other one is more strict and cannot easily be made to work outside of Windows (or macOS if it is a native app). I think most of the online games tend to use the stricter DRM while single player games may utilize the less strict version. I don't recall specifics, but I think I read about it most likely on https://www.gamingonlinux.com/ a few years ago.

Sorry for the TMI reply but I did want to make sure to thank you again for all the excellent resources you gave me. That's what makes these communities thrive!

I'm glad to share. A lot of stuff I learn comes from piecing small tidbits together from various posts & even experimentation & observations.

gronesy wrote:

After my experience with multiple computers and "drive trays (remember them?) I wanted to have ONE computer that could do whatever I needed. The early Mac linux before Intel chips were quite bare to say the least. Once I got into the Intel chips, things got a lot easier.

PPC Macs were not well supported by Linux back in the day. Usually you had to go with a non-standard PPC only distro. However, some years ago I did install Debian 8 Jessie installed just fine & was quite nice, but unfortunately it was either not officially supported and/or it just didn't have a lot of the common apps available in the repository.

About the only issues I've had with Linux on Intel Macs is the Apple firmware not always recognizing the .efi bootloaders with custom names, many times I've had to rename them to the generic "boot.efi" to satisfy the unintelligent standard pushed out by MS and followed by Apple. That and the odd mix of 64bit CPUs with only 32bit firmware.

Do you think I should just try another distro from the t2 site?

The problem is with the lack of Linux drivers which is part of the Kernel which is usually similar between distributions. The problem is no one has taken the time to reverse engineer the T2 Mac hardware to make the drivers.

Do the M series linux choices require that the entire drive is used for it? Without bootcamp, are they even able to dual boot and with external SSDs?

No. Actually at the moment macOS must be installed. The current Asahi installers are just shell scripts run from within macOS. They have had to leverage the M-series boot loaders to get started and I believe they have created shims to leverage most of the standard Linux boot process. Also, Linux must be installed to the internal drive on another partition. I believe you must have about 80GB of Free storage space (I forget the exact amount since it was different between the two installs (Ubuntu & Fedora).

The Asahi blog contains some very interesting information on their methods & findings during their development.

https://asahilinux.org/blog/

I was really sad because I LOVE Fedora (ease of use and gaming) and before I bought the 2020 I just didn't do enough linux-specific research or I probably wouldn't have bought it. I just didn't realize the T2 chip was THAT big a deal. I thought it was something you could use or turn off. End of story.

The T2 security chip is the center of these 2018-2020 Intel Macs and plays a part in most functions. With my personal experience while supporting my organization's Macs, I have seen the T2 implementation is not fully thought out or implemented. I also find those systems to be more prone to Logic Board failures. I have also encountered some bugs with T2 authentication as well that result in needing to completely reset the system with a DFU firmware Restore wiping out all data on the internal SSD. Personally I would not spend any money on any 2016-2020 Intel USB-C Macs, but especially not the T2 models which tend to have a higher number of Logic Board failures than any previous models (desktops & laptops). Plus troubleshooting a T2 Mac (especially for hardware issues) is very difficult.

gronesy wrote:

HWTech,

You've just made up my mind for me! You are the EXACT person I needed to be in contact with at this time! Bar none!

Thank you for your open, honest and frank responses to my questions. As I said earlier, I had NO idea the T2 was as big an issue as it is. I've been a Mac person for almost 30 years and I've NEVER had one single machine fail on me. When you throw the logic board issues into the mix, this machine IS going back ASAP.

I'm only aware because I have to support them for my organization (they've been a nightmare, almost makes me want to support Windows' PCs). Lots of hard & frustrating lessons with very little reward unlike supporting the older Macs. While Apple has occasionally had some issues & questionable decisions in the past, these Intel USB-C Macs are a dark stain on Apple's reputation.

I think you were already mostly there anyway and you only had a small glimpse of the T2 go on.

Sorry, I don’t do or have any Linux experience.