How to downgrade Catalina to Mojave without Recovery Mode?

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iMac Intel 27" EMC 2429

Model A1312 / Mid 2011 / 2.7 & 3.1 GHz Core i5 or 3.4 GHz Core i7 Processor, ID iMac12,2

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pig @pigwidgeon

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发帖于: 2020年2月5日

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How to downgrade Catalina to Mojave without Recovery Mode?

iMac bricked!

Neither Recovery Mode nor Internet recovery worked. Couldn’t install High Sierra via bootable Drive. Tried a Catalina patch and it finally recovered. Now having too many issues with Catalina.

Need to test downgrading. Recovery Mode and Internet Recovery still does not work upon start up. Safe mode returns a Circle Cross out.

I have backed up the Mac via Time Machine + External with Catalina.

I now can’t figure out how to erase my HD, install Mojave from my bootable USB, without the system able to go in recovery mode.

Am I forced to use command line sequence to accomplish this?

Any help appreciated.

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Dan @danj 声誉积分: 479.3千 Self employed contract worker 35 329 971 · Answer 1 · 2020-02-05T15:14:56-07:00

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Dan @danj

声誉积分: 479.3千

Self employed contract worker

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发帖于: 2020年2月5日

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Sadly, you need to work from an external bootable drive to completely wipe the drive and then rebuild. With the current version of APFS you can’t back off! Apple is still altering the drives structure under APFS (still a work in progress!)

Now the fun part! Apple messed up the certificates in the older macOS releases Sierra, High Sierra & Mojave! You need to get the fixed files:

Here’s more on the certificate issue If you've got an old macOS install image, it will probably stop working today

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Thanks for the reply. How do I "work from an external bootable drive to completely wipe the drive and then rebuild"?

由 pig 完成的 2020年2月5日

First, create an OS installer drive, You'll want to use a USB-A Thumb drive with a USB-A to USB-C dongle (that way you only need one set of thumb drives for the different OS's you want to use and can be used on the different systems. As an example I have 6 setup now (of course using the correct OS for the given system).

Pick the OS you want to use from this list. In our case you really should stick with Sierra:

● How to create a bootable macOS Sierra installer drive

● How to create a bootable macOS High Sierra installer drive

● How to create a bootable macOS Mojave installer drive

● How to create a bootable macOS Catalina installer drive

Make sure to redo the format to GUID/HFS+ (Journaled) as the default is FAT32 on the thumb drives.

Once you've created the needed drive, connect it and then restart the system pressing the Option (⌥) key to get to the Startup Manager so you can select the thumb drive. Once started go to the menu to launch Disk Utility and then delete all of the partitions and containers. Then reformat the drive, at the end launch the OS installer.

Reference: Mac startup key combinations

由 Dan 完成的 2020年2月5日

Thanks so much Dan for taking the time to write this! So delete both my HD and Data? I've deleted just the Macintosh HD via my Bootable USB (Mojave), (my patches for Sierra and High Sierra weren't loading upon reboot + Option and initiating the drive). I tried to install the Bootable USB on the erased Macintosh HD, it runs, then reboots and I get the

由 pig 完成的 2020年2月6日

Update, even after erasing Macintosh HD - data, still can't load the Bootable OS drive after the disk utility section, where I select to install the Bootable OS on Macintosh HD

由 pig 完成的 2020年2月6日

OK time to replace the drive! What do you have presently installed?

由 Dan 完成的 2020年2月6日

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iMac Intel 27" EMC 2429

How to downgrade Catalina to Mojave without Recovery Mode?

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