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Trying to go back to Mojave from Catalina. Finally got the download, but when I try to run it it says install application is too old to be opened on this version of macOS. Tried deleting it and downloading a new one, but same problem. I am not even going to put it in the same volume, but in a separate apfs volume on the same disk. Any way to get around this problem. I tried running it in safe mode, but no luck.
iMac 21.5″, macOS 10.15
Hey there! I believe if you are trying to run Mojave from Catalina, without erasing the drive, (Even to another partition), you may need to create and use a bootable installer with Mojave and boot from that, (Startup holding Option to choose the installer, then choose the other partition to install it on).
Create a bootable installer:
https://support.apple.com/en-us/HT201372
They both use APFS so that should be fine. Unless your Mac came stock with Catalina, if that was the case you wouldn’t be able to install any earlier OS, (Except on an external drive of course).
Hey there! I believe if you are trying to run Mojave from Catalina, without erasing the drive, (Even to another partition), you may need to create and use a bootable installer with Mojave and boot from that, (Startup holding Option to choose the installer, then choose the other partition to install it on).
Create a bootable installer:
https://support.apple.com/en-us/HT201372
They both use APFS so that should be fine. Unless your Mac came stock with Catalina, if that was the case you wouldn’t be able to install any earlier OS, (Except on an external drive of course).
You cannot install an older version of macOS over a new version, you need to erase the entire mac before you can do that.
If you have downloaded the Install macOS Mojave.app (6.05GBs) then you need to make a bootable USB installer with it
using these instructions.
How to create a bootable installer for macOS – Apple Support
Now make a full back up of your mac.
When you are satisfied that you have backed up your mac and all your data is safe then you can boot to the
bootable USB installer you made earlier.
Restart your mac while pressing and holding the option/ alt key. In a couple of minutes you should see the
Startup Manager, select the bootable USB and press Return.
Again in a couple of minutes your mac will boot to the USB and you will see a Utilities panel.
Click on Disk Utility and press Continue.
Click on View in the menubar and select Show All Devices.
Now highlight the uppermost Disk (not any of the indented Volumes) in the left hand panel.
Click on Erase.
Give the Disk a name.
Format: APFS.
Scheme: GUID Partition Map.
Click Erase.
Quit Disk Utility.
Click on Install OS and press Continue.
The installation process should start follow the prompts.
When the installation has finished you can then think about restoring
you personal data from the back up you made earlier.
Only restore your personal data do not restore any System or Library files
as this may put Catalina back on your mac.
Do not restore any of the Apple apps that come with the OS as they will
be Catalina versions and won't work in Mojave, only restore third party apps
you know are compatible with Mojave.
I’ve ran both OS’ on the same disk, they just need to be partitioned before creating the installer, using APFS of course.
I’d say an ever better idea, (If you’re able to), would be get get an external drive, (You can get ones with large capacity for pretty cheap). Use the bootable installer on that drive and just plug it in when ready to use Mojave, but either way should work fine!
Thank you. I've got Mojave running in a separate volume now, after making the bootable installer, and still have Catalina in it's volume.
Awesome! Glad it worked out, I know how handy that can be!
Trying to go back to Mojave from Catalina.
