Cannot erase install Big sur on Monterey Machine

[Abhinav_mohan]

Hi there ,

I am using a script to erase install Big Sur on our machines.

I was testing out the script and it works fine for all devices with Big Sur or previous version above 10.9. But it doesn't work for Laptops which are already in Monterey

Actual script which do my erase / install process

"$installer_path" --eraseinstall --agreetolicense --forcequitapps --newvolumename "$computername" &

 "$jamfHelper" -windowType hud -lockhud -heading "ERASING AND INSTALLING" -description "$erase_dialog" -icon "$mac_os_installer_path" 

If pass this command on Monterey device , it doesn't give no output. 
Any suggestions on how to make it work?

[AtillaTheC · Accepted solution]

only real way to downgrade an OS is to create an external USB bootable installer and then manually erase/install from that. 

[sdagley · Accepted solution]

@Abhinav_mohan The reply by @AtillaTheC is correct, but left out that for T2 equipped Macs you won't be able to boot from a USB Big Sur installer until you boot intoRecovery Mode and change the startup security options to allow booting from a USB drive.

I've also go to ask _why_ you would ever want to downgrade a Mac already running Monterey to Big Sur? My personal opinion is that Big Sur was the Alpha release of Monterey, and the faster I get my org's Macs to Monterey the hap[pier I'll be. My org made the decision to not make Big Sur a recommended upgrade, and only supported it for Macs delivered with it or special cases. Monterey on the other hand we've already made available as a Self Service upgrade (which handles the prerequisite security tool updates before installing Monterey).

[AtillaTheC · Accepted solution]

only real way to downgrade an OS is to create an external USB bootable installer and then manually erase/install from that. 

[sdagley · Accepted solution]

@Abhinav_mohan The reply by @AtillaTheC is correct, but left out that for T2 equipped Macs you won't be able to boot from a USB Big Sur installer until you boot intoRecovery Mode and change the startup security options to allow booting from a USB drive.

I've also go to ask _why_ you would ever want to downgrade a Mac already running Monterey to Big Sur? My personal opinion is that Big Sur was the Alpha release of Monterey, and the faster I get my org's Macs to Monterey the hap[pier I'll be. My org made the decision to not make Big Sur a recommended upgrade, and only supported it for Macs delivered with it or special cases. Monterey on the other hand we've already made available as a Self Service upgrade (which handles the prerequisite security tool updates before installing Monterey).

[Abhinav_mohan]

We have a company policy to reimage all the devices which havent checked for 3 months. We only have upgrade as big sur in place for now. So was testing if its possible to wipe and install big sur on machines which have Monterey. Just testing to check few things.

[dlondon]

One of us might downgrade to test something on Big Sur.  My test machines frequently get wiped and rebuilt with various OS Versions.

[tsylwest · Accepted solution]

One final way to downgrade an older mac with a USB stick (but need an internet connection) is to hold down Shift-Option-Command-R on boot which will install the original version of MacOS that the laptop came with, and then upgrade it to what ever version above that using this page.

Takes a crazy long amount of time, but one of the more reliable methods if all else fails.