Can't choose OS version (from Big Sur?)

[woodmanb]

Hi,

First time posting at GiHub! Hope you all are safe and are having a nice 2021.

I've successfully tested erase-install in the past, today I was going to write a graphical script to be user-friendly, and realized I cannot choose any version prior to Big Sur although they are available.

Current installed version is: 11.1
Aiming to reinstall version: 10.15 (tried 10.14 as well, none of them worked)

`sudo bash erase-install.sh --erase --os=10.15

[erase-install] v0.17.2 script execution started: jueves, 14 de enero de 2021, 18:07:01 CET
[erase-install] Caffeinating this script (pid=1934)
[erase-install] Looking for existing installer
[find_existing_installer] No valid installer found.
[erase-install] Starting download process
[get_installinstallmacos] installinstallmacos.py is in /Library/Management/erase-install
[run_installinstallmacos] Checking that selected OS 10.15 is available

[run_installinstallmacos] This command is now being run:

installinstallmacos.py --workdir=/Library/Management/erase-install --ignore-cache --raw --os=10.15 --validate

installinstallmacos.py - get macOS installers from the Apple software catalog

This Mac:
Model Identifier : MacBookPro16,1

Bridge ID : J152fAP
Board ID : Mac-XXXXXXX (erased for privacy)
OS Version : 11.1
Build ID : 20C69

ProductID Version Build Post Date Title

1 001-15219 10.15.5 19F2200 2020-06-15 macOS Catalina
2 001-68446 10.15.7 19H15 2020-11-11 macOS Catalina
3 001-04366 10.15.4 19E2269 2020-05-04 macOS Catalina
4 061-86291 10.15.3 19D2064 2020-03-23 macOS Catalina
5 041-91758 10.13.6 17G66 2019-10-19 macOS High Sierra
6 001-57224 10.15.7 19H4 2020-10-27 macOS Catalina
7 061-26589 10.14.6 18G103 2019-10-14 macOS Mojave
8 001-51042 10.15.7 19H2 2020-09-24 macOS Catalina
9 001-36735 10.15.6 19G2006 2020-08-06 macOS Catalina
10 001-86606 11.1 20C69 2020-12-14 macOS Big Sur
11 041-88800 10.14.4 18E2034 2019-10-23 macOS Mojave
12 041-90855 10.13.5 17F66a 2019-10-23 Install macOS High Sierra Beta
13 061-26578 10.14.5 18F2059 2019-10-14 macOS Mojave
14 001-36801 10.15.6 19G2021 2020-08-12 macOS Catalina

OS 10.15 is not available. Run again without --os argument to select a valid build to download.

[run_installinstallmacos] No disk image found. I guess nothing got downloaded.

`

It says OS 10.15 is not available although its in the list. I've tried pointing specific versions and builds. No luck at all.

Is it because I'm running 11.1? If so, is there any way of doing it using erase-install to avoid all the manual work?

Thanks a lot!

[adamzeitoun]

Bump! looking to do the same thing. Need to downgrade from Big Sur to Catalina. Help would be greatly appreciated!! Thanks

[grahampugh]

You cannot downgrade using startosinstall. You can download the installer and create an external installation drive with createosinstallmedia, then boot from that drive on the device you wish to downgrade.