How can I download a dmg of Big Sur in Monterey OS?

[I WAS the one]

I need to install Big Sur again on the main internal drive. I've been using Monterey on an external SSD, and it works great, but the Big Sur is behaving bad, and I think that with a clean install everything will be fine. Here's the thing... when I download Big Sur it pops a window saying I can't install the OS, but I don't want to install it on the Monterey, I want to be able to install Big Sur in the other drive. Thinking that I need to erase the drive first and all. Right? I can't afford on losing all that I have in the Monterey one. My work is there and everything.

Can I just restore Big Sur the normal way on the Big Sur drive? I don't want to lose the option to boot up from Monterey OS.

If that can't be done, Can I Install Big Sur from Monterey on the other drive?

 

[Nermal]

The easiest way is probably to use the createinstallmedia tool included 'inside' the Big Sur installer to create a USB drive, boot from it, and install from there.

 

[kitKAC]

Turn off the machine, unplug the drive that has Monterey on it and boot into Recovery. You can wipe the disk and reinstall the current version of Big Sur that you're currently running.

 

[AlixSPQR]

You can download several Big Sur version installers with the help of OCLP. They are not .dmg, though.

 

[BeatCrazy]

How to create a bootable macOS Big Sur USB installer drive - 9to5Mac

This tutorial shows you how to create a bootable macOS Big Sur USB installer drive, which can be handy for performing fresh installs on your Mac.

9to5mac.com

 

[I WAS the one]

I need to know before doing this. After re-installing Big Sur, Am I going to be able to boot from my external drive? I don’t want to mess with my work drive. I need to be able to use Monterey external drive as a bootable option. Thanks in advance.

 

[Fishrrman]

You could try the "Mist" OS download tool.

Get it here:

GitHub - ninxsoft/Mist: A Mac utility that automatically downloads macOS Firmwares / Installers.

A Mac utility that automatically downloads macOS Firmwares / Installers. - ninxsoft/Mist

github.com

Go to the right side of page, find "releases", click "latest".

This will download a small pkg file you run, and afterwards, you can use terminal to get what you need.

If you scroll down the page listed above, you can find the appropriate terminal commands to use to download full installers.

Once you have the installer...
I think you might be able to use either "DiskMaker X" or "Install Disk Creator" to create a bootable USB flash drive installer.

Not sure, you'll have to try this yourself.

 

[bogdanw]

No third-party tool needed to create a dmg, from Terminal:
1. download the Big Sur 11.6.5 installer

softwareupdate --list-full-installers

softwareupdate --fetch-full-installer --full-installer-version 11.6.5

or

open "x-apple.systempreferences:com.apple.preferences.softwareupdate?client=bau&installMajorOSVersion=11.6.5"

2. Create a dmg

hdiutil create 1016.dmg -size 16g -layout SPUD -fs HFS+J

hdiutil attach 1016.dmg -noverify -nobrowse -mountpoint /Volumes/InstallBigSur

sudo /Applications/Install\ macOS\ Big\ Sur.app/Contents/Resources/createinstallmedia --volume /Volumes/InstallBigSur

hdiutil detach /Volumes/Install\ macOS\ Big\ Sur

hdiutil resize -sectors min 1016.dmg

 

[Nermal]

I need to know before doing this. After re-installing Big Sur, Am I going to be able to boot from my external drive? I don’t want to mess with my work drive. I need to be able to use Monterey external drive as a bootable option. Thanks in advance.

Yep. The installer will ask which drive you want to install to. So long as you choose the internal drive then you'll still have the option to boot into either installation (either by holding Option at boot, or from System Preferences/Startup Disk).

It might be best to disconnect the external before installing, so that you don't install to it by mistake.

 

[posguy99]

And no one references Apple's own knowledge base page.

How to download and install macOS - Apple Support

Download and install current or previous versions of the Mac operating system on compatible Mac computers.

support.apple.com

 

[davidlv]

And no one references Apple's own knowledge base page.

How to download and install macOS - Apple Support

Download and install current or previous versions of the Mac operating system on compatible Mac computers.

support.apple.com

And no one mentioned this?

macOS Big Sur Full Installer Database. Download Directly from Apple!

You can now download Beta & Final versions of macOS Big Sur 11 my new database! Every available version of Big Sur listed for quick download!

mrmacintosh.com

 

[CoastalOR]

And no one references Apple's own knowledge base page.

How to download and install macOS - Apple Support

Download and install current or previous versions of the Mac operating system on compatible Mac computers.

support.apple.com

The Apple download links with instructions on creating a USB installer were in the Apple link in POST #2.

 

[I WAS the one]

Thanks for your help. I will share what I did and how everything ended.

1. I downloaded Carbon Copy Cloner
2. Clone my external drive with Monterey OS as a bootable clone with the legacy bootable feature. If you want to try this on another drive that is not the internal it won’t work because Apple will need to approve the drive first. So it need to be an installed and never touched ssd or drive from Apple to be approved. I was successful but I noticed the apps from third party needed manual activation so I went again and try plan B. Factory Restore from Apple.
3. Disconnected the external drive and start the Mac holding power to choose the internal drive and install the OS like factory reset.
4. Clicked to erase disk, and follow instruction. Installed Monterey on internal drive by mistake instead of Big Sur. I know…
5. connect the external drive and reboot with externa.
6. Clone my external to internal drive with CCC.
7. Boot from internal, erased the external and assign it to Time Machine.
8. Everything is working fine… in macOS Monterey. Hoping the best.



I created a bootable thumbdrive with Big Sur for emergency.