Switch from Rosetta2 to native ARM install

[josherrickson]

I have an M1 Mac that I installed brew through Rosetta2. I'd like to try switching to the ARM native version. Is there a best practices approach? Do I need to completely remove everything I installed with it and reinstall? Can I have both versions installed and gradually transition?

[richiksc]

Yes, assuming your Rosetta 2 installation was installed to /usr/local as recommended, if you run the install script now, it'll install the ARM native installation to /opt/homebrew. This was part of the reason why two different prefixes were chosen.

Then, make sure /opt/homebrew/bin is added to your PATH prepended before /usr/local/bin. For example, in your .zprofile or .zshrc:

eval $(/opt/homebrew/bin/brew shellenv)

Then you can alias /usr/local/bin/brew to ibrew or x64brew or something similar:

alias ibrew='arch -x86_64 /usr/local/bin/brew`

Running brew from your terminal should run the ARM version of brew by default. You can verify by using brew config.
Running ibrew should run the Rosetta version.

Running a formula will prefer the ARM native version since /opt/homebrew/bin comes first in your path. To run the Rosetta version of a formula that you've also installed for ARM, you'd need to prefix it with /usr/local/bin. If you don't have both versions, your shell should select which one automatically. When you've completely transitioned over, if you run uninstall.sh under Rosetta, it should uninstall the Intel version of Homebrew only.

arch -x86_64 /bin/bash -c "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/master/uninstall.sh)"

[josherrickson]

Ran into a bit of trouble since I had fish (installed through x86 brew) as my default shell. (uname -m was returning x86_64.) Solution was to change the default shell to /bin/bash before installing. After that, everything worked great, thanks!

[richiksc]

Yes, you need to install ARM homebrew in an ARM shell. I highly recommend you use an ARM shell as your default shell, and just drop into an x86_64 shell if you need to do extended work with Rosetta, or just single prefix commands with arch -x86_64. fish is available as an ARM native build on ARM Homebrew as well.

And if you want to drop into a Rosetta shell, it's simple as runningarch -x86_64 /usr/local/bin/fish. You could set up an alias called x64shell or rosetta.

Most formulae are available for ARM now so you shouldn't need to use Rosetta much, the transition should be fairly easy. I've never even installed Rosetta Homebrew.

[brokosz]

What's the best way to cleanup the installed packages? My thought was to brew bundle dump then uninstall everything?, re-run the brew install natively, and reapply the bundle. Not sure if there's a recommended set of steps here or better way to do this.

[carlocab]

That sounds pretty much like how I would do it.

[sumater]

But what if I forget to bundle dump before uninstalling? that's what I did.

[gromgit]

Answered here: https://github.com/orgs/Homebrew/discussions/417#discussioncomment-10856194

[brokosz]

Okay - that worked great. Here are the steps I followed.

Migrating to native (ARM) Homebrew

These steps will remove all formulas and taps, preserving installed casks and Mac App Store apps. If you installed a new shell via Homebrew, you will have to change your shell in Terminal/iTerm before step 4 to a natively installed shell.

1. Run brew bundle dump
2. Edit brewfile to split it into two new files: remove casks and MAS apps (if mas installed), leaving all installed formulas and related taps in a reinstall file. Then save the casks and MAS apps in a cleanup file.
3. Run brew bundle cleanup -f --file <path to edited CLEANUP brewfile>
4. Run Homebrew uninstaller /bin/bash -c "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/HEAD/uninstall.sh)"
5. Reinstall homebrew using the usual command /bin/bash -c "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/HEAD/install.sh)"
6. Update your PATH to add the new Homebrew path entries
7. Run brew bundle --file <path to edited REINSTALL brewfile> to reinstall formulas and taps
8. Update profile, scripts, etc. as needed

[brokosz]

... and I missed a step in here for repointing the installed casks so now I'm off reinstalling all of those ☹️