Recently I needed to install graphviz. On their official site, they say one way is to use Homebrew.

Workaround: use Rosetta 2

Here's what I got:

% brew install graphviz 
Error: Cannot install in Homebrew on ARM processor in Intel default prefix (/usr/local)!
Please create a new installation in /opt/homebrew using one of the
"Alternative Installs" from:
  https://docs.brew.sh/Installation
You can migrate your previously installed formula list with:
  brew bundle dump

On the Homebrew website, I found this announcement.

We currently recommend running Homebrew using Intel emulation with Rosetta 2.

So back then the recommended way to install graphviz would have been to run:

% arch -x86_64 brew install graphviz
Updating Homebrew...
==> Auto-updated Homebrew!
Updated 2 taps (homebrew/core and homebrew/cask).
==> Updated Formulae
Updated 34 formulae.
==> Updated Casks
Updated 7 casks.
...

And indeed it ran fine.

Proper way: reinstall Homebrew

However on https://brew.sh/ and https://docs.brew.sh/Installation, they say their installation script now supports installing Homebrew to an Apple Silicon preferred folder. My guess is I had installed the Intel specific version of Homebrew with Rosetta 2 at a time when the new script wasn't available yet.

So if I were thorough, I should uninstall the old Intel-specific Homebrew, and reinstall the Apple Silicon specific version. Uninstalling Homebrew is done by running an uninstall script. https://github.com/homebrew/install#uninstall-homebrew. Let's try it.

% /bin/bash -c "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/HEAD/uninstall.sh)"
Warning: This script will remove:
/Users/anhtuan/Library/Caches/Homebrew/
/Users/anhtuan/Library/Logs/Homebrew/
/usr/local/Caskroom/
/usr/local/Cellar/
/usr/local/bin/brew -> /usr/local/bin/brew
Are you sure you want to uninstall Homebrew? This will remove your installed packages! [y/N] y
==> Removing Homebrew installation...
Warning: Failed to delete /usr/local/Caskroom
rm: /usr/local/Caskroom: Permission denied
Warning: Failed to delete /usr/local/Cellar
rm: /usr/local/Cellar: Permission denied
==> Removing empty directories...
Password:
==> /usr/bin/sudo /usr/bin/find /usr/local/bin /usr/local/etc /usr/local/include /usr/local/lib /usr/local/opt /usr/local/sbin /usr/local/share /usr/local/var /usr/local/Caskroom /usr/local/Cellar /usr/local/Homebrew /usr/local/Frameworks -name .DS_Store -delete
==> /usr/bin/sudo /usr/bin/find /usr/local/bin /usr/local/etc /usr/local/include /usr/local/lib /usr/local/opt /usr/local/sbin /usr/local/share /usr/local/var /usr/local/Caskroom /usr/local/Cellar /usr/local/Homebrew /usr/local/Frameworks -depth -type d -empty -exec rmdir {} ;
==> /usr/bin/sudo rmdir /usr/local
rmdir: /usr/local: Operation not permitted
Warning: Failed during: /usr/bin/sudo rmdir /usr/local
Warning: Homebrew partially uninstalled (but there were steps that failed)!
To finish uninstalling rerun this script with `sudo`.
The following possible Homebrew files were not deleted:
/usr/local/Frameworks/
/usr/local/Homebrew/
/usr/local/bin/
/usr/local/etc/
/usr/local/include/
/usr/local/lib/
/usr/local/opt/
/usr/local/sbin/
/usr/local/share/
/usr/local/var/
You may wish to remove them yourself.

Then reinstall:

% /bin/bash -c "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/HEAD/install.sh)" 
==> Checking for `sudo` access (which may request your password).
==> This script will install:
/opt/homebrew/bin/brew
/opt/homebrew/share/doc/homebrew
/opt/homebrew/share/man/man1/brew.1
/opt/homebrew/share/zsh/site-functions/_brew
/opt/homebrew/etc/bash_completion.d/brew
/opt/homebrew
==> The following new directories will be created:
/opt/homebrew/bin
/opt/homebrew/etc
/opt/homebrew/include
/opt/homebrew/lib
/opt/homebrew/sbin
/opt/homebrew/share
/opt/homebrew/var
/opt/homebrew/opt
/opt/homebrew/share/zsh
/opt/homebrew/share/zsh/site-functions
/opt/homebrew/var/homebrew
/opt/homebrew/var/homebrew/linked
/opt/homebrew/Cellar
/opt/homebrew/Caskroom
/opt/homebrew/Frameworks
==> The Xcode Command Line Tools will be installed.

Press RETURN to continue or any other key to abort
==> /usr/bin/sudo /bin/mkdir -p /opt/homebrew
==> /usr/bin/sudo /usr/sbin/chown root:wheel /opt/homebrew
==> /usr/bin/sudo /bin/mkdir -p /opt/homebrew/bin /opt/homebrew/etc /opt/homebrew/include /opt/homebrew/lib /opt/homebrew/sbin /opt/homebrew/share /opt/homebrew/var /opt/homebrew/opt /opt/homebrew/share/zsh /opt/homebrew/share/zsh/site-functions /opt/homebrew/var/homebrew /opt/homebrew/var/homebrew/linked /opt/homebrew/Cellar /opt/homebrew/Caskroom /opt/homebrew/Frameworks
==> /usr/bin/sudo /bin/chmod g+rwx /opt/homebrew/bin /opt/homebrew/etc /opt/homebrew/include /opt/homebrew/lib /opt/homebrew/sbin /opt/homebrew/share /opt/homebrew/var /opt/homebrew/opt /opt/homebrew/share/zsh /opt/homebrew/share/zsh/site-functions /opt/homebrew/var/homebrew /opt/homebrew/var/homebrew/linked /opt/homebrew/Cellar /opt/homebrew/Caskroom /opt/homebrew/Frameworks
==> /usr/bin/sudo /usr/sbin/chown anhtuan /opt/homebrew/bin /opt/homebrew/etc /opt/homebrew/include /opt/homebrew/lib /opt/homebrew/sbin /opt/homebrew/share /opt/homebrew/var /opt/homebrew/opt /opt/homebrew/share/zsh /opt/homebrew/share/zsh/site-functions /opt/homebrew/var/homebrew /opt/homebrew/var/homebrew/linked /opt/homebrew/Cellar /opt/homebrew/Caskroom /opt/homebrew/Frameworks
==> /usr/bin/sudo /usr/bin/chgrp admin /opt/homebrew/bin /opt/homebrew/etc /opt/homebrew/include /opt/homebrew/lib /opt/homebrew/sbin /opt/homebrew/share /opt/homebrew/var /opt/homebrew/opt /opt/homebrew/share/zsh /opt/homebrew/share/zsh/site-functions /opt/homebrew/var/homebrew /opt/homebrew/var/homebrew/linked /opt/homebrew/Cellar /opt/homebrew/Caskroom /opt/homebrew/Frameworks
==> /usr/bin/sudo /usr/sbin/chown -R anhtuan:admin /opt/homebrew
==> /usr/bin/sudo /bin/mkdir -p /Users/anhtuan/Library/Caches/Homebrew
==> /usr/bin/sudo /bin/chmod g+rwx /Users/anhtuan/Library/Caches/Homebrew
==> /usr/bin/sudo /usr/sbin/chown -R anhtuan /Users/anhtuan/Library/Caches/Homebrew
==> Searching online for the Command Line Tools
==> /usr/bin/sudo /usr/bin/touch /tmp/.com.apple.dt.CommandLineTools.installondemand.in-progress
==> Installing Command Line Tools for Xcode-12.5
==> /usr/bin/sudo /usr/sbin/softwareupdate -i Command\ Line\ Tools\ for\ Xcode-12.5
Software Update Tool

Finding available software

Downloading Command Line Tools for Xcode
Downloaded Command Line Tools for Xcode
Installing Command Line Tools for Xcode
Done with Command Line Tools for Xcode
Done.
==> /usr/bin/sudo /bin/rm -f /tmp/.com.apple.dt.CommandLineTools.installondemand.in-progress
==> /usr/bin/sudo /usr/bin/xcode-select --switch /Library/Developer/CommandLineTools
==> Downloading and installing Homebrew...
remote: Enumerating objects: 185181, done.
remote: Counting objects: 100% (352/352), done.
remote: Compressing objects: 100% (228/228), done.
remote: Total 185181 (delta 152), reused 292 (delta 109), pack-reused 184829
Receiving objects: 100% (185181/185181), 49.54 MiB | 9.19 MiB/s, done.
Resolving deltas: 100% (137348/137348), done.
From https://github.com/Homebrew/brew
...
HEAD is now at b7623bc97d dolt: update 0.26.8 bottle.
Warning: /opt/homebrew/bin is not in your PATH.
==> Installation successful!

==> Homebrew has enabled anonymous aggregate formulae and cask analytics.
Read the analytics documentation (and how to opt-out) here:
  https://docs.brew.sh/Analytics
No analytics data has been sent yet (or will be during this `install` run).

==> Homebrew is run entirely by unpaid volunteers. Please consider donating:
  https://github.com/Homebrew/brew#donations

==> Next steps:
- Add Homebrew to your PATH in /Users/anhtuan/.zprofile:
    echo 'eval "$(/opt/homebrew/bin/brew shellenv)"' >> /Users/anhtuan/.zprofile
    eval "$(/opt/homebrew/bin/brew shellenv)"
- Run `brew help` to get started
- Further documentation: 
    https://docs.brew.sh

At the end they ask me to add Homebrew to my PATH. If I don't add the eval "$(...)" line into .zprofile, and try to run brew, I get this:

% brew
zsh: command not found: brew

Running echo 'eval "$(/opt/homebrew/bin/brew shellenv)"' >> /Users/anhtuan/.zprofile adds the line into .zprofile, and after loading a new Terminal window, it works fine:

% brew
Example usage:
  brew search TEXT|/REGEX/
  brew info [FORMULA|CASK...]
  brew install FORMULA|CASK...
  brew update
  brew upgrade [FORMULA|CASK...]
  brew uninstall FORMULA|CASK...
  brew list [FORMULA|CASK...]

Troubleshooting:
  brew config
  brew doctor
  brew install --verbose --debug FORMULA|CASK

Contributing:
  brew create URL [--no-fetch]
  brew edit [FORMULA|CASK...]

Further help:
  brew commands
  brew help [COMMAND]
  man brew
  https://docs.brew.sh

And finally I was able to install graphviz without using Rosetta 2:

% brew install graphviz 
==> Downloading https://ghcr.io/v2/homebrew/core/libpng/manifests/1.6.37
...
==> Installing graphviz dependency: libtool
==> Pouring libtool--2.4.6_3.arm64_big_sur.bottle.tar.gz
🍺  /opt/homebrew/Cellar/libtool/2.4.6_3: 71 files, 3.7MB
==> Installing graphviz
==> Pouring graphviz--2.47.2.arm64_big_sur.bottle.tar.gz
🍺  /opt/homebrew/Cellar/graphviz/2.47.2: 301 files, 8.9MB