Is it possible that one installs homebrew entirely along with all casks to external SSD ? If so, how ?

[bdutta]

Output of brew config

zsh: command not found: brew

Output of brew doctor

zsh: command not found: brew

Description of issue

Relatively new to MacOS but pretty familiar with Linux, so know my way around shell and terminal. I do know how to install homebrew at it's default location. However, I have a 256GB SSD which is quite close to getting full, which I am trying to declutter but would really prefer to install homebrew itself and all of the casks on my external SSD named /Volume/ExSSD in my case. I tried to check with gemini AI, and as per it, I should run:

HOMEBREW_PREFIX=/Volumes/ExSSD/homebrew /bin/bash -c "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/HEAD/install.sh)"

However after prompting me for sudo password, I see that installer is trying to install homebrew in /opt/homebrew, so not quite what I had hoped for. Any way around this, that doesn't require a PhD in MacOS internals ?

[gromgit]

You can untar a Homebrew base tarball anywhere, but that instantly drops you to a Tier 2 support level, which may or may not matter to you.

Any formulae you install with this relocated Homebrew will automatically go to the same location (though some may have to be rebuilt from source), but most casks are just upstream installers, which have very specific ideas about where their stuff should go, so the general answer there is "no". You might successfully move /Applications-rooted casks to your external drive, or it might fail miserably, but any cask upgrades will be put right back in their original locations.

[bdutta]

Thank you for the suggestion. Given that I'm pretty new to MacOS, the tier-2 support does sound like a riskier approach, but still good to know that such an option could be explored.

[carlocab]

If your external drive is APFS, something like this might work:

sudo mount_apfs -o nobrowse /dev/diskXsY /opt/

where you'll need to adjust /dev/diskXsY to the APFS volume of your external drive.

If that worked, then you should be able to run the install script as-is.

Note: this will mount your external drive onto /opt, so it will look like Homebrew is being installed to /opt/homebrew, but /opt now actually should point to your external drive (if done correctly and I'm not mistaken about something above)

I haven't actually done this personally, so it may or may not work. But it sounds like it should do what you want.

[bdutta]

Thank you. This is a pretty interesting option. My external disk is a 1TB one, but currently partitioned (or rather not) as a single large volume (indeed APFS formatted). Is there a way to non-destructively repartition safely, to create a new partition ? Or can a folder (instead of a partition) be somehow used ? For example, could this work ?
sudo ln -s /Volumes/ExSSD/ex_opt /opt