Sometimes when I run a ember serve I get this error:

EMFILE: too many open files, watch

I don't really understand why this happens, but it's usually after a restart when some esoteric settings I used previously get reset. Or after a brew update that upgrades watchman.

The docs are very spotty, but my coworker told me a workaround that's not totally random and also makes enough sense in my mental model that I will probably use it forever.

The mental model is something like: "newer versions of watchman break ember server, so use an older version". This makes sense to me. Some implicit update is causing issues, rollback.

1. brew rm watchman

   This removes watchman from your system.

2. curl https://raw.githubusercontent.com/Homebrew/homebrew-core/ec72d21865f5b18191594565fda4157b7576dea8/Formula/watchman.rb | pbcopy

   This updates the "Formula" for installing watchman with the 4.9.0 version, which is the working version¹

3. brew edit watchman

   This opens up the file where Homebrew keeps the formula for installing watchman on your system.

4. paste and save

   Save the 4.9.0 installer for watchman into the file, so that it will install 4.9.0 next time you install.

5. HOMEBREW_UPDATE_PREINSTALL=0 brew install watchman

   Installs watchman, but opts out of running updating all Homebrew formulas before doing the install (which would overwrite the formula) we just edited before. You can also add this to your shell profile to always have this behavior.

6. brew pin watchman

   Prevents upgrading the formula in the future.

Another coworker pointed me to more commands from watchman, which look like reset steps.

watchman watch-del .
watchman watch .

One of these days I'll dig deeper to understand how these tools are actually working together and if there's some root cause issue that can be solved, but there's only so many rabbit holes you can go down (and then write about)!