macOS tips: defaults, chflags and directory cleanup

Compiling here some loose notes I have on macOS — adjustments I make every time I set up a new machine or need to apply again after an update.

Cleaning up directory junk

When you download a zip or receive a shared folder, it usually comes with a bunch of auxiliary files that you don’t want — Finder’s .DS_Store, Windows’ Thumbs.db, camera thumbnails and indexes, etc. To clean everything up at once:

find . -name '.DS_Store' -type f -delete
find . -name 'Thumbs.db' -type f -delete
find . -name "*.THM" -type f -delete
find . -name "*.ini" -type f -delete
find . -name "*.LRV" -type f -delete
find . -name "*.db" -type f -delete
find . -name "*.nomedia" -type f -delete

After that, take the opportunity to remove empty directories — first list to verify, then delete:

# List
find . -type d -empty
# Delete
find . -type d -empty -delete

And a trick I always use to understand what’s inside a folder before touching it: list all distinct file extensions present:

find . -type f -name '*.*' | sed 's|.*\.||' | sort -u

Useful for deciding what to clean up or what to process in bulk.

System adjustments with defaults write

defaults is the command-line utility that reads and writes macOS preferences. Most of the settings you’d find buried in Preferences (or that don’t even show up in the UI) are accessible here.

Cmd+Tab on all monitors

By default, the Cmd+Tab app switcher only appears on the primary monitor. If you use multiple displays, this is annoying — you’re focused on the secondary monitor, press Cmd+Tab and the switcher appears on the other side of the desk. To make it appear on the monitor where the cursor is:

defaults write com.apple.Dock appswitcher-all-displays -bool true
killall Dock

killall Dock restarts the Dock so the setting takes effect.

Disable smart quotes and smart dashes

macOS automatically replaces " with " " and -- with — while you type. This is great for writing in Portuguese in Pages, and terrible for writing code or markdown anywhere else. To disable globally:

defaults write NSGlobalDomain NSAutomaticQuoteSubstitutionEnabled -bool false
defaults write NSGlobalDomain NSAutomaticDashSubstitutionEnabled -bool false
defaults write com.apple.TextEdit SmartQuotes -bool false
defaults write com.apple.TextEdit SmartDashes -bool false

NSGlobalDomain affects the default behavior of all apps — but some apps ignore this global and keep their own setting. To force it across all apps registered in the system, you can sweep through them:

for d in $(defaults domains | tr -d ,); do
  osascript -e "app id \"$d\"" &>/dev/null || continue
  defaults write $d SmartQuotes -bool false
  # defaults write $d SmartDashes -bool false
  # defaults write $d SmartLinks -bool false
  # defaults write $d SmartCopyPaste -bool false
  # defaults write $d TextReplacement -bool false
  # defaults write $d CheckSpellingWhileTyping -bool false
done

osascript -e "app id \"$d\"" filters only domains that correspond to real apps — without this, you’d be writing configuration to system domains that have no associated app. I left the other lines commented because I only disable smart quotes myself; but you can enable them as needed.

Locking /etc/hosts with chflags

Several malware programs and even some software installers have the habit of modifying /etc/hosts. If you want to lock the file so that even sudo can’t edit it without unlocking first:

sudo chflags uchg /etc/hosts && sudo chflags schg /etc/hosts

• uchg → user immutable flag (any user is prevented from modifying it)
• schg → system immutable flag (not even root can modify it without unlocking; only removable in single-user mode)

To unlock when you need to edit:

sudo chflags nouchg /etc/hosts && sudo chflags noschg /etc/hosts

Works for any file, not just hosts. It’s an extra layer of protection against accidental or malicious modification.

Disabling Music.app from opening on its own

This was the one that annoyed me most: pressing play on the headset and Music.app would open out of nowhere, even if I was listening to Spotify or YouTube. I tried various approaches via defaults, launchctl, Automator scripts — nothing worked reliably in recent versions of macOS. Apple has blocked every vector that existed.

The solution that worked for me was installing BetterTouchTool and mapping the media keys to a no-op (or to the app I actually want to control). It’s not a native solution, but it’s the only one that survived system updates.

Noting this here more as a reminder: it’s not worth spending time searching for the magic defaults write that disables this. It no longer exists. Use an external tool.