Useful macOS defaults: Launch Services

com.apple.LaunchServices controls how macOS handles opening files and apps, including the quarantine system that warns you about downloaded files.

Turn off the "Are you sure you want to open this?" warning

When you open an app downloaded from the internet for the first time, macOS shows a warning dialog. If you find this annoying and understand the risk:

defaults write com.apple.LaunchServices LSQuarantine -bool false

This stops the quarantine warning for all future downloads. It does not turn off Gatekeeper itself. macOS still checks code signatures and notarisation. It only skips the dialog asking you to confirm.

To turn the warning back on:

defaults delete com.apple.LaunchServices LSQuarantine

What is quarantine?

When you download a file through Safari, Chrome, Mail, or most other apps, macOS marks it with a quarantine flag. This flag tells the system "this file came from the internet". The next time you open it, macOS checks the flag and shows the warning.

You can see the quarantine flag on a file:

xattr -l ~/Downloads/SomeApp.zip

Look for com.apple.quarantine in the output.

You can remove the quarantine flag from a specific file:

xattr -d com.apple.quarantine ~/Downloads/SomeApp.zip

Reset the "Open With" menu

If the "Open With" right-click menu shows duplicate entries or old apps:

/System/Library/Frameworks/CoreServices.framework/Frameworks/LaunchServices.framework/Support/lsregister -kill -r -domain local -domain system -domain user

This rebuilds the Launch Services database. It takes a moment and Finder may pause briefly while it runs.

Notes

Turning off quarantine warnings reduces your protection against malware. Only do this if you trust the sources you download from and understand the trade-off.

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