Mac says disk is full — what to delete (and what not to)

The “Your startup disk is almost full” warning shows up at the worst times — usually when you’re trying to update macOS or render a video. Before you start panic-deleting, here’s the right list of what to clear and what to absolutely leave alone.

Safe to delete

These are reliably safe. None of them affect how macOS or your apps work — at most you’ll re-download an installer or have a slower first app launch.

1. Anything in Downloads. If it matters, you have it elsewhere. Installer DMGs especially.
2. Files in Trash. Right-click the Dock Trash icon > Empty Trash.
3. Old iOS device backups. Finder > your phone > Manage Backups.
4. Mail attachments. Mail caches every attachment in ~/Library/Containers/com.apple.mail/Data/Library/Mail Downloads/. The Mail app re-downloads from the server if needed.
5. App caches. Folders inside ~/Library/Caches/ are rebuilt on demand. Delete folders for apps you still use; they'll be slightly slower on next launch.
6. Old screen recordings and screenshots. Check your Desktop and the folder you configured for screenshots.
7. Time Machine local snapshots. If you have a Time Machine drive connected occasionally, macOS keeps "local snapshots" that count as used space. Run tmutil listlocalsnapshots / to see them; they auto-purge when space is needed, so usually you don't have to act.

Do NOT delete

These look like garbage but aren’t. Deleting them breaks things.

1. /System — read-only on modern macOS but still possible to mess with via Terminal. Don't.
2. /Library (not ~/Library) — system-wide library; contains things many apps depend on.
3. ~/Library/Application Support for apps you currently use — this is where their settings and data live.
4. ~/Library/Keychains — your passwords and certificates.
5. Anything in /private/var.
6. The hidden .DS_Store files. Annoying, harmless, regenerated automatically.

A quick command to find the worst offenders

du -sh ~/* 2>/dev/null | sort -h | tail -10

That shows the ten largest folders in your home directory. Whatever’s biggest is your target.

The hidden category: duplicates

Once you’ve cleared the obvious stuff, the next biggest bucket on most Macs is duplicate files. A single photo imported from your phone and your camera. A PDF saved to Downloads, then dragged to Documents. A project folder copied “just in case.” These look like legitimate files, so nothing flags them.

Download Dupe and run a scan — it hashes every file with SHA-256 to find byte-identical matches. Moves duplicates to the Trash (not permanent delete) and skips system files and app bundles. $14.99 once, no subscription. Most first scans recover 5–20 GB.