Restart Your Mac to Instantly Free Up 20GB+ of Disk Space
You open System Settings, check your storage, and something feels off. “System Data” or “macOS” is eating 30–40GB, but you haven’t installed anything new. Before you start digging through folders or running Terminal commands, try the simplest fix in the book: restart your Mac.
The Problem: Downloaded Updates Sitting on Your Disk
When macOS downloads an update — especially a major point release — it pulls the full installer to your drive before applying it. These installers can be 5–15GB each. If you’ve been postponing a restart, or your Mac quietly downloaded an update in the background overnight, that installer is just sitting there consuming space.
And it doesn’t stop at one. If multiple updates have accumulated — say, you skipped a few months of restarts — you can end up with several installer files stacked on top of each other. That’s how “System Data” quietly balloons to 30GB or more without you doing anything.
The Fix: Just Restart
When you restart and the update installs, macOS automatically cleans up the installer files afterward. No manual steps, no Terminal commands, no third-party tools needed.
You might spend an hour digging through Library folders looking for space savings, when a two-minute restart would have freed 20GB. I’ve seen 20GB+ disappear after a single restart on a MacBook that hadn’t been rebooted in weeks.
How to Check If This Applies to You
Go to System Settings > General > Software Update. If there’s a pending update listed, that installer is almost certainly on your disk right now.
You can also go to Apple menu > About This Mac > Storage (or System Settings > General > Storage on newer macOS). If the “macOS” or “System Data” slice looks disproportionately large — think 20–40GB on a machine where you haven’t done anything unusual — a pending update is a likely explanation.
Quick Tip: Restart Weekly
Make it a habit to restart your Mac at least once a week. Beyond cleaning up update installers, a regular restart:
- Clears temporary files that build up in
/tmpand system cache directories - Resets memory leaks from apps that have been running for days
- Flushes kernel extension caches and other low-level system state
- Applies security patches that can’t fully take effect until a reboot
It takes two minutes and routinely buys you back gigabytes of space you didn’t know you were missing.
Want to Find Other Hidden Space Hogs?
A pending update is one culprit — but it’s rarely the only one. Old caches, forgotten downloads, Xcode build artifacts, and Time Machine snapshots can silently eat another 20–50GB on top of that.
Want to find other hidden space hogs on your Mac? Download DiskCopilot — it scans your drive and uses AI to tell you exactly what’s safe to delete.