Starting in Safe Mode clears some caches. Here is how much space that really frees
Safe Mode deletes certain system caches as it starts, which is why people suggest it for a full disk. What it clears, how to measure the difference, and limits.
Search for a full Mac and someone will suggest starting in Safe Mode. It is true that Safe Mode clears some caches on the way in. It is rarely much space, but it is safe, and it is worth knowing how to measure what it did.
What Safe Mode does
- Checks the startup disk, similar to First Aid.
- Loads only essential system software, and no login items.
- Deletes some system caches, including font caches and some kernel and system caches that are rebuilt afterwards.
It does not delete your files, photos, app data, iPhone backups or anything in your home folder.
How to start in Safe Mode
| Mac | How |
|---|---|
| Apple silicon | Shut down. Hold the power button until startup options appear. Select your disk, hold Shift, click Continue in Safe Mode |
| Intel | Restart and hold Shift until the login window appears |
You will see Safe Boot in the menu bar. Then restart normally to leave it.
Measure the difference
# Before: note the Avail number
df -h /System/Volumes/Data
# Start in Safe Mode, log in, restart normally, then run it again
df -h /System/Volumes/DataTypical gains are small, from a few hundred MB to a couple of GB. If the Mac was so full it was failing, even that can be enough to get it working again, which is the real use.
When the disk is completely full
A Mac with zero free space may not start properly. Safe Mode sometimes gets it far enough to delete something large. Mac will not boot with a full disk covers the next steps if it does not.
Common questions
Does Safe Mode free up space on a Mac?
A little. It clears some system caches while starting, usually a few hundred MB to a couple of GB. It does not delete your files.
Will Safe Mode delete my files?
No. It only clears caches that macOS rebuilds, and loads less software while running. Your files, photos and apps are untouched.
How do I start an Apple silicon Mac in Safe Mode?
Shut down, hold the power button until startup options appear, select your disk, then hold Shift and click Continue in Safe Mode.