Startup disk full on Mac: what to do first

Part of: Mac storage full? Find what is using it and free up space safely (Storage full)

If your Mac says the startup disk is almost full, you can get room back in a few minutes with safe steps. Do those first, and avoid anything that deletes system files. Speed is not worth a mistake here.

First, check how bad it is

Run this in Terminal. It only reads:

df -h /System/Volumes/Data

The Avail column shows what is left. Storage settings shows the same thing as a bar: Apple menu > System Settings > General > Storage.

What to do first, in order

1. Look in the Trash, then empty it. Use Put Back for anything you want to keep. The space is freed only when the Trash is emptied. See why the Trash does not free space until you empty it.
2. Check Downloads. Sort it by size. Remove files you have already used. Clean up the Downloads folder shows how.
3. Remove old installers. Disk images (DMG files) are safe to remove once the app is installed. How to delete DMG files.
4. Find a few large files. One big file can be worth more than a thousand small ones. Find large files on a Mac.
5. Look at iPhone backups. Each can be many gigabytes, but you may need them. iPhone backups on your Mac.

Check df again after each step. Stop when you have a comfortable margin.

Safe, Risky, Never

• Safe: emptying the Trash after a look, old installers, downloads you have already used.
• Risky: old backups, large files you do not recognise, anything inside your Library folder.
• Never: deleting system folders, the contents of your Photos library, or things you cannot name.

Move files instead of deleting them

If the big files are yours and you still need them, you do not have to choose between keeping and deleting. Copy them to an external drive or another place you trust. Open a few of the copies to check that they work. Only then remove the originals. This keeps your data, and the space is released once the originals are gone. For anything you cannot replace, keep the copy until you are sure.

What not to do

Under pressure, people try quick fixes that cause trouble. Avoid these:

• Deleting folders from the system or Library because they look big. Some hold settings and data that apps need. Removing the wrong one can make an app lose its data or fail to open.
• Deleting items from the Photos library folder in Finder. Photos manages its own database, and files removed behind its back can leave it inconsistent. Manage photos inside the Photos app.
• Using Terminal commands you found but do not understand. A command that removes files cannot be undone.
• Removing something just because it is big. Check what it is first.

If it will not free up

Sometimes the number does not change after you delete things. Snapshots and purgeable space can hold some of it, and macOS releases them when it needs room. You can look at snapshots with tmutil listlocalsnapshots /. Mac storage full but no files? explains why this happens. A restart can also help macOS settle the numbers.

If you cannot even delete files because there is almost no room, free a little first by emptying the Trash, then continue.

When an update needs the room

If you are low on space because an update will not install, read not enough space to update macOS.

Make a plan before you start

When the warning appears, it is tempting to remove the first big thing you see. A short plan avoids regret. Decide how much room you need, for example enough to update and to work comfortably. Write down which folders you will look at, in the order above. Then take one step at a time and check the free space after each, so you can stop as soon as you have enough.

It also helps to know which files you could not replace. Your documents, photos and anything without a second copy deserve a backup before you start. A backup costs some time and, once done, takes the fear out of every other step. If you have no backup, make one of the files you care about first, and only then continue.

See where the space is

DiskJoy is our product. It scans the folders you choose and reports allocated bytes, a lower bound that leaves out space shared between files (for example APFS clones). A scan only reads sizes and dates and changes nothing. Its reclaimable figure is a lower-bound estimate, not an exact number. DiskJoy is pre-alpha and cleanup is not available yet, so you remove things yourself. Download DiskJoy for Mac if you want a clear picture before you decide.

After the emergency

Once you have breathing room, look at the cause. The complete guide to freeing up space on a Mac covers it in order, and Mac keeps running out of space helps if the disk fills again.