"Can't be modified": why a Mac will not copy, move or delete on a drive, and how to tell which kind of read only it is
When Finder says a drive or folder can't be modified, it is read only for one of four reasons. Each has a different fix, and one has no fix at all.
Finder says The item can't be moved because "Untitled" can't be modified, or the copy simply will not start. The destination is read only. There are four reasons that can be true, and the fix depends entirely on which one it is.
Find out which
Select the drive or folder and press Command I to open Get Info. Look at Format near the top and at Sharing & Permissions at the bottom.
| What you see | Why it is read only | Fix |
|---|---|---|
| Format: NTFS | macOS reads NTFS but does not write to it | Copy elsewhere, or reformat. See NTFS drives on a Mac |
| "You can only read" | Permissions on the drive or folder | Unlock the padlock, give yourself Read & Write, or tick Ignore ownership on this volume |
| The drive is Macintosh HD | The system volume is sealed and always read only | Save to your home folder instead |
| A locked SD card or write protected drive | Hardware switch | Slide the lock switch |
The system volume is meant to be read only
Since macOS Catalina, the system lives on its own sealed volume. You cannot write to /System, and copying to the top level of Macintosh HD fails by design. Your files belong in your home folder, which lives on the separate Data volume. Our guide to Macintosh HD and Macintosh HD Data explains the split.
Permissions on an external drive
A drive that came from another Mac keeps that Mac's owner on its files. The quickest way past it, for a drive only you use:
- Get Info on the drive.
- Click the padlock and enter your password.
- Tick Ignore ownership on this volume.
For a single stubborn folder, Terminal shows who owns it:
ls -le /Volumes/Untitled/
# give yourself the folder, if you are sure it is yours
sudo chown -R "$USER" /Volumes/Untitled/FolderWhen it is the drive failing
A drive that mounts read only after First Aid reports errors, or an SD card that suddenly will not accept files, may be protecting itself. Copy what you can, then check it with Disk Utility First Aid before trusting it with anything new.
Common questions
Why does my Mac say an external drive can't be modified?
The drive is read only. Usually it is formatted NTFS, which macOS only reads, or its permissions belong to another Mac. Get Info on the drive shows which.
Can I copy files to Macintosh HD?
Not to the top level. The system volume is sealed and read only by design. Save files to your home folder, which is on the writable Data volume.
What does Ignore ownership on this volume do?
It tells macOS to treat every file on that drive as yours. It is the quickest fix for a drive that came from another Mac and is used only by you.