If an external drive is read-only on your Mac, you can open and copy files from it, but you cannot save new files, edit existing files, or delete anything. The most common causes are a physical write-protection switch, permissions, an incompatible file system such as NTFS, or a drive that macOS has mounted as read-only because of errors.
Start by checking the drive’s format and permissions in Finder. If the drive uses NTFS, your Mac can usually read it but cannot write to it without additional software. If the format is compatible, run First Aid in Disk Utility before considering reformatting.
Quick Answer
- Check for a lock switch on the drive, SD card adapter, or enclosure.
- In Finder, select the drive and choose File > Get Info. Make sure Ignore ownership on this volume is enabled when available.
- Check the drive’s format. NTFS drives are generally read-only in macOS.
- Run First Aid in Disk Utility.
- If the drive is still read-only, copy your files elsewhere and reformat the drive using a Mac-compatible format. Reformatting erases the drive.
Do not erase or reformat the drive until you have copied any files you need.
Check for a Physical Write-Protection Lock
Some USB flash drives, SD cards, external card readers, and older drive enclosures have a small physical lock switch. When enabled, the Mac cannot write to the device.
- Eject the external drive by clicking its Eject icon in Finder’s sidebar.
- Disconnect the drive.
- Look for a switch labeled Lock, Unlock, or with a lock symbol.
- Move the switch to the unlocked position.
- Reconnect the drive and try to create a test folder.
If you are using an SD card in a USB adapter, check the lock switch on the SD card itself and on the adapter. Some damaged cards can also behave as permanently locked to protect existing data. If the drive remains read-only on multiple computers, it may be failing.
Check Finder Permissions
macOS can prevent your account from writing to a drive because of its ownership and permission settings.
- Open Finder.
- Select the external drive in the sidebar.
- Choose File > Get Info, or press Command-I.
- Expand Sharing & Permissions near the bottom of the window.
- Click the padlock and authenticate with your Mac password or another available authentication method.
- Click the action menu button with three dots, then choose Apply to enclosed items if the option is available.
- Check the privilege next to your user account. It should say Read & Write.
- If it says Read only, click the privilege and choose Read & Write.
You may also see Ignore ownership on this volume. If available, enable it when the drive is used by your Mac and you need your account to manage its files. This setting is especially useful for drives moved between Macs.
If macOS will not let you change permissions
A permissions change may not work when:
- The drive is formatted as NTFS.
- The drive is mounted as read-only because of file-system errors.
- The device has hardware write protection.
- The drive is encrypted or controlled by third-party software.
- Your account does not have administrator privileges.
In these cases, continue with the format and Disk Utility checks below rather than repeatedly changing permissions.
Check the External Drive’s Format
The file system determines how macOS stores and manages files on the drive. To check it:
- Select the drive in Finder.
- Press Command-I to open Get Info.
- Find the Format entry under General.
Common formats include:
- APFS: Designed for modern Mac storage. It supports reading and writing on Macs.
- Mac OS Extended (Journaled): An older Mac format that supports reading and writing on Macs.
- exFAT: Useful when the drive must work with both Mac and Windows computers. It supports reading and writing on both systems.
- FAT32: Compatible with many devices, but it has a 4 GB maximum file-size limit.
- NTFS: Commonly used by Windows. macOS can generally read NTFS but does not natively write to it.
What to do if the drive uses NTFS
If the drive is NTFS and you need to keep its current files, copy those files to another location using your Mac. You can then either:
- Connect the drive to a Windows computer to write to it.
- Install reputable third-party NTFS software from a trusted developer.
- Reformat the drive as exFAT if you need Mac and Windows compatibility.
- Reformat it as APFS or Mac OS Extended if it will be used only with Macs.
Third-party file-system software can affect access to your data. Keep a backup before installing it, updating it, or uninstalling it.
If you decide to change the file system, see this guide to format an external drive on a Mac. Formatting permanently erases the selected volume.
Run First Aid in Disk Utility
Disk Utility’s First Aid feature checks the drive’s file-system structure and attempts to repair certain errors. It does not recover deleted files, and it cannot repair every hardware failure.
Before starting, close files and apps that are using the external drive. Repair operations can interrupt access to the drive, and unsaved changes may be lost.
- Open Disk Utility. You can find it in Applications > Utilities, or search for it with Spotlight.
- Choose View > Show All Devices in the menu bar.
- In the sidebar, select the external drive’s volume beneath the physical drive.
- Click First Aid in the toolbar.
- Read the warning, then click Run.
- Wait for the check and repair process to finish.
- If Disk Utility reports a problem, follow its recommendation.
If the volume-level check finishes successfully but the drive is still read-only, select the physical drive in the sidebar and run First Aid there as well. Disk Utility may list a device, a container, and one or more volumes. Work from the volume upward, and avoid clicking Erase unless you have a backup.
After First Aid finishes, eject the drive and reconnect it. Test it by creating a temporary folder, then delete the folder after confirming that writing works.
Check Whether the Drive Is Mounted as Read-Only
A drive can have a writable format but still be mounted as read-only after macOS detects file-system problems. Disk Utility may show a warning, or the volume may appear normal in Finder while refusing all changes.
First, safely eject the drive and reconnect it. If that does not help, run First Aid. Do not repeatedly disconnect a drive while files are being copied or saved, because that can make file-system damage worse.
If First Aid cannot repair the volume:
- Stop writing to the drive.
- Copy any accessible files to another drive or cloud storage.
- Try the drive with a different cable, port, or compatible computer.
- Consider erasing and reformatting the drive only after confirming that your backup is complete.
If the drive contains important files and cannot be repaired, professional data recovery may be safer than repeated repair attempts.
Try a Different Cable, Port, or Enclosure
A bad cable, loose connection, underpowered hub, or failing enclosure can cause unusual drive behavior, including mounting problems and read-only access.
Try these checks:
- Disconnect the drive.
- Connect it directly to the Mac instead of through a hub or adapter.
- Use a different compatible cable.
- Try another port on the Mac.
- If the drive has a separate power adapter, confirm that it is connected.
- Test the drive on another computer, if available.
If the drive works normally with another cable or port, replace the faulty accessory. If it is read-only everywhere, the problem is more likely to be the drive, its file system, or physical write protection.
Reformat the Drive as a Last Resort
Reformatting creates a new file system and can resolve persistent compatibility or structural problems. It also erases the selected volume, so this step requires a complete backup.
Choose a format based on how you will use the drive:
- APFS: Best when the drive is primarily for Macs.
- Mac OS Extended (Journaled): Useful for compatibility with older Mac systems and certain older storage devices.
- exFAT: Best when the drive must be writable on both macOS and Windows.
- FAT32: Suitable for older devices, but not for files larger than 4 GB.
To erase the drive:
- Copy all needed files to another storage location.
- Open Disk Utility.
- Choose View > Show All Devices.
- Select the physical external drive or the volume you want to erase.
- Click Erase.
- Enter a name.
- Choose a format and, if shown, a partition scheme such as GUID Partition Map.
- Click Erase, then Done.
Warning: Selecting the wrong device can erase your Mac’s internal storage or another connected drive. Confirm the drive’s name and capacity before proceeding.
If you need separate Mac and Windows partitions, review how to partition an external drive on a Mac.
Troubleshooting
The drive says “You can only read”
Check the drive format first. NTFS is the most common reason a drive is readable but not writable on a Mac. If it is not NTFS, inspect Finder permissions and run First Aid.
“Ignore ownership on this volume” is missing
This option is not available for every file system or volume type. It may also be unavailable when the drive is mounted read-only. Confirm the format and repair the volume before treating this as a permissions problem.
First Aid reports that the disk cannot be repaired
Copy as much data as possible before doing anything else. Then try a different cable, port, or computer. If the data is important, consider professional recovery. Erasing the drive may make recovery more difficult.
The drive works on Windows but not on the Mac
Check whether the drive uses NTFS. Windows can normally write to NTFS, while macOS usually cannot without additional software. Back up the files before changing the format.
The drive became read-only after an unsafe disconnection
Run First Aid and avoid disconnecting the drive while it is active. In the future, eject it in Finder before unplugging it. For more guidance, see how to safely eject an external drive on a Mac.
The drive is full
A nearly full drive may fail to save new files even when it is technically writable. Delete or move unnecessary files only after confirming that the drive is not failing. You can also check the drive’s available space before troubleshooting further.
Frequently Asked Questions
Why is my external hard drive read-only on my Mac?
The drive may use NTFS, have incorrect permissions, be physically locked, or have file-system errors. A failing drive can also mount as read-only to protect existing data.
Can I change an NTFS drive to writable without erasing it?
Usually, yes, by using trusted third-party NTFS software or writing to the drive from Windows. Back up the drive first because software changes and file-system problems can cause data loss.
Will changing permissions erase my files?
Changing Finder permissions normally does not erase files. However, applying permissions to enclosed items changes access settings throughout the selected volume, so use it carefully.
Does reformatting fix a read-only drive?
It can fix file-system incompatibility and certain structural problems, but reformatting erases the volume. It cannot repair failing hardware or recover files that have not been backed up.
Should I use APFS or exFAT?
Use APFS if the drive will mainly be used with Macs. Use exFAT when you need to write files from both Macs and Windows PCs.
Final Thoughts
A read-only external drive is usually caused by an incompatible format, permissions, physical write protection, or file-system problems. Check those causes in that order, run First Aid when appropriate, and keep a backup before making repairs. Reformat only after confirming that you no longer need the existing data.