macOS External Drive Permissions Reset to Read Only: Fix in 3 Steps

Why Your External Drive Went Read-Only (and Why It's Not Your Fault)

You plug in your external SSD or hard drive—maybe a Samsung T7 or an old Seagate Backup Plus—and macOS shows it as read-only. You can't create new files, delete old ones, or even rename a folder. I’ve seen this on Monterey, Ventura, and Sonoma. The good news: you don’t need to reformat or buy a new drive.

This happens when macOS loses its permission mapping for the volume. It can be triggered by:

• Unplugging the drive without ejecting first (we’ve all done it)
• A macOS update that resets system security policies
• Drive partition map corruption (less common, but real)

Below is a three-step troubleshooting flow. Start with the first fix—it works about 40% of the time. If not, move to step two. The advanced fix is for stubborn cases.

Fix #1: Remount the Drive (Takes 30 Seconds)

1. Eject the drive properly: right-click it in Finder and choose Eject. Wait for it to disappear from the desktop.
2. Unplug the USB or Thunderbolt cable.
3. Wait 10 seconds, then plug it back in.

That’s it. If the drive mounts normally and shows read-write, you’re done. This works because macOS sometimes gets confused about the mount status after an improper disconnect. A clean remount resets the internal flags.

Fix #2: Check & Reset Permissions via Get Info (5 Minutes)

If the remount didn’t help, the permissions are likely set wrong. Here’s how to fix them without touching Terminal.

1. Open Finder and locate the external drive.
2. Right-click the drive icon and select Get Info (or press Cmd+I).
3. At the bottom of the Info window, look for Sharing & Permissions. If it’s collapsed, click the arrow to expand it.
4. Check the row for you (your username). If it says Read only, click the lock icon in the bottom-right corner and enter your admin password.
5. Change your permission from Read only to Read & Write using the dropdown.
6. If there’s a gear icon, click it and select Apply to enclosed items. This fixes all subfolders and files.

One gotcha: If the drive is formatted as NTFS, macOS can’t write to it natively. But that’s a different problem—you’d need third-party software like Paragon NTFS or Microsoft’s NTFS for Mac. For APFS or HFS+ drives, this step usually works.

Fix #3: Repair Disk Structure Using Disk Utility (15+ Minutes)

If permissions still show read-only or the drive won’t mount with write access, the partition map or volume structure might be damaged. Disk Utility’s First Aid is your friend.

1. Open Disk Utility (from Applications > Utilities, or search with Spotlight).
2. In the sidebar, click View (top-left) and select Show All Devices. This shows the physical disk and its partitions.
3. Select the physical disk (the top-level entry, usually with the manufacturer name, like “Samsung Portable SSD T7”).
4. Click First Aid, then Run. This checks the partition map for errors.
5. First Aid will run—could take 5–15 minutes depending on drive size and how badly it’s corrupted. If it finds issues, it will attempt to fix them.
6. Once done, select the volume (the one with the drive name, like “My Backup”) and run First Aid again.

After this, eject the drive and reconnect it. It should appear as read-write now.

If First Aid Fails or Shows “Invalid Name”

You might see an error like “Disk Utility can’t repair this disk” or “Invalid B-tree node”. That’s a deeper corruption. Your last shot before reformatting is to force a mount in read-write mode via Terminal:

sudo mount -o remount,rw /Volumes/YourDriveName

Replace YourDriveName with the actual name of your drive (spaces need backslashes or quotes). For example:

sudo mount -o remount,rw /Volumes/My\ Backup

If that doesn’t work, you’re likely looking at a dying drive or a file system macOS can’t repair. Back up what you can, then consider reformatting to APFS (if it’s only used with Mac) or exFAT (if you need Windows compatibility too).

One More Thing: Check the Cable & Port

This tripped me up the first time too. Sometimes a loose USB-C cable can cause macOS to read-only mount the drive as a safety precaution. Swap the cable or try a different port (USB-A vs USB-C, for example). I’ve seen cheap cables behave like this.

When to Call It Quits

If none of these steps work, your drive’s physical hardware might be failing. Copy your data to another drive immediately—use a utility like Carbon Copy Cloner or SuperDuper that can handle read-only volumes. Then check the drive’s SMART status if it’s a standard hard drive (SSDs don’t have reliable SMART data). If the drive is under warranty, contact the manufacturer before doing anything else.

Most people will be fine after step two. Don’t jump straight to Disk Utility unless you have to. Save the repair for when it’s actually needed.