Fix Guide: External Drive "Read-Only" Error on macOS Tahoe 26.2

Symptom: You connect an NTFS, ExFAT, or APFS external drive and can see the files, but you cannot copy new files to it or delete existing ones.

Tahoe 26.2 has increased security for external volumes, often defaulting to "read-only" if the drive was not properly unmounted or if there is a permission mismatch.

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Fix 1: Force Mount with Write Permissions

If macOS mounts the drive in a "safety" mode, you can manually remount it.

1. Open Terminal.
2. Find your drive identifier:

diskutil list

1. Look for your drive (e.g., /dev/disk4s1).
2. Run:

sudo diskutil unmount /dev/diskXsY
sudo diskutil mount /dev/diskXsY

Fix 2: Repair the Drive via First Aid (Terminal)

The Disk Utility GUI can sometimes hang on Tahoe 26.2. Using the command line is more reliable.

1. Open Terminal.
2. Run the repair command (replace diskXsY with your actual ID):

sudo diskutil repairVolume /dev/diskXsY

Fix 3: Disable "Ignore Ownership" for APFS/HFS+

If the drive is formatted for Mac, you might be blocked by file-level permissions.

1. Right-click your drive on the Desktop and select Get Info.
2. Click the lock icon at the bottom right.
3. Check the box for "Ignore ownership on this volume."

Note: If your drive is NTFS, macOS cannot write to it natively without a third-party driver like Mounty or Paragon NTFS.