Hard Drive 'read-only' Error on Mac

In our daily lives, we rely on numerous external storage devices to transfer or store data in a more convenient and mobile way. We have become accustomed to using USB sticks, flash drives, external hard disks or SSDs. However, from time to time, after connecting the external drive to their Mac devices, users might encounter an error that allows them to only read data from the drive without being able to write or save any new files.

There are two main causes for the Hard Drive 'read-only' error on Mac - the drive is in an incompatible format (most often NTFS) or the user doesn't have sufficient privileges to perform the desired operation. The first step towards fixing the issue is to determine which one of the two possible causes is occurring on the user's system. Just open Finder, select the external drive, and press Command + I on your keyboard. Alternatively, you can right-click the drive and click on 'Get Info' from the available options. In the new window, go to the General tab and look for the Format parameter. If it is anything other than APFS, macOS Extended, or FAT 32, then the drive will need to be formatted.

Performing an external drive reformat

Keep in mind that reformatting the drive will wipe all data saved on it, so proceed with caution.

1. Connect the drive to the Mac.
2. Open the Applications folder, go to Utilities, and launch Disk Utility.
3. Choose the external drive from the Disk Utility sidebar.
4. Go to the 'Erase' tab.
5. Enter a name for the reformatted drive.
6. From the dropdown menu, select the macOS Extended (Journaled) format.
7. Click on 'Erase.'
8. The external drive will now be formatted into the correct format allowing users to write data to it.

Fixing permissions issues

If the drive is in the correct format, then users should focus on fixing potential permissions problems. 

1. Start by opening Finder and selecting the external drive.
2. Right-click the drive and select the 'Get Info' option.
3. Locate the arrow next to 'Sharing & Permissions' and click on it.
4. Go to the 'Privilige' menu located next to the username and select 'Read & Write.'
5. Close the 'Get Info' window.
6. You may need to restart the Mac for the changes to take effect.