How to change permissions on external hard drive on a Mac


The other day I got a call from a business client asking ‘How to change permissions on external hard drive on a Mac?’

What do file permissions mean on a Mac?

So, the first question you should ask yourself is “What are file permissions?” File permissions are a set of rules that determines who can access files, what they can do with those files, and how secure the files are. There are three levels of security setting for file permissions. These include:

Accessibility: This is the highest level of security. Only the files’ owner (the user who created it) can view or make changes to its contents.

Read-Only access: This set of security is reserved for viewing only. Users with this permission level cannot make any changes to the file.

Write-Only access: This set of security allows users with this permission level to save changes to the file but they cannot view its contents.

By default, external hard drives have a permission level of “Read-Only access” which means that users who do not own the files on it can only view their properties and make changes. To change this follow these steps:

  1. Plug in your external hard drive to your Mac
  2. Click on the Apple logo in the top left corner of your screen and select “System Preferences”
  3. Within System Preferences, click on “Sharing”.
  4. Under “Share your connection from”, make sure your external hard drive is selected (if it isn’t already) and then check the box next to “Internet Sharing”.
  5. Click on “Wi-Fi Options” under your external hard drive name and select “Password Required” from the dropdown menu next to “To computers using”
  6. Type in a password and then click OK to save your changes. You should now be able to access your files without any problems!


What causes Read-only error in Macs?

I’m here to talk about what causes read-only error and how to change permissions on external hard drive on a mac.

There are several causes of read-only error in Macs. Some common causes include:

1. Improper system shutdown

This is a very common culprit that can sometimes lead to data corruption as well as the inability for your computer to recognize your external hard drive. In order to prevent this from happening, make sure you properly shut down your computer before unplugging your external hard drive.

2. Bad sectors

This typically refers to problems with the physical components of your external hard drive, which makes it impossible for the computer to access certain parts of data on your disk. If you suspect this is the problem, try checking if Disk Utility can repair any errors with your “external” hard drive. If this does not fix the problem, it is likely that you will need to replace your external hard drive. You can check if you have bad sectors by using DriveDx.

3. Firewall

Sometimes an external hard drive could appear as “in use” because of how firewalls operate on a Mac. Make sure any applications or processes which are accessing files on your external hard drive are allowed to do so.

4. Corrupted file

If you’ve accidentally deleted or corrupted any of the files on your external hard drive, it could prevent Mac OS X from writing new files on that disk. To fix this problem, first try checking for errors with Disk Utility and repairing them if possible. If this does not work, you will need to boot your Mac from Recovery Mode (hold down Command+R on startup) and run Disk Utility from there.

These corruptions can cause the ‘Other Storage’ in Mac to report wrong data.

5. USB 3 ports

If you are connecting your external hard drive to a USB 3 port, sometimes it will only recognize the disk after several attempts of re-plugging the device in. When you connect your external hard drive via USB 3, make sure you wait for 10 seconds before giving up.

6. Unsupported format

If you are trying to access your external hard drive on a Windows machine, your data will be inaccessible if the disk is formatted for Mac (HFS+). However, it is possible to reformat using Disk Utility or third party software.

7. Write-protect

If the external hard drive you are trying to access has a write-protect switch, make sure the switch is turned ‘on’.

8. Hardware failure

Sometimes hardware can fail and need to be replaced. In this case, you’ll need to get in touch with one of our experts.


9. Faulty connection

USB cables are very fragile, so make sure both ends are firmly connected before trying to access your files.

10. Intermittent issues

If you find that the external hard drive is not accessible in some cases but accessible at other times, it may be suffering from intermittent errors that can usually be resolved by either playing around with the connection or restarting your computer.

11. File system failure

The file system in a hard disk is a data structure similar to a table in a spreadsheet, containing all information about files and folders on a disk. If there is any problem in this area, you may face read-only errors or even system failure.

This is because the file system ensures that all the files and data on a disk is arranged in a way that can be accessed quickly and easily without any underlying disk failures.

12. Corrupt RAID

If you are using a RAID (Redundant Array of Independent Disks), instead of an external hard drive, you may also face read-only errors. RAID is a technology that combines multiple disk drives into one or more logical units so that they can act as one single drive. If this is the case, you will need to enter your computer’s BIOS before you try to access any files on the external hard drive-in order to find out if it is connected to the RAID.

Mostly, people usually come across this problem when they try to create an encrypted disk image using Disk Utility in Mac OS X. Of course, you can easily change the privacy settings so that no one else but yourself can access your files.

But sometimes, even though everything seems alright with the privacy settings, users still receive “The disk you inserted was not readable by this computer” or “Read-only file system” message when trying to open the newly created disk image. This problem is probably due to permission issues with external drive. You may need administrative privileges for changing permissions of external hard drive, hence take control of it.

If you are concerned whether the permissions of external hard drive has been changed correctly, please refer to the next section.

How to change file system of a disk image?

It is possible to change a disk image from read-only base to standard HFS+ with owner permissions in Mac OS X by using Disk Utility. Please launch ‘Disk Utility’ and backup up the original disk image first because you will overwrite it during this process. Choose “Convert” at the toolbar and then select a read-only disk image as source data to convert into HFS+. Please confirm file system format change by clicking “Convert”.

How to change permissions on external hard drive on a Mac?

If you follow the steps above and change the disk image from read-only to standard, but receive an error message that says ” The item ‘.disk’ can’t be modified because it’s on a locked disk” when you try to open the file, please refer to below solutions:

1. Right click on .disk file and select “Get Info”. Then uncheck the box next to “Locked” on the pop-up information window.

2. Right click on .disk file and go to Get Info -> Sharing & Permissions under the General tab, unlock the disk by checking off Owner’s name with Mac OS Extended (Journaled) as the format type.

3. Use Disk Utility to unlock the disk by checking off Owner’s name with Mac OS Extended (Journaled) as the format type.

If you are unable to change permissions on external hard drive, then there maybe some issue with your iMac or MacBook and may require mac repairs.

I am a computer engineer holding a bachelor's degree in Computer Science, complemented by a Master's in Business Administration from University of Strathclyde, Scotland. I currently work as a Senior IT Consultant in Melbourne, Australia. With over 15 years of...