How to make external hard disk read only

Probably the most reliable way to do this is with FSTAB. This file is read by OS X whenever a disk is attached, and determines how it's handled. We can use this file to tell OS X to make the disk read-only. The following process will require admin privileges.

Launch Disk Utility, select the partition you want to make read-only and Get Info on it. You'll see a line called, "Universal Unique Identifier". The string following it will be needed later.

Now launch Terminal, make sure you're logged in as an admin user, and type:

sudo vifs

You will be asked to authenticate by entering your admin password. It will not appear as you type it. Hit enter when done. This will open a text editor called VIM, and within it the FSTAB file. Using the cursor keys, scroll down to the last line in the file, and then press:

o

That's the letter, not a zero. This will cause the cursor to move down a line, and the word, "INSERT" to appear at the foot of the screen. Now, type the following:

UUID=

Then, paste that long string from Disk Utility here; make sure there's no space between the "=" and this string. The normal copy/paste operates as before in Terminal. Then, press Tab to create a space, and enter the following, pressing tab wherever <Tab> appears:

none<Tab>hfs<Tab>ro

The final "ro" is the bit that tells OS X to mount the drive read-only.

Now, hit Escape. You should end up with a line like this:

UUID=blah     none     hfs     ro

Now, type a colon, ":", then:

x

And hit enter. The file will save itself, and VIM will close. Test the changes we made by fully ejecting and detaching your external HDD, then re-attaching it. You should find that it is read-only now. You can confirm this by typing:

mount

in Terminal, and hitting Enter. Look for the line that contains the name of your HDD, and you should see, "ro" or "read-only" listed in the brackets at the end of the line.

HTH 🙂

Hi,

Is it possible to reverse this process if you wish to write to the drive again?

Thanks.

You may run into problems doing this depending on what is stored on the drive. The iTunes database files are updated constantly. Maybe ACLs would be a better way to accomplish your goal.

Beaker192 wrote:

Hi

I have an external hard disk which I store all of my iTunes on. I am trying to make it read only

iTunes will not work correctly (or at all) if the library is Read Only.