Don't have permission to write to disk error? Do this.

Cannot Save to External Hard Drive Error - Check Write Permissions

If you are trying to save a project (or any kind of file) to an external hard drive using a Mac and you received an error saying you do not have permission to write to the drive, you most likely have this permissions problem. 

Follow along and I'll show you how to quickly remedy this.

  1. In Finder, click on the drive you are having issues with.
  2. Press CMD - I to open the Info Window on the drive.
  3. On the bottom right, you may have a lock that is locked. Click on it to unlock it. 
  4. Enter in your username and password for your Mac. Most likely your username is filled in.
  5. On the bottom of the window there is a section that says Ignore Ownership On This Volume. Check it so you have a blue checkmark.

    *If you work in a setting where you are not the only owner, you will need to adjust or add by individual permissions under the privilege section.
  6. Click on the lock to lock from any further changes.
  7. Try saving your file again.

There you go. That should've fixed the problem for you. Let me know if that worked for you in the comments below.

 
Get Info Window on External Drive
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External Hard Drive Not Showing Up in Mac OS X

Let us go on a technical story and explain a key simple fact I overlooked.

What you see below is the Terminal app included in Mac OS X. I resorted to using this app because I have a 4TB Seagate External Hard Drive that wasn't being recognized when I am connecting it to the Trash Can Pro (Late 2013 Mac Pro.) So I went to Google and did my normal search.

Skip to the second section if you are looking for ideas of how to recognize the disk.

An option was to use the diskutil command line, which I did. I was seeing the hard drive but whenever I tried repairVolume or repairDisk nothing was being fixed. Then I found a KB article on Seagate saying to make sure the AC adaptor is plugged into the actual wall, not a power strip. I kept pulling my hair and then tried eraseDisk as seen below. 

On a random whim, I thought to change out the USB 3 cable and see if that was the issue. Son of a bitch, that was the culprit preventing this drive from showing up in Disk Utility or Finder. Swap cables our first if you have issues with your external hard drive on Mac. 

If you continue to have problems, then take/raise the appropriate levels of force gradually. No hammers kids.


Section 2 - Ideas on how to fix.

Open Terminal - CMD Spacebar and type Terminal or go to Utilities under the Applications folder and then select Terminal.

 

Type diskutil list   This lists the names of the disks and more importantly the identifier. You can see this used in the next GIF, I am targeting a disk called disk3s2.

Type diskutil list 

This lists the names of the disks and more importantly the identifier. You can see this used in the next GIF, I am targeting a disk called disk3s2.

Here I type, diskutil verifyVolume /dev/disk3s2  diskutil tells terminal I am performing a disk command. verifyVolume is the disk utility common. /dev is referring to your computer i.e. my Mac Pro.   /disk3 is the hard drive and disk3s2 is the partition of the drive I am working on.

Here I type, diskutil verifyVolume /dev/disk3s2

diskutil tells terminal I am performing a disk command. verifyVolume is the disk utility common. /dev is referring to your computer i.e. my Mac Pro. 

/disk3 is the hard drive and disk3s2 is the partition of the drive I am working on.

Using diskutil you can use other commands to work on the disks like:

repairVolume - 
example: diskutil repairVolume /dev/disk3s2

repairdisk - A whole disk must be selected to repair a disk, not just a partition.
example: diskutil repairVDisk /dev/disk3

eraseDisk JHFS+ (Note, you will need to identify the file system e.g. JHFS+ and then list the new name of the hard drive)
example: diskutil eraseDisk JHFS+ Audi S8 /dev/disks3s2

I hope this helps. This is how far I have made it in Terminal researching the internet and trying out commands.
 

You can also check out this article - Disk Management From the Command Line