User Accounts Hide Used Disk Space in OS X

There’s nothing quite like being in the middle of an important export or a complicated render and having OS X tell you that your startup disk is almost full. It happens to the best of us. After experiencing this situation a few times, most of us know the classic locations to check to free up space:

  • Trash
  • Adobe cache files [1]
  • Downloads
  • Poke around ~/Library/Application Support
  • iTunes iOS backups

My next move is to use one of my favorite applications, Daisy Disk to give me a simple overview of what is using up the space. This trick and using other apps like it [2] are all it’s ever taken for me in the past to find the culprit taking up all the space. Recently, however, I was stumped as to why a Mac Pro I manage at work was slowly filling up all of its disk space.

This particular Mac had a 250 GB SSD installed as the boot drive. Multiple editors used it each week with Premiere Pro CC 2014 using Active Directory managed accounts and linking to projects and media on our fibre SAN. The immediate culprit of course seemed to be growing Adobe cache files. It usually is. So, I logged in as admin and hit CMD+OPT+i in the Finder and then clicked on each user’s home folder to see who had piled up too many cache files. To my surprise all the home folders added up to only about 45 GB. Disk Utility and About This Mac > Storage both reported the drive as having 140 GB out of 250 GB in use. A previous time this happened the drive had filled all the way up.

I have to admit, this threw me for a loop. Running Daisy Disk on the boot drive yielded the same result: it knew the drive was full, but reported all folders as only totalling a fraction of the ‘used’ space the system reported.

The Get Info window shows the sum of all the folders on my drive as almost 53 GB but About This Mac reports almost 140 GB being used.

The Get Info window shows the sum of all the folders on my drive as almost 53 GB but About This Mac reports almost 140 GB being used.

If you’re familiar with Unix systems you’ll know that the four folders on the root of every Macintosh HD [3] are not the whole picture. I used the du command in Terminal to list out the sizes for the hidden folders like /tmp, /bin, /usr, /var, etc. It still didn’t add up.

After calling out for help on Twitter, the guys at Daisy Disk jumped in and saved the day. The key to the problem was the multiple user accounts. [4] Because I was able to read the contents of each user’s home folder in the Finder while logged in as admin I assumed Finder was reporting the whole size of the folder. However, since only the user [5] has read/write access to the folders inside their home folder, Finder wasn’t actually able to count those, and neither was Daisy Disk. The system could see the overall disk usage and so it was reporting it correctly but I had assumed incorrectly that Finder, Daisy Disk, and du were able to see through the folders. Inside these folders I couldn’t see our usual suspects, the Adobe cache files, growing.

The Trick

The obvious way to fix this would be to log in as each editor and clear out each cache folder. As a responsible system admin while I can reset a password, I do not know each user’s password. And I did not want to deal with explaining to each editor why they now needed to reset their password.

I could have gone fancy in the terminal using sudo du and sudo rm to go about finding and cleaning the larger directories. But in my mind a task like this calls for a GUI and luckily if you have the non Mac App Store version of Daisy Disk [6] there is an option to “Scan as Admin” which essentially runs as the super user and will accurately count and report the full contents of each user’s home folder.

Problem solved.

Disclaimer: While I sing the praises of Daisy Disk in this piece I had no interaction with them other than the tweet mentioned and they have not sponsored me or this post in any way.

  1. ~/Library/Application Support/Adobe/Common/Media Cache
    ~/Library/Application Support/Adobe/Common/Media Cache Files
    ~/Documents/Adobe/[version number]/Adobe Premiere Pro Preview Files  ↩

  2. OmniDiskSweeper, Grand Perspective and Disk Inventory X are some other options.  ↩

  3. Applications, Library, System, Users  ↩

  4. If you run a machine without Active Directory accounts or multiple user accounts you likely won’t hit this issue.  ↩

  5. And, the super user (root)  ↩

  6. Bought it on the Mac App Store like me? Just download it from their site and it will recognize the purchased MAS version and act as if it were purchased. Absolutely cool.  ↩