I'm trying to update my Macbook Pro to the latest security update for High Sierra but the download doesn't seem to finish and is working in a really weird way. I tried to cancel the current update, and it does cancel, but when I try to start it again, it doesn't start from the very beginning and shows an entirely different progress than what it showed before I cancelled it. For instance, I cancelled the download at around 700mb, but when I tried up update again, it shows that only 300mb has been downloaded. I want to start the download from the start, from 0%, which I think will fix the issue but I can't seem to do that, too. Can anybody please help me? I tried to wait it out already, but it just gave me a connection error around 1.6GB. When I tried to start again, it started at around 738mb.

  • I would try a different approach and download from here: support.apple.com/en_US/downloads As far as I know High Sierra downloads tmp system updates to a file similar to this: /private/var/folders/zz/zyxvpxvq6csfxvn_n00000s0000068/C/com.apple.SoftwareUpdate/CFNetworkDownload_XxxXxX.tmp then assembles it into a subdirectory, before moving it to /Library/Updates/. You can always boot into "Recovery", which should let you browse all directories. Also a safe boot with an installation attempt there often helps.
    – Redarm
    Commented Dec 17, 2018 at 14:46

3 Answers 3


Sorry, but I only have a partial answer to your question:

First off I would try a different approach and download from here:

Also a safe boot (pressing and holding the shift button at boot until the Apple symbol appears) with an installation attempt there often succeeds.

As far as I know High Sierra downloads tmp system updates to a file, or files similar to this:
...then assembles them into a subdirectory, within... /private/var/folders/zz/zyxvpxvq6csfxvn_n00000s0000068/C/com.apple.SoftwareUpdate/swcdn.apple.com/content/downloads/
...before moving them to...

You can always boot into "Recovery", which should let you browse all directories in Terminal (to be found under the "Utilities" menu).

  • I suppose I'll go with this instead. Also, I think it worked! Deleting the files, I mean. I deleted the files in the said directories but they App Store continues as if I've deleted nothing. However, when I booted into safe mode, everything went perfectly fine.
    – Xykros
    Commented Dec 17, 2018 at 15:26
  • I've just observed the updates being downloaded to the system cache and moved the way I've described. I've never tried to actually delete them; with all the other options to fix the issue, I never saw the need.
    – Redarm
    Commented Dec 17, 2018 at 16:00
  • 1
    This was very useful, thanks. In order to delete the data from /Library/Updates/ I had to additionally disable SIP first to avoid "Operation not permitted" error, as per appletoolbox.com/… Commented Jul 31, 2019 at 9:46
  • After a normal boot, just open the Terminal, type sudo su - and enter your password. Then it's good to go and delete those files.
    – Rockallite
    Commented Nov 2, 2021 at 6:26

This seems to be due to an interrupted or corrupted download. This can usually be resolved by clearing your Mac App Store cache.

  1. Quit the Mac App Store
  2. Go to Terminal and type following: open $TMPDIR../C/com.apple.appstore/
  3. Move the files inside the folder to the Desktop or any temporary location (if you are confident, you can move them to Trash straight away.)

This should resolve the problem as temp files are cleared. For more information, read http://osxdaily.com/2016/10/08/mac-app-store-temp-cache-folder/.

If it is still not working, locate the folder /private/var/folders and open each subfolder inside it until you find com.apple.appstore. This stores the partial downloads. Do not delete any other files, only folders named com.apple.appstore.

  • 1
    This won't work. I also tried browsing folders in the /private/var/folders but I can't access some folders, so in the end I can't really delete anything. It says that I don't have the permission despite the fact that I'm using the admin account.
    – Xykros
    Commented Dec 17, 2018 at 12:22

Option Click on the install button.

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