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I want to compress a Time Machine backup folder to a Zip file on another drive. I've set what I believe are the right preferences for Archive Utility. But when I try to run it, I immediately get "Error 13 - permission denied". It doesn't tell me whether the problem is with the source folder or the destination archive, and I don't know where to look.

I've read everything I can find on Archive Utility, but can't find the solution. Does Archive Utility need write permissions on the source item? If so, that could be my problem.

Also, what user does Archive Utility run as? Is there complete documentation for it anywhere?

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It is not a good idea to compress the folder as a zip. Time Machine uses directory hard links a lot and zip does not recognize them. So you might end up with a zip archive 10 time (or more, depending on size and modification frequency) bigger than the space your Time Machine backup originally requires. If you have to have your backup as a file, then create a compressed image from your Time Machine disk.

Open Disk Utility. Select your TM drive, and go to "File - New Image - Image of ". Then choose "compressed" in "format". Choose a location and click "save". This operation might take several hours to several days depending on the size and complexity of your backup.

If you want to do it no matter what, you have to use the command line.

sudo zip -9ry /where/you/want/zip/to/be.zip /path/to/backup/
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  • Good guidance, but I'd still like to know why I got the "Permission denied" error.
    – Rob Lewis
    Nov 22 '20 at 18:04
  • As far as I know, you can only compress a folder and have the zip file stored in the same directory (if you are using Archive Utility). I don't know which version of macOS are you using and what permissions you have set for the root directory of your drive, but I guess you need root access to create a new directory, especially considering it's a Time Machine drive. Additionally, what's inside the Time Machine backup folder has its permissions preserved, which means you can't read other user's files even if they are in Time Machine backup, you can't read certain protected system files, etc.
    – Joy Jin
    Nov 23 '20 at 0:25
  • To launch Archive Utility with root privileges, enable the root user (support.apple.com/en-us/HT204012) and do your operations logged in as the root user. I think both Finder and Archive Utility have to be launched as root for this to work.
    – Joy Jin
    Nov 23 '20 at 2:35

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