How do I find the System Build Number or I guess it is called just the Build Number (example 18A391 or 18G87 or 18G5033 or etc. etc.) for a specific Mac OS X updates? Not upgrade, just the regular updates. Examples: Supplemental or Security or Combo or Safari, etc. etc.

I am aware of thousands of blogs and websites that published those type of informations, but let's do a practical example:

Step #1 I download this specific dmg file (Security Update 2020-006 (Mojave)) from: https://support.apple.com/kb/DL2062?viewlocale=en_US&locale=en_US

Step #2 I mount the dmg file and I extract the pkg file.

Now, I do believe that the pkg file that I just extracted from the dmg file it is some sort of xar archive file, so my question is:

using the command line, how do I unzip the xar archive file and after I unzip the archive, what specific plist file I am looking for in order to find out the exact Build Number of this specific Security Update 2020-006 update?

Thank you

  • Seems you have the tasks nicely identifed (unxar the xar archive, take the plist, look up the build numer), what have you tried so far?
    – nohillside
    Nov 20, 2020 at 14:31
  • I'm curious, what problem are you really trying to solve with this?
    – lhf
    Nov 20, 2020 at 17:23

1 Answer 1


The relevant file for that specific dmg is SecUpd2020-006Mojave.pkg/PackageInfo.

After mounting the dmg, do this:

% cd /tmp
% xar -x -f /Volumes/Security\ Update\ 2020-006/SecUpd2020-006Mojave.pkg SecUpd2020-006Mojave.pkg/PackageInfo
% grep -o 'com.apple.pkg.update.*" ' SecUpd2020-006Mojave.pkg/PackageInfo | sed 's/.*\.//'

For updates that have been automatically downloaded to /Library/Updates/, the relevant file is named *.dist. For instance, in 001-48382/001-48382.English.dist there is


and also


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