Let’s talk about shrinking the APFS partition, or container, first. Locating your APFS container prior to resizing it Resizd Your APFS Container (the Hard Way) Note that my APFS container is named /dev/disk1, and resides at /dev/disk0s2. Once there, issue this command to find out where your APFS container lives: diskutil list To do this, you’ll need to open Terminal from Applications -> Utilities. For now, though, the Terminal is our friend. It’s a pretty common requirement, so Cupertino is bound to incorporate it more easily into the final version of macOS 10.13 High Sierra.

I’m confident that by the time High Sierra ships in the fall, this will be possible within the graphical Disk Utility. Of course, if you haven’t already migrated over to APFS, you might want to look into that first, with the help of John Martellaro.

You can’t currently do this from Disk Utility, so it requires some Terminal geekery. If you’re running one of the macOS High Sierra betas and have tried to resize your APFS container without success, I’ve got the answer for you.

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