Hello everyone. My iMac had a Samsung SSD 850 EVO 1TB completely upgraded to High Sierra APFS. Only one "partition" in that, the usual Macintosh HD, of 1TB. Yesterday I wanted to partition it and install Ubuntu. Using Disk Utility was impossibile to do that because of the structure of the container: it could't be resized. So I downloaded Paragon Hard Disk Manager that I previously used some time ago and that did well. I managed to reside the APFS partition from 1TB to 850GB and the remaining 150GB I formatted in MacOS Extended. And this is it, just 2 things: resize, format new partition. I rebooted the Mac and the nightmare began. Instead of the usual Apple logo, an icon with question mark inside a folder appeared. After this, I tried everything to access at least Recovery Mode. Nothing, it wasn't accessibile anymore. I had all the USB keys of the previous macOS installers: Mavericks, Yosemite, Sierra, High Sierra. Among these, only Yosemite worked... And this is also strange. Of course from Disk Utility I couldn't do anything with the APFS partition because APFS wasn't still invented at the time of Yosemite. Since I tried everything for hours, I decided to boot from Yosemite USB key and install Yosemite in the partition I had reserved to Ubuntu. At least I could do something from inside the disk. So I installed Yosemite, I checked how was my disk using diskutil list and the situation was as below: I then updated to High Sierra in order to have full access to APFS partition and the situation using diskutil list was as below: disk0s2 is my main partition called "Macintosh HD" disk0s3 it's my second partition called "Mac" that was originally partitioned for Ubuntu and now used for running High Sierra As you can see, disk0s2 has a +ERROR in the container scheme. It seems like all data are there but no more recognizable. It seems to be a simple scheme error, but I don't know.... That partition is de-activated and there's no way to re-activate it. It's just greyed out in the Disk Utility, so it can't be used. What do you suggest? How can I repair, fix or do something to that partition in order to access it again? I just resized it of 150 GB, damn it..... This new APFS file system is too fragile :-( Please help me if you can, thank you!