I upgraded my mac to High Sierra without backing up my data. Then my Mac wouldn’t login, it gives me a black screen then it restarts.
So I decided to reinstall the software, but first I need to back up my data. I’ve been trying since last night. I put Mac in recovery mode, then I created a “compressed” disc image to put it on an external hard drive. I wanted to make sure I can open it before I reinstall and in the process lose all the data. I put it on a friend's Mac, and it keeps saying “no mountable file systems” and the dmg won’t open. The dmg file has a size of 500 GB.
Is there any other way to backup my data, given that I can't login into my Mac after the High Sierra install?