

I began to figure out what was going on and found out the following. The progress bar did not move at all, or moved very slowly.

The Mac rebooted, and it seemed that everything was going well, but it was not. But then I was facing multiple issues trying to update macOS from Mountain Lion to High Sierra via the Mac App Store.Īfter downloading a copy of macOS High Sierra from the Mac App Store, I started installing the update.

I successfully installed the macOS Mountain Lion (when using the NetBoot it automatically selects the version of macOS with which the iMac was shipped with). I thought that it would be easy to do but I was mistaken. Recently my sister asked me to reinstall the macOS High Sierra on her iMac because it stopped working correctly.
