Mojave update stuck: administrator is creating non-ejectable disk image

While updating macOS Mojave 10.14.6 with the security and supplemental updates iMac restarted and got stuck at about 15% progress. Even after waiting for 3hrs when progress bar didn’t move I restarted the mac by holding the power button. It again reached at the same spot of 15% progress bar and it was not moving at all.

This time I restarted and I was holding the shift key. It didn’t go to safe mode.

Again restarted and pressed “COMMAND + V” for verbose mode startup. It started showing everything on terminal. This is where I found it got stuck with the message for very long time

administrator is creating non-ejectable disk image

Finally I could fix it with these steps

1. Hold Command + R on startup of macOS
2. Select the first option, Restore from Time Machine Backup
3. Before starting the update, macOS must have saved one snapshot. Choose that snapshot with date/time.
4. Accept that as restore point & restart the Mac

It will restart the Mac & now everything works fine.

These steps actually undo the process of update. Now I can choose updates one by one instead of bulk installing so many updates.

Note: While it was taking hours to apply the update I started drawing above the Mac Monitor. Marking if progress bar is moving very slow. And frustration marks above the Apple, because it was taking really very very long time.