iMac restart problem

You might start by running Disk Utility's First Aid on the drive device and any containers and volumes that it holds.

With luck the problem will be fixed with that. To repair the startup drive, you will have to boot from recovery.

How to repair a Mac storage device with Disk Utility - Apple Support

If First Aid does not solve the problem, and since you normally use the Ventura OS and only sometime the Mojave, I suggest you install Mojave on an external drive dedicated to that OS and move whatever apps and files you use with Mojave to that drive.

Then erase the iMac's internal drive and reinstall Ventura and you associated apps and files.

Keep them separate. It's a small nuisance, but will prevent what just happened.

kenfrompershore wrote:

On checking finder I can see the Ventura volume, but it is totally empty.

That is because Mojave does not understand the new drive layout utilized by macOS 10.15+ where the system & data volumes are now separate. When using Mojave to access a Ventura volume, you may need to mount the "Data" volume first, then navigate to that "Data" volume in the Finder.

Since Apple has kept changing the naming & behavior of these system & data volumes with each new version of macOS, I'm not sure what Mojave may see. However, you should find the Ventura volume mounted at "/Volumes" with either a name of "Data", or "Macintosh HD - Data" (these are the defaults), unless you modified the "Macintosh HD" portion of the name.

You definitely will not find any data within the "Users" folder of the Ventura system volume since that folder is used to mount the separate Ventura "Data" volume. The "Users" folder holding your home user folders will be found on the "Data" or "Macintosh HD - Data" volume which is mounted at "/Volumes".

Yes it sounds like you need to Reinstall Ventura, then Restore from Time Machine.

Recover all your files from a Time Machine backup - Apple Support

Not knowing why that Ventura boot volume was wiped, failed or corrupted..?

I would run Disk Utility Repair on it before Reinstalling and Restoring.

Repair a storage device in Disk Utility on Mac - Apple Support

In Disk Utility, click View > Show All Devices.

ANARGET wrote:

Not sure if this was the problem, but my layout is different. I only have volumes listed, no container as shown. I had MacIntosh HD-Data, Mojave & Ventura.I don't seem to have a container.

Not sure if this was the problem, but my layout is different. I only have volumes listed, no container as shown. I had MacIntosh HD-Data, Mojave & Ventura.I don't seem to have a container.

👍 I was off working on a different matter.

That's ok, it seems to installing Ventura now, although it's saying over 4 hours. I think the initial problem was caused by the internet recovery connecting to the US. It's now showing GB.