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I'm experiencing a shutdown of an iMac during startup, when the progression bar almost halfway.

I tried, with no success: - starting up from the iMac recovery partition and checking the HD with Disk Utility (rebuilt permission, verified the HD) - Safe Boot - Fsck

Before attempting to reinstall Mac OS I think I need to backup the iMac first.

Any other check suggested before trying to re-install Mac OS?

Thanks for any insight!

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To attempt to back it up you could try starting in Target Disk mode & connect it to another Mac.

It is potentially safe - as you've checked the disk already with no errors - to simply overlay a new OS on top of the existing one without disturbing any other data. Run 'Install macOS' from the Recovery partition.

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  • Tetsujin, thanks for your feedback. I still have problems: I'm unable to start the Mac OS install from the Recovery, since my Apple ID+password is not being recongnized (although it works on other Macs in my office :-( ). Sep 24 '19 at 9:41
  • Tetsujin, since my Apple ID/password are not recognized by the iMac, can I run the "install macOS" from the Terminal ? Beware that I don't want to erase the HD with its data, just "overlay a new OS on top of the existing one without disturbing any other data" as you say. Sep 24 '19 at 9:54
  • You shouldn't nee ID/pass from Recovery. Are you sure it didn't go to Internet Recovery instead?
    – Tetsujin
    Sep 24 '19 at 10:45

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