Unable to Boot up following upgrade of MacOS
Hi guys,
my MAC has been stuck for months failing to boot up with the following message:
MacBook Pro 15″, OS X 10.11
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Almost exactly one year ago the certificates for several macOS's expired.
This look like you are trying to install an OS with an expired certificate.
Apple updated the certificates so you can download High Sierra again.
Open Safari and click on the link below, Firefox will not work,
How to upgrade to macOS High Sierra - Apple Support
Go to Section 4 and click on Get macOS High Sierra
you will be redirected to the App Store High Sierra page.
It should say Get or Download.
This will download Install High Sierra.app directly to your Applications
folder. Using that and Terminal you can create a bootable USB installer.
How to create a bootable installer for macOS – Apple Support
If the App Store says ‘Open’ then it is detecting a previous download of the install app
go to the Applications folder locate Install macOS High Sierra.app.
Move it to the Trash, empty the Trash.
Restart, click on the link again, the App Store should say ‘Get' or 'Download'.
If your mac has an operating system on it then you can just set the Date & Time
to a date before October 2019 and your older installer will install.
When installed you can then set the Date & Time back to todays date.