Installing El Capitan from OS X 10.6.8

I have this old iMac - it can run up to El Capitan and is currently running Snow Leopard 10.6.8.

From the appstore I can now only get Sierra.

Installing with an El Capitan DMG I get the error "This copy of the Install OS X El Capitan application can't be verified. It may have been corrupted or tampered with during downloading."

The DMG has been verified and is all good.

Any ideas please?

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Try back dating your machine to just after when you down loaded. Go into System Preferences > Date and Time > turn off the automatic time set and move the date back. Do your installation then reset the clock.

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Got past the error with your suggestion, installation is progressing now.

Thank you


@sunfyre Little things like that can drive you nuts trying to figure out. Glad it worked for you ;-)


If you're ever trying to install an older OS on a recently formatted hard drive using a bootable USB drive, you can use terminal to set the date back. Typically looks like this "Date 1202009152015" for December 2nd 2015 9:15am (Month)(Day)(Hour)(Minute)(Year). Apple stopped signing older OS's in what seems like January of 2016 so setting the date back anytime prior to that always works for me.


Thanks guys - installation was straight forward after changing the time.

All working fine ;)


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