Thus, you’d need to use the ‘date’ command again but with manual specifications. That will not work if the Mac does not have internet access, however. You now have two approaches, set the date via the internet, or set the date manually. If you notice the date is completely wrong, you can set it the current date and time using a variation of the same terminal command. Pay special attention to the year as an obvious indicator of something wrong.

The entire line matters, as the date must be correct in order to install OS X, specifically the year, because if the date set is prior to the release of OS X, the error will trigger. Hit return, and if the reported date is anything other than the actual current date, then you’ve almost certainly found the cause of the problem. Pull down the “Utilities” menu option and choose “Terminal”, then type the following command into the prompt: To determine if the Terminal date trick can fix those error messages and help you to successfully install MacOS X, you’ll need to turn to the command line while at the “Install Mac OS X” boot menu. If you’re on a computer without internet access, or if you encounter the problem during an alternative OS X installation method and thus can’t access System Preferences, turning to the Terminal to set the date is the next option. That method requires the Mac to have active internet access, however. To do this, go to the  Apple menu > System Preferences > Date & Time, and be sure the “Set date and time automatically” option is checked: If you run into either error message while trying to update or install Mac OS X while from an active OS X boot (say, a standard upgrade from the App Store), you can typically resolve the problem simply by setting the Date & Time on the Mac to be determined automatically. It’s possible to encounter these errors during basically any type of installation attempt in OS X El Capitan or OS X Yosemite, ranging from the standard App Store update, using Internet Recovery, to clean installs, and using a bootable installer volume on a target Mac.

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