Today I was trying to reinstall an older Mac Mini and installation keep failing with error: “This copy of the Install macOS Sierra.app application is damaged, and can’t be used to install macOS.”

I have tried Yosemite, High Sierra beta (the latest one b6) but still the same error happened so I started wondering why it would fail. One look in the terminal on date and time showed that Mini thought it’s 2001 so package couldn’t be verified and thus installed as verification failed.

So I run following command to set today’s date and time:

date 0818134217

After the date and time were updated to today’s date and installation went on without any problems.

Here is how to use date command:

NAME
date — display or set date and time

SYNOPSIS
date [-jnu] [[[mm]dd]HH]MM[[cc]yy][.ss]

So in my case it was:

  • 08 – month
  • 18 – day
  • 13 – hour
  • 42 – minutes
  • 17 – year

This might save you some time.