I have a 21.5 inch late 2012 iMac and I wanted to perform a clean clean MacOS Sierra install. I followed the usual steps in setting up a USB for installation, up to the reformatting/erasing of the hard drive in preparation for the actual OS install.
After following everything I did with previous USB clean installs, I got the error “Installation Fail: The installer payload failed signature check”. I tried different solutions I found on the web but to no avail.
So, it seems that the clean install from a MacOS Sierra USB no longer works. So here is what I did instead:
- Restore my iMac to factory settings and with the operating system that came with the iMac.
- Restart the iMac in recovery mode. Restart the iMac and hold down the Command and R keys while the iMac is restarting.
- Use Disk Utility to erase the hard drive. Click on Disk Utility – Continue. Select the main volume and click Unmount then Erase. Quit Disk Utility (Disk Utility > Quit Disk Utility).
- Click Reinstall OS X and continue. Follow the on-screen instructions to reinstall Mac OS X.
- Once the original OS has been reinstalled, boot up normally, finish all the setup questions just like when you had a new iMac. Open the App Store, search for MacOS Sierra, download and install.
This may not be as clean as I have wanted but it’s the closest I can get to having a clean install, not that the USB boot option might no longer be working with MacOS Sierra.