Six Lessons Learned from Dealing with an iMac's Dead SSD

[ace (Adam Engst)]

In another thread, @Simon just shed some light on one of my mysteries—why my Mojave installer claimed it was corrupted.

Redownload Archived macOS Installers to Address Expired Certificates

I had exactly the same thing happen to me despite downloading a brand new Mojave installer. Then I realized, the problem is launching the installer off an external HDD. As soon as I moved it back onto my internal boot SSD, it launched just fine. Does this make any sense? Also, assuming this can’t be remedied, it indicates I cannot use this copy on an external drive as a rescue installer. Perhaps its only use to me is to make a bootable USB stick that I in an emergency would use to boot from a…

Since my external SSD was empty, I didn’t even think to copy the Mojave installer to the SSD and install from there. Why would the installer care where it was being launched from?