perhaps to the point were you cannot even boot into the installation, you are stuck without a disk to re-install the operating system. To fix this, you would have to find another Mac to download a new ...

Apple Software Restore lets you clone your Mac even with a Signed System Volume. Here's how to use it to copy your Mac's ...

How to download and install old versions of OS X on a Mac. This method involves using a bootable USB with the macOS installation on it. This might also be the best method if you already have the ...