I wish to upgrade from Snow Leopard (10.6.8) to anything higher.
Disk Utilities repair says the disk needs to be repaired. So, I need to boot onto something other than the boot drive to run disk utilities.
I downloaded El Capitan from the App Store. It appears to be an install app. I tried diskmakerx, but it requires 10.7 or higher. Not sure how to make a bootable image from the install app in Applications.
I can't use OS X Recovery, that also requires 10.7 or higher.
These directions require the DVD media, which my parents likely never had.
Edit 1: I created a USB drive using these directions, "Option 2: Use Disk Utility." I modified a bit (El Capitan instead of Yosemite, got the BaseImage.dmg by copying and using xattr to remove the invisible bit, ..), but I have a USB key with "Mac OS Extended" format and 7.8G of stuff on it.
When I boot up holding down the option key, it doesn't show any menu to choose where to boot from, it just ignores my USB drive. When I open the "Startup Disk" system preferences dialog, it does not show the USB drive (even though it is mounted). It is plugged directly into this mac mini, not through a hub or keyboard.
I looked around for related questions (e.g., here), and found nothing relevant.
Any idea of how to debug a USB drive being ignored upon (Snow Leopard) startup?