I was gifted a 2011 Mac Mini and I decided to try and get the thing up and running with a recent enough version of MacOS. When I turned the thing on, I was greeted with a fast boot to grub, indicating CentOS 7 was installed.
In my efforts to get the thing to boot from my bootable USB drive, I have been completely unsuccessful. I've tried multiple different key commands at boot up (Option+R, Command+Option+R, Shift+command+option+R, c, t) all offer the same behavior: a speed boot back to the grub bootloader. My assumption is that the recovery partition was nuked when the previous owner threw linux on this thing, but I'm not entirely sure how I can repair this. My original thought was to try and get the thing into Target Disk mode, but no joy.
Is there another path forward or will I likely need to pull the drive out, wipe it and maybe throw it in another mac to format the thing?
EDIT: So, despite having used this keyboard to boot OTHER macs into recovery mode, this one needed an entirely different keyboard. Key presses were not recognized at boot but now are. I appreciate everyone who provided feedback about this.
Best Answer
If you have an bootable macOS installer USB (Here is how to make one), boot from the installer directly by holding Option Key.
The options would require having access to a Mac (VM or real)
Another option could be to install macOS on an external drive and boot from it(holding option while booting), and try to install macOS on the internal disk.
Third option could be, remove internal disk from the MacMini, get a 2.5inch SATA to USB adapter, install macOS on the "external disk". Reinstall, and auto boot from the newly installed macOS HDD(or SSD). Might be a good opportunity to upgrade to a SSD.