This short snippet explains how to boot from an installation medium on a Mac. The installation process itself is extensively documented for most operating systems. However most modern Macs require some additional steps to even get to the point of running a live DVD, especially if you do not have access to an original Apple keyboard. This snippet documents this process.
This process is well documented. One way of creating a bootable medium is to use balenaEtcher. Install via Homebrew:
brew cask install balenaetcher
Use it to create a bootable medium from an ISO.
Boot into recovery mode by pressing ⌘R on boot. Note that this only works reliably with Apple keyboards. Alternatively you can run
sudo nvram "recovery-boot-mode=unused"
sudo reboot
The recovery mode flag is usually removed automatically but can be unset manually via nvram -d recovery-boot-mode
or by resetting the NVRAM. [Source]
Disable System Integrity Protection [Source]
In Recovery Mode open the terminal and run
csrutil disable
Then reboot. You may reboot directly into the installation media if possible.
Boot the Installation Medium [Source]
On boot hold the ⌥ key to get into the boot menu. If you are using a non-apple keyboard you can instead run:
sudo bless -mount /Volumes/Startup_Disk_Name -setBoot
sudo reboot