I know I'm late to this thread, but I do want to say that using a VM is the best and safest option as it minimizes the chances causing macOS issues. While Linux works fine for many older Macs (2007 to 2015) I still recommend using a VM, but if you want or need to install Linux on bare metal on the older 2007 - 2015 non-USB-C models, then I recommend only installing Linux to a USB drive so you don't interfere with the internal macOS boot drive (make sure to install the Linux bootloader to the external drive as well, although this is less important). Linux doesn't work very well on bare metal on the USB-C Macs:
https://github.com/Dunedan/mbp-2016-linux#keyboard--touchpad
If you ever decide to install Linux on bare metal, then I highly recommend you have a good backup of macOS and have a tested bootable macOS USB installer made while you can still boot macOS just in case Internet Recovery Mode has issues.
Another option if you need to run Linux on bare metal is to use another laptop. Just about any 64 bit Intel/AMD laptop can be used which has 4GB+ of RAM (just stay away from the low-end budget CPUs since they should never have been used with any laptop ever -- stay with Intel Core 2 Duo, or Intel i5/i7 CPUs or AMD equivalents). Usually business class laptops are best as most consumer class laptops are just cheap budget models with extremely poor CPU and RAM performance (A 20 year old 32 bit CPU with 2GB of RAM can out perform the low end budget 64 bit CPUs with 4GB of RAM in some of those low end consumer class laptops even running Linux -- I was so surprised & horrified when I had to help someone who had purchased one of those budget laptops -- it was painful).