Resources on installing Linux into PowerPC Macs
This site is the best for accessing the Mac BIOS called OpenFirmware
http://ben-collins.blogspot.com/2010/08/booting-your-ibook-g4-from-usb-stick.html
Older instructions on installing Linux on Mac
https://www.debian.org/releases/jessie/powerpc/ch05s01.html.en
Best (for me) Linux Distribution for running on PPC hardware
https://ubuntu-mate.org/