Installing Ubuntu Linux on an old Mac Air (10 jan 18...16 jan 18)
https://www.lifewire.com/dual-boot-linux-and-mac-os-4125733
The above was a bit optimistic. It took me another five days. The trackpad (the little square in front of the keyboard that works like a mouse) didn't work properly. So I tried following the advice here
https://askubuntu.com/questions/847783/how-to-make-macbook-air-touchpad-usable#847788
and the mouse and keyboard immediately stopped working, and I had to reinstall Linux from a USB stick.
The wifi is still not working, so I plugged the computer directly into the modem.
I then had numerous issues installing bitcoin from
https://github.com/bitcoin/bitcoin
but I found all the answers to issues like
Makefile:498: recipe for target 'all-recursive' failed
online.
Now, the bitcoin daemon is running, and happily filling up my 1Tb external hard drive with blockchain. Except when it fails to connect to the network because of my dodgy USB sockets, which perhaps became unreliable as a result of bike touring with an old Mac with an inadequate case.