Installing Arch on the Raspberry Pi is rather simple and well documented. There is an offline step, where you copy a base system on the SD card. Then, you place the card in the Raspberry Pi, boot it and you log into that new system somehow, to finish the configuration and start customizing. “Somehow” is either: you plug a keyboard and a screen to the Raspberry Pi and work within the console, or: you plug the Raspberry Pi to your router/computer through an Ethernet cable and log in over SSH. But what if all you have is a Wifi dongle?
“Hey, Pal! How are you? Remember that little project I had on the CubieTruck? I resumed hacking on it. But it’s a pity, I lost my root password… I have to start all over again. Any chance you remember what silly password we choose together?”
If only it was the user’s account password, it would be easy: log as root, change the password on behalf of the user, done. That time, who is going to save the root account? Is there any rootroot account, by any chance? No. But don’t worry, we’re going to hack into the root account nonetheless. But how? It’s Linux, it’s super secure, it’s the root account, I choose a 50-bits-of-entropy-random-super-secure password… Maybe. But almost any security will fail, once the hacker has access to the hardware. And today, we’re the hacker!