My Raspberry Pi is connected to a Arduino over USB. I addressed it at /dev/ttyUSB0 until today. I also addressed a motor control board attached to the second USB port at /dev/ttyACM0. When I started up my Pi today it wouldn't boot. I looked at the SD card on my Mac and although I couldn't see into the Linux partition, I could see that there were files missing in the root directory. I had a backup disk image so I copied the files from it to the SD card. (I had no idea whether this was a reasonable thing to do but I was desperate.)
My Pi then booted. Everything seems to be running okay except when I do a ls /dev there is no ttyUSB0 or ttyACM0 there.
Any thoughts on what I should try next?