Running Ubuntu Server on a Raspberry Pi 3 B+ and I am unable to disable the console attached to the GPIO UART for the initial boot sequence. I am able to disable it in general execution (and have done so) but every restart it is enabled for the "Hit any key to stop autoboot" dialogue.
The board is to be placed in an autonomous vehicle, the accompanying board is constantly streaming telemetry through the interface. If it starts up first (it always does unless deliberately delayed) then the RPi is unable to boot because of that dialogue. Apart from the nuisance of the delayed start there is the obvious danger of the RPi being unable to recover in the event of a power cycle mid mission.
Ubuntu Server 18.04.4. LTS Raspberry Pi 3 B+ GPIO UART (ttyAMA0)
To disable the automatic start I did the following:
- Removed console=ttyAMA0,115200 from /boot/firmware/nobtcmd.txt
- Added dtoverlay=pi3-miniuart-bt to /boot/firmware/config.txt (or usercfg.txt, makes little difference)
- Disabled serial-getty@ttyAMA0.service
The above steps have ensured its functionality in general use only, how do I prevent the initial service from running?