Enable serial-getty via config.txt

[Hritik14]

I've a headless dietpi setup on rasp pi 5 and I wanted to get a serial shell for debugging.

I've the following config:

dietpi@DietPi:~$ cat /boot/dietpi.txt | grep SERIAL
CONFIG_SERIAL_CONSOLE_ENABLE=1

dietpi@DietPi:~$ cat /boot/config.txt | grep console
dtparam=uart0_console

dietpi@DietPi:~$ cat /boot/cmdline.txt
root=PARTUUID=d1fb42d0-02 rootfstype=ext4 rootwait net.ifnames=0 logo.logo console=serial0,115200 console=tty1

but since [email protected] is disabled by default, I wasn't getting a login shell.
Finally, I modified the dietpi-wifi.txt to connect to my wifi and then enable serial-getty to get login on serial.

Would it be possible to enable this by config alone ?

[Joulinar]

did you tried using dietpi-config to enable serial console?

[Hritik14]

I did not have a shell into dietpi, so no. I guess that would've worked too but I wanted to do it via config on sdcard.

[Joulinar]

you would need to do this before first boot happen. There you can configure serial console as well as wifi.

[MichaIng]

There is some dedicated issues around UART on first boot on Raspberry Pi. First of all, the primary UART adapter is/was unintentionally disabled on fresh images. Solved for next DietPi release, planned for this Saturday: 528bf2f

For Raspberry Pi 5, we additionally need to update our raspberrypi-sys-mods package, since the current one does not setup the /dev/serial0 symlink correctly on RPi 5, where it needs to point to /dev/ttyAMA10 instead of /dev/ttyS0 or /dev/ttyAMA0. I'll find time for this after next DietPi release.

CONFIG_SERIAL_CONSOLE_ENABLE only works as flag to disable the expectedly enabled UART adapter on first boot, and whether to show the dialog to disable it. It has no effect anymore afterwards. I just moved it to the correct location and added better explanation: 8418421

So to enable the serial console on the dedicated debug port of the RPi 5 on first boot, after flashing the image, before booting it:

• Edit config.txt on the FAT partition and change enable_uart=0 to enable_uart=1. Otherwise the port is disabled firmware-wise.
• Edit cmdline.txt and replace console=serial0 with console=ttyAMA10, so kernel output happens on the correct console.
• This should automatically trigger a login prompt there as well, even that the related [email protected] is not explicitly enabled. systemd does this automatically on active consoles, unless masked.

[MichaIng]

Oh, I didn't know it is broken in RPi OS as well 😅. We use an own raspberrypi-sys-mods package to skip some of the content not needed/conflicting with DietPi. Means, instead of just taking their udev rules as is, I better test them, to assure the symlink is created as expected on all RPi models. Luckily I have the 3 relevant case here:

• RPi 2 without WiFi: /dev/serial0 => /dev/ttyAMA0, /dev/serial1 => /dev/ttyS0
• RPi Zero W with WiFi: /dev/serial0 => /dev/ttyS0, /dev/serial1 => /dev/ttyAMA0
• RPi 5: /dev/serial0 => /dev/ttyAMA10, , /dev/serial1 => /dev/tty??

Though /dev/serial1 is expectedly not created anymore on recent RPi OS, since the secondary UART is used for Bluetooth on WiFi-capable RPi models, and basically useless on those without WiFi/Bluetooth adapters, since anyway only one UART device can be attached to the GPIO pins. On RPi 5 it could have a new use, to have /dev/serial0 for the dedicated debug UART port, and /dev/serial1 for an additional serial console on the GPIO pins, since the debug port requires a special adapter/cable what at least I do not own. But this could be only implemented for first boot for the RPi5-only image, and then there is no point to go with the symlinks at all, but use the true device nodes right from the start.

[Hritik14]

But this could be only implemented for first boot for the RPi5-only image

since this pi I was dealing with was kept away for sometime and I did not have an hdmi monitor to connect to, it'd be useful to enable serial via sdcard config although I did not do so on the first boot, do you think it would be possible ?

[MichaIng]

You can enable it by setting enable_uart=1 in config.txt and add console=ttyAMA10 to the end of the line in cmdline.txt. As long as the [email protected] has not been masked, the login prompt should then appear automatically.

[Hritik14]

[email protected] is masked by default, isn't it ? It's been some time since I installed, so I don't remember.

[Hritik14]

I might've disabled serial on the first boot when the dialogue presented. Dumb of me.
Thanks for help !

DietPi/dietpi.txt

Lines 65 to 67 in 1f98f96

	# Serial console: Set to "0" if you do not require a serial console. It will then be disabled automatically on first boot.
	# - If you leave it at "1", and first login does not happen on a serial console, a dialogue offers to disable it instead.
	CONFIG_SERIAL_CONSOLE_ENABLE=1