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Re: Serial console on buster images



On 2019-07-28 17:41 +0200, Rainer Dorsch wrote:
> Hi,
> 
> can anybody tell if the buster armhf images automatically add a serial console 
> (e.g. for the cubox-i) or if that is a manual step?

Are you talking about whilst running the installer, or for normal
booting after the installer has run?

For the installer - it will now try to run on all the consoles the
kernel has declared 'enabled' by default. Ideally that will be both
the serial console and a frame buffer console displayed on any
connected screen, but there are few guarantees as it depends on the
combination of the firmware (uboot or UEFI and the DTB) and the kernel
and what they discover/enable by default.

At the end of the install any discovered serial consoles will be added
to the init/systemd config so you _should_ get a serial console on
boot if the install process discovered, or manually configured, one.

You can find out what the kernel does by default with 
cat /proc/consoles
(anything marked with 'E' in the brackets is enabled):
tty0                 -WU (EC p  )    4:2   (on this machine)

If your ttymxc0 is being found and enabled by the kernel, but not set up by the
installer, then that's a bug and we should work out why not.

> If manual, I assume I have to take the SD card after the installation and
> 
> in /etc/systemd/system/getty.target.wants
> # ln -s /lib/systemd/system/getty@.service getty@ttymxc0.service
> 
> Is that correct?

Sorry, I've not yet groked systemd so I have no idea how that works.
 
> I addition I assume I need to add 
> 
> # cd <mount point of sdcard>
> # echo 'setenv bootargs ${bootargs} console=ttymxc0,115200' > etc/flash-kernel/
> ubootenv.d/ttymxc0
> 
> But how do I run flash-kernel on a x86 system, which has mounted the card? Is 
> there a better way to add the bootargs?

With uboot, I'm not sure there is any substitue from actually running
on the machine and setting the bootargs there using whatever mechanism
is supplied to stop the bootloader in uboot so you can fiddle. But
someone else may know better.

With grub and UEFI you cn edit the grub config to set the kernel boot args.

Wookey
-- 
Principal hats:  Linaro, Debian, Wookware, ARM
http://wookware.org/

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