Enabling a USB Serial Console on Linux (2022) | Hacker News Reader

Enabling a USB Serial Console on Linux (2022)

mattray.github.io

21 pointsGalaxySnail5 comments

For GRUB:

   GRUB_TERMINAL_INPUT="console serial"
   GRUB_SERIAL_COMMAND="serial --unit=0 --speed=115200"

* https://wiki.archlinux.org/title/working_with_the_serial_con...

* https://help.ubuntu.com/community/SerialConsoleHowto

In addition / alternatively to systemD, you can also tell the kernel about the serial console (especially for kernel boot output):

    GRUB_CMDLINE_LINUX="console=tty0 console=ttyS0,115200n8"

Also, perhaps because I'm a bit 'old fashioned', I don't really like that a lot of distros have "splash quiet" in the options: I like seeing the output. Also not have a fan of having a GRUB timeout of zero and not having a GRUB menu.

PSA: The Linux kernel will only have one console at a time during boot. This means that if both VGA and serial are specified, in that order, the last one is used, meaning there will be no output on the VGA until `getty` starts up on other VTYs.

I'm pretty sure the baud rate default can be 115200, 9600 is very late 80s.

Raspberry Pis GPIO pins include a serial port and can run at 115200. I've used that for monitoring the boot process as it can be configured to put out messages before anything goes to the screen. When the boot process halts with nothing on the screen, there may still be useful information put out to the serial port.

All the Chinese dev boards, knowing that all serial is over USB now anyway, default to 2MBaud nowadays. 115200 or even 9600 gets old very quick when you accidentally put in "dmesg" or cat same huge file...

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