Serial console - has anyone gotten this to work?

stuartbh

Active Member
Dec 2, 2019
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Hello all!

Is anyone familiar with the configuration of GRUB / Linux in pursuance of instantiating a functioning serial console?

I have SOL (Serial over LAN) enabled on my server, whereby I can SSH to the BMC on my server enter 'console 1' and have access to the console for all UEFI/BIOS related functions until I get past the GRUB screen. I get the GRUB menu and am able to select the proper boot entry on the GRUB menu. However, thereafter (when Linux begins to boot), I seem to get zero Linux boot messages on the serial console output.

The last message I get is:
Loading Linux 6.2.16-12-pve ...
Loading initial ramdisk ...
?

The question mark indicates some odd graphical character (looks like a '?" in a diamond) that appears right after the last message.


Steps I have taken thus far:

1) I ammended my /etc/default/grub configuration file as follows hereupon.

GRUB_CMDLINE_LINUX="console=tty0 console=ttyS0,115200n8"
GRUB_TERMINAL="console serial"
GRUB_SERIAL_COMMAND="serial --unit=0 --speed=115200 --word=8 --parity=no --stop=1"

I then ran sudo update-grub followed by sudo systemctl reboot

2) I did verify that the SOL and BIOS setup parameters matched those suggested in the x3650 M3 User Guide.

However, there was no appreciable change in behavior of the next boot-up of the server.

Interestingly, ProxMox does successfully boot up, that is not the issue. I just never see any output on the ttyS0 console. I am going to hook a physical serial console up and see what I see as well. All messages do appear on the VGA monitor that is plugged into the server as well.

Thanks in advance for your time and consideration regarding the instant matter before us.

Stuart
 
Last edited:
If you see garbage characters every so often, that could indicate mismatching parameters for the serial port. 8N1 is of course pretty much the standard these days. But baud rates can vary. And of course, as LnxBil points out, there always is a chance that you are talking to the wrong port.

Make sure that your BMC is in fact configured for 115200. As ridiculous as it might sound, when using things like IPMI, there still is a physical serial connection involved at some point. It's internal to your motherboard, and you never actually see the serial port exposed on a connector. But it's there. And if you don't configure all the serial port settings correctly everywhere, things simply won't work.

I have spent hours hunting down all the various BIOS and BMC settings until I finally got this to work. Every server is different. Some make this easy, others can be quite frustrating. Good luck.
 

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