GRUB and installer invisible on serial console

GRUB and installer invisible on serial console

[Ricardo Wurmus]

Hi Guix,

I just wanted to install Guix System on a server where I currently only
have remote access via serial console — and which happens to have a Guix
USB stick stuck in its USB port.  I can see the system’s UEFI output and
see that it boots from USB, but “Welcome to GRUB!” is the very last
thing I see.  There is no further output.

Our GRUB is using fancy graphics, so I wonder if that means that it has
switched to a mode that I simply can’t see over my serial connection.

Is there a way to make it start GRUB in text mode — and stay in text
mode throughout the installation?

--
Ricardo

Re: GRUB and installer invisible on serial console

[Danny Milosavljevic]

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Hi Ricardo,

> Our GRUB is using fancy graphics, so I wonder if that means that it has
> switched to a mode that I simply can’t see over my serial connection.

Yeah, gnu/bootloader.scm has "gfxterm" as default for the terminal output.
That means that serial will not be used.

Valid outputs are:

         '(console serial serial_0 serial_1 serial_2 serial_3
         gfxterm vga_text mda_text morse spkmodem)

see gnu/bootloader/grub.scm .
Multiple outputs are possible.

It's possible that serial-unit (a natural number (the com port) between 0 and 3)
and serial-speed (a natural number) also need to be set up in order to be able
to use "serial".

It's possible that there would have been an automatic UEFI console handover
in grub-efi but I guess it's being overridden by our setting.
Try having our bootloader config generator not emit "terminal_output" at all
(edit gnu/bootloader/grub.scm, search for "terminal_output" and comment that
part out).  It would be interesting whether it will automatically use a
reasonable default then.

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Re: GRUB and installer invisible on serial console

[Danny Milosavljevic]

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Also, the Linux kernel console is something independent from grub.

To test that, try adding "console=ttyS0,115200" to the operating-system's
kernel-arguments.

Currently, Guix automatically set up a getty if it detects the
"console=ttyS0" argument in /proc/cmdline .  That is supposed
to ensure some reasonable console continuity, so as soon as the Linux
kernel has a console, the userspace is also supposed to use it automatically.

It might make sense to make our grub automatically add "console=ttyS0,115200"
to the Linux command line that it already emits.

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Re: GRUB and installer invisible on serial console

[Danny Milosavljevic]

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Also, try Linux kernel option "vga=off".  Linux is supposed to automatically use
the serial port if vga is unavailable.

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Re: GRUB and installer invisible on serial console

[Brice Waegeneire]

On 2019-12-21 18:31, Ricardo Wurmus wrote:
> Hi Guix,
> 
> I just wanted to install Guix System on a server where I currently only
> have remote access via serial console — and which happens to have a 
> Guix
> USB stick stuck in its USB port.  I can see the system’s UEFI output 
> and
> see that it boots from USB, but “Welcome to GRUB!” is the very last
> thing I see.  There is no further output.
> 
> Our GRUB is using fancy graphics, so I wonder if that means that it has
> switched to a mode that I simply can’t see over my serial connection.
> 
> Is there a way to make it start GRUB in text mode — and stay in text
> mode throughout the installation?
> 
> --
> Ricardo

Hello Ricardo,

I got the same setup as you working some weeks ago with the following 
config.
I also had to tweak my BIOS settings to have a reliable serial 
connection.

--8<---------------cut here---------------start------------->8---
    (kernel-arguments
      '("quiet" "console=tty0" "console=ttyS0,115200"))

   (bootloader
     (bootloader-configuration
       (bootloader grub-efi-bootloader)
       (target "/boot/efi")
       (keyboard-layout keyboard-layout)
       (terminal-outputs '(gfxterm serial))
       (terminal-inputs '(console serial))
       (serial-unit 0)
       (serial-speed 115200)))
--8<---------------cut here---------------end--------------->8---

The order of the kernel argument "console=" is important because
« The last device will be used when you open /dev/console » [1].
And note that my baudrate is not 9600, the default value, because it's 
too slow
when displaying files. If you have a low quality serial link use the 
default.

I was wondering about writing a patch to make this kind of setup the 
default for
the image installer to allow installing Guix through a serial connection 
only.
Unfortunately such a setup will remove the current eye-candy GRUB theme.

#38580 may also interest you, it adds access to the BIOS settings from 
GRUB when
using UEFI.

[1]: 
https://www.kernel.org/doc/html/latest/admin-guide/serial-console.html
[2]: https://debbugs.gnu.org/cgi/bugreport.cgi?bug=38580

Re: GRUB and installer invisible on serial console

[Ludovic Courtès]

Hello!

Brice Waegeneire <brice@waegenei.re> skribis:

> I also had to tweak my BIOS settings to have a reliable serial 
> connection.
>
>     (kernel-arguments
>       '("quiet" "console=tty0" "console=ttyS0,115200"))
>
>    (bootloader
>      (bootloader-configuration
>        (bootloader grub-efi-bootloader)
>        (target "/boot/efi")
>        (keyboard-layout keyboard-layout)
>        (terminal-outputs '(gfxterm serial))
>        (terminal-inputs '(console serial))
>        (serial-unit 0)
>        (serial-speed 115200)))

Should we add this to the OS in (gnu system install)?  Could someone
confirm that this has the desired effect?

Thanks,
Ludo’.