I wrote:
> I have a machine running Fedora 41 which has stopped providing video
> for its console. Of course, the problem could be hardware, but there
> is no clear evidence of that. I am able to access the machine with SSH
> so I know it is working. I don't find any indication of a problem in
> log files. To help diagnose the issue, I'd like to access its console
> through its serial interface. (The machine does have a DB9 serial
> connector and I have verified that it works properly.)
>
> I have connected a serial to USB adapter to the machine's serial port
> and connected the other end of the USB cable to a laptop (also running
> Fedora 41). On the laptop, I've started putty and selected a serial
> connection to ttyUSB0 at speed 38400. On the problem machine, I've run
> the following commands as root with no errors reported.
>
> # grubby \
> --args="systemd.journald.forward_to_console=1 \
> console=ttyS0,38400 console=tty1" --update-kernel=ALL
> # # The line continuation above is only for readability.
> # # The actual command was all one line.
> # grubby --set-default=/boot/vmlinuz-6.13.9-200.fc41.x86_64
> # grub2-mkconfig -o /boot/grub2/grub.cfg
> # grub2-install /dev/sda
> # reboot
>
> I then SSH into the problem machine and check for agetty.
>
> # ps -ef | grep [g]etty
> root 1429 1 0 21:55 tty1 00:00:00
> /sbin/agetty -o -p -- \u --noclear - linux
> root 1430 1 0 21:55 ttyS0 00:00:00
> /sbin/agetty -o -p -- \u --keep-baud 115200,57600,38400,9600 - vt220
> # Again, lines are split and condensed here only for readability.
>
> After all this, I get no output on the putty connection and no response
> when attempting any entry. I've also tried the other listed baud rates.
>
> Is there any obvious step I've missed? Is there a better way to do this?
Roger Heflin wrote:
>If the machine does not crash then the serial console is not going to
>have any information that dmesg from ssh does not have.
>The use-case for the serial console(or kdump) is when the machine
>stops and you can no longer see dmesg output from that boot.
>
>Likely you will need to find the log file for the Wayland/X session
>and look at it.
Well, neither X nor Wayland has been started since the problem. Without
a display, neither would be of much help. I realize I could try starting
through SSH but haven't felt the need nor can I see the point. I can
start an X application with port forwarding. Note, I do not use the
"graphical" boot and start KDE from the command line.
Trying to start X through the SSH (-X) connection, I'm told, "Only
console users are allowed to run the X server". Trying to start Wayland
doesn't work either but produces voluminous output. If the serial
connection worked, it would be a console, so maybe Wayland or X could at
least try to start.
Looking through the dmesg output on the problem machine and on another
machine (also Fedora 41) with the same monitor attached, I don't find
any references to the monitor at all. It appears that monitor detection
doesn't happen until the normal syslog process is running. I do find a
reference to it in /var/log/messages, but only on the working machine.
I don't find any messages indicating failure to find the monitor on the
problem machine.
Of course, the motivation for trying to get the serial console working
is not really the reason for my post. My reason is, why doesn't the
serial console seem to work? What am I missing in the process?
I might be focusing on the serial console for Fedora when what I really
need is serial console access to the BIOS boot process. That is the only
way I see to boot from a USB drive (with a different system), just to
see if the problem is a configuration error in Fedora. I now realize
that by the time Fedora starts, that process is done. Maybe I should be
asking if there is a way to get serial access before Fedora.
--
Dave Close, Compata, Irvine CA +1 714 434 7359
d...@compata.com dhcl...@alumni.caltech.edu
"A man who says, 'I have learned enough and will learn no further,'
should be considered as knowing nothing at all." --Haile Selassie
--
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