Does sysrq work over USB?

[Marc SCHAEFER]

On Tue, Nov 16, 2021 at 10:29:00PM +0100, Valentin Vidi?? wrote:
> Do you have console=ttyUSB0,... set? What does /proc/consoles say?

No, I did not.

Now, I have added on a test machine:

   console=ttyUSB0,9600 console=tty0

to /etc/default/grub and started upgrade-grub and rebooted.

I had and I still have:

   root at gluster-1:~# cat /proc/consoles 
   tty0                 -WU (EC p  )    4:1

However, the command line seems correct and multiple console= are
valid [1]:

   root at gluster-1:~# cat /proc/cmdline 
   BOOT_IMAGE=/vmlinuz-4.19.0-18-amd64 root=/dev/mapper/vg1-root ro console=ttyUSB0,9600 console=tty0 quiet raid0.default_layout=1

It does not seem to be work for some reason.

Let's try with one ttyUSB console specification only: does not
boot anymore. Does not print anything on ttyUSB0. Had to recover
using a grub kernel command line edition at boot time.

Any idea?

NB: the USB serial port works with cu bidirectionnally once the
system is booted, but %break has no effect.

[1] https://www.kernel.org/doc/html/latest/admin-guide/serial-console.html