On Fri, Oct 15, 2021 at 09:02:50PM +0200, Marc SCHAEFER wrote: > Should I abandon all hope to make it work with USB, or should it work?
Yes, sysrq can work with USB, but not with stock Debian kernels, because of [1]. Here is the work-around: 1) recompile kernel (see [2]) with the following options: CONFIG_USB=y CONFIG_USB_SERIAL=y CONFIG_USB_SERIAL_CONSOLE=y CONFIG_U_SERIAL_CONSOLE=y 2) configure /etc/default/grub with console=ttyUSB0,9600 console=tty0 and run upgrade-grub 3) I then get: # cat /proc/consoles tty0 -WU (EC p ) 4:1 ttyUSB0 -W- (E p ) 188:0 and I can then do sysrq from USB: schaefer@acer-1:~$ cu -l ttyUSB0 -s 9600 Connected. ~%break [ 1633.701624] sysrq: HELP : loglevel(0-9) reboot(b) crash(c) terminate-all-tasks(e) memory-full-oom-kill(f) kill-all-tasks(i) thaw-filesystems(j) sak(k) show-backtrace-all-active-cpus(l) show-memory-usage(m) nice-all-RT-tasks(n) poweroff(o) show-registers(p) show-all-timers(q) unraw(r) sync(s) show-task-states(t) unmount(u) force-fb(V) show-blocked-tasks(w) dump-ftrace-buffer(z) Also, the HDMI console still works (logs & sysrq). The problem and solution was found with help from the kernel-newbies mailing-list. [1] https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=868352 [2] https://wiki.debian.org/BuildADebianKernelPackage