kernel: ... sysrq: HELP messages in log

[loeriver]

From time to time I see a message like this in my log files:

 

2025-06-05T11:29:33.367636+02:00 bananapipro2 kernel: [934985.549250] 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) show-blocked-tasks(w) dump-ftrace-buffer(z) replay-kernel-logs(R)

 

The system continues to work (although I remember that it stooped at this point in older releases).

 

Is there any action required? I am afraid that this could stop my system which is running unattended for longer periods usually.

 

I am running v25.2.2 for Banana Pi Pro running Armbian Linux 6.12.20-current-sunxi.

[IBV]

Hi,

 

it looks like you or a process is triggering the SysRq key.

For example, If I press Alt + PrtSc (SysRq) + h, I see the same message in dmesg.

 

https://en.wikipedia.org/wiki/Magic_SysRq_key

 

[djurny]

Hi @loeriver,

Check your serial console, as sending a serial <BRK> will trigger the Magic Sysrq sequence.

For example, using `tio` to connect to a serial console, I can invoke the Magic Sysrq help test with <ctrl>-t + B + <enter>.

Perhaps your serial port has it's RX line shorted to ground?

Groetjes,

[loeriver]

Hi,

thank you for your comments, at least I learned about the SysRq sequence this way.

 

I actually have no clue which process should send this sequence, an hardware issue of the RX line seems also unlikely to me (very short wire to the RS232-USB converter).

 

The only additional observations:

 

-it is a rare event, 24x7 system, most recent events:

• Jun 9th: at the end of a shutdown sequence
• Jun, 5th: no obviously related entries in syslog before it
• May, 28th: no obviously related entries in syslog before it
• May, 24th: at the end of a shutdown sequence
• May, 23rd: at the end of a shutdown sequence
• May 22nd: at the end of a shutdown sequence

-it always occurs in pairs, timestamps separated by some µs, e.g. 16:50:49.191219 and 16:50:49.191355

 

Meanwhile on v25.5.1 for Banana Pi Pro running Armbian Linux 6.12.30-current-sunxi.

 

I guess I will have to live with this effect, which is not harmful as long as the system continues to run.

 

Greetings.