Question

Hello,
I have connected a RUTX11 to a PC via a serial cable in order to obtain a backtrace of a kernel crash. On the PC:
cu -l /dev/serial/by-id/usb-FTDI_USB_Null_Modem_Cable_FTBF9K71-if00-port0 -s 115200
gives a console (login password shell all fine) but the kernel messages aren't displayed. They should, according to the Linux kernel documentation (char device major 5 minor 1).

cat /proc/cmdline doesn't indicate that the console is restricted to /dev/ttyMSM0. Is there something special to be done to enable this output ? Another way to obtain this backtrace ?
Regards,

Answer 1

Hello.

If you are connected but don't see any data there are two possible culprits.

First check your baud rate. Baud rate is the most important setting to match up.  The other culprit could be that the TX and RX lines are reversed.

Best regards.

Comments

Hello,

Data comes in, I can log in enter commands (with echo). This is not a baud rate issue, nor a RX-TX inversion.

What is missing is the kernel messages, specifically a backtrace after a kernel crash. Hard to debug without this information.

Regards,

---

Hello,

Use this command to display kernel messages: dmesg

Also you can use logread command to read system messages, for example: logread | grep dhcp

Regards.

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No, both become unusable if the kernel crashes.

Is there a way to get and analyse a kernel crash dump on this device ?

Regards,

---

Hi,

Please share the version of firmware you are using and explain why kernel crashes and steps to reproduce.

Regards

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Version; RUTX_R_00.02.04.3

To replicate the kernel crash:

  install the wireguard package

  create a wireguard interface, assign a private key listen port and IP address

 create a peer, assign a public key, allowed IPs, a pre-shared key, endpoint host and port, set route allowed IP, set a persistent keepalive

Then enable the interface. The kernel crash is immediate.

Regards,

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Hello.

Sorry for late response.

The router uses a stable kernel. I followed the steps you described but was unable to reproduce your problem.

Is there a way to get and analyse a kernel crash dump on this device?

Unfortunately, there is no such tool.

Regards.

 

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Hello,

I agree 4.14.171 is a stable kernel, but the wireguard module Teltonika uses is somewhat old.

I have recompiled a 1.0.20200729 version using the SDK, this one works fine.

If you are interested, I can PM you a wireguard config which should trigger the bug (same destination router as the one I use).

Regards,

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Hello.

Of course, send me your config via private messages. If I am able to reproduce the problem you described, I will immediately forward this information to the RnD department.

Kind regards.

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Hello Igor,

Have you been able to replicate the issue with the parameters I have sent by PM ?

Regards,