Kernel Crash Trace Log: Difference between revisions

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== Server1 configuration ==
== Server1 configuration ==


* Run the following command to load netconsole module
Insert the following line to GRUB_CMDLINE_LINUX_DEFAULT in /etc/default/grub
<pre>modprobe netconsole netconsole=@10.10.10.1/,@10.10.10.2/</pre>
or with MAC address (MAC address is needed if a switch doesn't allow broadcast or server2 is in another network, i.e. behind a router)
<pre>modprobe netconsole netconsole=@10.10.10.1/,@10.10.10.2/xx:xx:xx:xx:xx:xx</pre> where xx:xx:xx:xx:xx:xx - MAC address of server2 or MAC address of the router
* Check "modinfo netconsole" and https://www.kernel.org/doc/Documentation/networking/netconsole.txt for more information


=== Find out MAC address ===
netconsole=<port>@<your ip>/eth0,<port>@<remote logging ip>/<mac address of logging pc> loglevel=7


# <pre>ping 10.10.10.2</pre> or "ping default_gateway_IP", check "ip route | grep default" for the IP
The hole line locks like this.
# <pre>arp -n 10.10.10.2</pre> or "arp -n default_gateway_IP"
GRUB_CMDLINE_LINUX_DEFAULT="quiet netconsole=5555@192.168.18.81/eth0,5555@192.168.16.32/0c:c4:7a:44:1e:fe loglevel=7"
 
* Check https://www.kernel.org/doc/Documentation/networking/netconsole.txt for more information
 
To find out your MAC address use on the logging Server/Laptop
ip a


== Server2 configuration ==
== Server2 configuration ==

Revision as of 14:17, 28 November 2016

Introduction

  • Sometimes you are not able to get a trace log of crashed kernel because it is not written into any file in a filesystem. This guide is aimed to help with getting a kernel crash log.
  • The easiest way to archive the goal is to utilize a remote system through network. This example shows the case with two Proxmox VE 2.X hosts. One of them (server1) is the host to debug and another one (server2) is the host to catch a log.
  • Server1 IP: 10.10.10.1
  • Server2 IP: 10.10.10.2

Server1 configuration

Insert the following line to GRUB_CMDLINE_LINUX_DEFAULT in /etc/default/grub

netconsole=<port>@<your ip>/eth0,<port>@<remote logging ip>/<mac address of logging pc> loglevel=7

The hole line locks like this. GRUB_CMDLINE_LINUX_DEFAULT="quiet netconsole=5555@192.168.18.81/eth0,5555@192.168.16.32/0c:c4:7a:44:1e:fe loglevel=7"

To find out your MAC address use on the logging Server/Laptop 

ip a

Server2 configuration

  1. Create a new file /etc/rsyslog.d/01-netconsole-collector.conf with the following content: 
    # Start UDP server on port 6666
$ModLoad imudp
$UDPServerRun 6666

# Define templates
$template NetconsoleFile,"/var/log/netconsole/%fromhost-ip%.log"
$template NetconsoleFormat,"%rawmsg%"

# Accept endline characters (unfortunatelly these options are global)
$EscapeControlCharactersOnReceive off
$DropTrailingLFOnReception off

# Store collected logs using templates without local ones
:fromhost-ip, !isequal, "127.0.0.1"     ?NetconsoleFile;NetconsoleFormat

# Discard logs match the rule above
& ~
  2. Restart rsyslog 
    /etc/init.d/rsyslog restart
  • Note: it's good idea to disable this configuration after you have done with debugging because $EscapeControlCharactersOnReceive and $DropTrailingLFOnReception are global options and they change default behaviour of rsyslog.
mv /etc/rsyslog.d/01-netconsole-collector.conf /etc/rsyslog.d/01-netconsole-collector.conf.disabled
/etc/init.d/rsyslog restart

Examination

  • We can check if everything works by causing kernel crash intentionally (be careful!, it's going to be a real crash), type the following command on server1
echo c > /proc/sysrq-trigger
  • Server1 will crash and you should get a crash log in /var/log/netconsole/10.10.10.1.log on server2
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