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In case you are experiencing a kernel crash ([[oops]]) and have already [[Hardware testing|tested your hardware]], you should report what kernel says to the console (i.e. an [[oops]] text) to [httphttps://bugzillabugs.openvz.org/ Bugzillabug tracker]. Sometimes kernel crashes so badly that <tt>syslogd</tt> is not working and what kernel says is never written to a file. If this is the case, you have to catch what kernel says. There are several ways possible. == KDump == With RHEL6-based servers, kdump is pre-configured. See http://kb.odin.com/en/10044 to check the configuration. Dumps can be found under <code>/var/crash/</code> directory.
== Manual/Photo ==
=== Hardware setup ===
First of all you should make sure that your node has a [http[w://en.wikipedia.org/wiki/Serial_port Serial port|serial port]]. If there is no such port then
unfortunately this way is not for you.
Then you need to find a second machine with a serial port on it.
This machine will be used to collect logs from your primary machine. Further you need to acquire
so-called [http[w://en.wikipedia.org/wiki/Serial_cable Serial cable|null modem cable (a.k.a. serial cable)]] and it must be long enough to connect these two machines.
=== Software setup ===
</pre>
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{{Warning|make sure kernel command line does '''not''' contain the word '''<code>quiet</code>''', otherwise most of the kernel messages will not be printed to console.}}
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For example, in GRUB boot loader configuration file <tt>/boot/grub/grub.conf</tt> it looks like this:
<pre>
Kernel loaded with such parameters will send all kernel messages to /dev/ttyS0 (first serial port, a.k.a. COM1). If you have several ports, make sure that your null modem cable is connected to the appropriate port.
==== Receiving side ====<!--T:13-->
On the second node you should run any software that can log from /dev/ttyS0.
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It can be usual
<pre>
Save the file, then recompile the kernel:
Update your bootloader for the new updated kernel. In my case I use LILO so I just type lilo at the prompt.
Next you want your netconsole to send the request to somewhere. Load netconsole module, specifying the remote server parameters:
This will load the module with your settings. Replace your local IP address with where <tt>10.0.2.1</tt> is, <tt>eth0</tt> with your network interface card device, <tt>6666</tt> with the remote netconsole port (UDP), and <tt>10.0.2.2</tt> with your remote netconsole server IP. Also add in the mac address of your remote netconsole server, which in my case was 00:05:5D:34:11:AF. You can get the MAC address using arp utility:
Netconsole documentation is available from <tt>Documentation/networking/netconsole.txt</tt> file under your kernel source directory.
=== Setting from initrd === To log the boot process before root filesystem is mounted, network device driver and netconsole modules must be loaded from initd. RedHat 5/CentOS 5: echo 'MODULES+="<network-driver-module> netconsole "' > /etc/sysconfig/mkinitrd/netconsole chmod +x /etc/sysconfig/mkinitrd/netconsole echo 'options netconsole netconsole=<sport>@<saddr>/<dev>,<dport>@<daddr>/<dmac>' >> /etc/modprobe.conf Debian/Ubuntu: echo '<network-driver-module>' >> /etc/initramfs-tools/modules echo 'netconsole netconsole=<sport>@<saddr>/<dev>,<dport>@<daddr>/<dmac>' >> /etc/initramfs-tools/modules and rebuild initrd. === Setting up rsyslogd === /etc/rsyslog.d/netconsole.conf $template NetconsoleFile,"/var/log/netconsole/%FROMHOST%-%$NOW%.log" $template NetconsoleFormat,"%rawmsg%" $EscapeControlCharactersOnReceive off $DropTrailingLFOnReception off $RepeatedMsgReduction off $RuleSet NetconsoleRuleset *.* ?NetconsoleFile;NetconsoleFormat $RuleSet RSYSLOG_DefaultRuleset $ModLoad imudp $InputUDPServerBindRuleset NetconsoleRuleset $UDPServerRun 6666 === Setting up remote side === Set up '''netcat''' ('''nc''' on some Linux distributions) on your console server to listen on port 6666 UDP: netcat -u -l -p6666 or nc -lu 6666
or
When your kernel prints something on the console, the text will be also captured on this netconsole server.
For automatic care about capturing on console server you can use init respawn feature in this way:
==== Adding date/time to messages ====
</pre>
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For more details, see man logrotate.
=== Testing netconsole === First, check log level of console messages on OpenVZ side by:
First number should be 7 for testing. You can arrange it by:
After testing you can restore previous setting the same way.
* [[Kernel debug options]]
== External links ==
* [http://kb.odin.com/en/10044 How to configure kdump (kernel crash dump)]
[[Category:QA]]
[[Category:HOWTO]]
[[Category:Kernel]]
[[Category:Troubleshooting]]
