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In case you are experiencing a kernel crash ([[oops]]) and have already [[Troubleshooting:Hardwaretesting|checked 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 it 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 [[w: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 node machine with a serial port on it.This node machine will be used to collect logs from your primary machine. Further you need to acquireso-called [[w:Serial cable|null modem cable (a.k.a. serial cable)]] and it must be long enough to connect these two machines.
=== Software setup ===
In your boot loader add the following kernel parameters:
<pre>
console=ttyS0,11500 115200 console=tty0
</pre>
<!--T:10-->{{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.}} <!--T:11-->For example, in GRUB boot loader configuration file <tt>/boot/grub/grub.conf</tt> it looks like this in :
<pre>
title Fedora Core (2.6.16-026test014.1-smp)
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.
<!--T:14-->
It can be usual
<pre>
==== Port setup ====
One more important thing. 115200 in the example above is the rate of emitting port. Recieving Receiving port must also work at the same rate. For example, to tune ttyS0 rate use stty program like this:
<pre>
stty 115200 < /dev/ttyS0
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:
<pre>
# ping -c 1 10.0.2.2
# /sbin/arp -i n 10.0.2.2? (Address HWtype HWaddress Flags Mask Iface10.0.2.2) at ether 00:05:5D:34:11:AF [ether] on eth2 C eth0
</pre>
If the remote netconsole server is outside of local network area, use mac address of default gateway or router on local network area and IP address of remote netconsole server (loging via WAN). Mac address of default gateway or router you can get the same way (ping to gateway/router and see mac address via arp command).
Netconsole documentation is available from <tt>Documentation/networking/netconsole.txt</tt> file under your kernel source directory.
=== Setting up remote side 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
When your kernel prints something on the console, the text will be also captured on this netconsole server.
==== Adding to inittab ====
For automatic care about capturing on console server you can use init respawn feature in this way:
echo "n1:23:respawn:/bin/netcat -u -l -p 6666 >> /var/log/netconsole" >> /etc/inittab
telinit q
==== Adding date/time to messages ====
If you want the log to contain date/time of each line, you can use '''awk''' like this:
netcat -u -l -p6666 | awk '{print strftime("%d %b %Y %H:%M:%S"), $0; fflush(stdout);}' >> /var/log/netconsole
See man strftime for info about how to tailor strftime() argument to your needs.
Note that if you want to add this to /etc/inittab, it should be done like this:
echo "netcat -u -l -p6666 | awk '{print \
strftime("%d %b %Y %H:%M:%S"), \$0; fflush(stdout);}' \
>> /var/log/netconsole" > /usr/local/sbin/netconsole
chmod a+x /usr/local/sbin/netconsole
echo "n1:23:respawn:/usr/local/sbin/netconsole" >> /etc/inittab
telinit q
==== Configuring logrotate ====
For long term capturing you would like to do log rotating some way. With logrotate you can do it by creating config file /etc/logrotate.d/netconsole:
<pre>
/var/log/netconsole {
weekly
rotate 8
missingok
compress
copytruncate
notifempty
# Need to restart logger after log file move
postrotate
# Below line assumes netcat will be restarted by init
killall -TERM netcat > /dev/null 2>&1 || true
}
</pre>
<!--T:53-->
For more details, see man logrotate.
=== Testing netconsole ===
First, check log level of console messages on OpenVZ side by:
cat /proc/sys/kernel/printk
First number should be 7 for testing. You can arrange it by:
sysctl -w kernel.printk="7 4 1 7"
After testing you can restore previous setting the same way.
Load '''netconsole''' module (see above) and on the console server run netcat (nc) command. On OpenVZ side provoke any console message, for example connect any USB hardware or try command:
modprobe tun
If you see any console message on OpenVZ side, you should see message on console server too. If not, something is wrong. When debugging a problem, do not use tcpdump on OpenVZ side — it is not able to show netconsole packets. Instead, use tcpdump on console server. Quite a common source of problems with netconsole are firewalls.
== See also ==
* [[SysRq debugger]]
* [[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]]
