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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.

FIXMEHere is a description of a common routine that is necessary to set up a serial console. === 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 thenunfortunately 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 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 === ==== Sending side ====In your boot loader add the following kernel parameters: <pre>console=ttyS0,115200 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:<pre>title Fedora Core (2.6.16-026test014.1-smp) root (hd0,0) kernel /vmlinuz-2.6.16-026test014.1-smp ro root=LABEL=/ console=ttyS0,115200 console=tty debug silencelevel=8 initrd /initrd-2.6.16-026test014.1-smp.img</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. <!--T:14-->It can be usual<pre>cat /dev/ttyS0 > /var/log/serial.log &</pre>or something more sophisticated: syslogd, watchtty etc. ==== Port setup ====One more important thing. 115200 in the example above is the rate of emitting port. 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</pre> Some other serial port parameters, like parity, number of stop bits etc. should also be the same on both sides.

This assumes === Kernel recompilation ===If you have not yet use binary kernel from openvz.org, it already has netconsole module compiled in, so just skip to next section. If you build the kernel yourself, you might need to check if netconsole as a module is compiled. To that effect, change to your kernel source directory and grep your kernel <tt>.config</tt> for NETCONSOLE:<pre># cd /usr/src/openvz/linux-2.6.16# grep NETCONSOLE .config</pre> If you see nothing or into your "# CONFIG_NETCONSOLE is not set" you need to recompile the kernel.

Edit your kernel configuration file, in my case mine was located at /usr/src/openvz/linux-2.6.16edit <tt>.config </tt> with a text editor (<tt>nano .config</tt> or <tt>vi .config</tt>)set . Set netconsole to Y or M (depending on whether you want it as a module or built into the kernel, i installed ; I have compiled it as a module):

save Save the file, then recompile the kernel. :cd /usr/src/openvz/linux-2.6.16 # make bzImage && make modules && make modules_installupdate Update your bootloader for the new updated kernel. in In my case i I use lilo LILO so i I just type lilo at the prompt. Reboot into new kernel. === Setting up OpenVZ side === Next you want your netconsole to send the request to somewhere. Load netconsole module, specifying the remote server parameters:  # modprobe netconsole netconsole=4444@10.0.2.1/eth0,6666@10.0.2.2/00:05:5D:34:11:AF 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 -n 10.0.2.2Address HWtype HWaddress Flags Mask Iface10.0.2.2 ether 00:05:5D:34:11:AF 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 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  socat udp-listen:6666,reuseaddr - 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"

next After testing you want your netconsole to send can restore previous setting the request to somewheresame way.

<pre>modprobe Load '''netconsole netconsole=4444@10''' module (see above) and on the console server run netcat (nc) command.0.2.2/eth0On OpenVZ side provoke any console message,6666@10.0.2.1/00:05:5D:34:11for example connect any USB hardware or try command:AF</pre>

then just setup netcat If you see any console message on OpenVZ side, you should see message on your console server too. If not, something is wrong. When debugging a problem, do not use tcpdump on OpenVZ side — it is not able to listen show netconsole packets. Instead, use tcpdump on port 6666 UDPconsole server. Quite a common source of problems with netconsole are firewalls.

when your openvz == External links ==* [http://kb.odin.com/en/10044 How to configure kdump (kernel performs an OOPS, it will be captured on the netconsole server :crash dump)]