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Remote console setup

2,638 bytes added, 02:57, 27 November 2018
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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>
<!--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.}}
 
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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.
<!--T:14-->
It can be usual
<pre>
Save the file, then recompile the kernel:
<pre> # make bzImage && make modules && make modules_install</pre>
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:
<pre> # modprobe netconsole netconsole=4444@10.0.2.1/eth0,6666@10.0.2.2/00:05:5D:34:11:AF</pre>
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
Setup netcat on your console server to listen on port 6666 UDP:or
<pre>netcat socat udp-u listen:6666,reuseaddr -l -p6666</pre>
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:
<pre> echo "n1:23:respawn:/bin/netcat -u -l -p 6666 >> /var/log/netconsole" >> /etc/inittab telinit q<==== Adding date/pretime 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:
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>
=== Testing netconsole === <!--T:53-->For more details, see man logrotate.
=== Testing netconsole ===First , check log level of console messages on OpenVZ side by:
<pre> cat /proc/sys/kernel/printk</pre>
First number should be 7 for testing. You can arrange it by:
<pre> sysctl -w kernel.printk="7 4 1 7"</pre> After testing you can restore previous setting the same way.
After testing you can repair previous setting Load '''netconsole''' module (see above) and on the same wayconsole server run netcat (nc) command.On OpenVZ side provoke any console message, for example connect any USB hardware or try command:
Load netconsole module (see above) and on console server do netcat command. On OpenVZ side provocate any console message, f.e. connect any USB hardware or try command: modprobe tun
<pre>modprobe tun</pre>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.
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 common the 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]]
Retrieved from "https://wiki.openvz.org/Special:MobileDiff/3520...23049"

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