Setting up netconsole
Assume we have two computers on the same network.
The machine with a problem (the debugee):
IP address: 192.168.1.1
And a second machine (the debugger):
IP address: 192.168.1.2 MAC address of eth0: 00:11:22:33:44:55
The debugger
On a different machine than the one you are seeing the problem, you need to run nc -l -u 6666
This will listen on udp port 6666 for any messages.
The debugee
On the machine that you're trying to debug a problem, run (as root) modprobe netconsole netconsole=4444@192.168.1.1/eth0,6666@192.168.1.2/00:11:22:33:44:55
If you replace the IP/MAC addresses with those relevant to your machines/network in the command above, you should see messages appearing on the debugging machine.
For more information on netconsole, see http://www.mjmwired.net/kernel/Documentation/networking/netconsole.txt
logging levels
You may want to raise the level of printk's that go to the console.
To do this when logged in:
dmesg -n 8
netconsole at boot
Raise the level of console by default logging by adding this line to /etc/sysctl.conf:
kernel.printk = 8 4 1 7
Add your network info to modprobes of netconsole:
$ cat /etc/modprobe.d/netconsole.conf options netconsole netconsole=4444@192.168.1.1/eth0,6666@192.168.1.2/00:11:22:33:44:55
Firewall config
Your netconsole server needs to accept udp on port 6666. This may require a change to your iptables rules.
Comment: does default Fedora rules allow local network connections?