Fedora 17 random reboots: where to begin troubleshooting?

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dmesg might be a place to find a hint as well. You can find the log in /var/log/dmesg or just run dmesg and pipe through less or more.

Do you have sysstat running on the machine? If not, that might help you determine if it's CPU consumption related, memory related, etc. Sysstat will check system resources every 10 minutes and print them into daily log files @ /var/log/sa/sa## ( ## for the numerical value for the current day ). It will keep 7 days by default. You can then use the 'sar' command to parse through the log files and print information you request. It's a helpful tool when initiating an investigation such as this. It's also customizable.

Assuming there's an actual panic that's causing this, the way I've always captured it was through a serial console. Null-modem connection to another computer and capture it to a file.

Looks like http://fedoraproject.org/wiki/Howtousekdumptodebugkernel_crashes might be another way.

you can still try to use netconsole. Which will send kernel message over the network:

#Client
nc -l -u 6666

#Server - will not preserve restart
insmod netconsole netconsole=4444@192.168.178.1/eth0,66..

#Server - will be configured after restart
echo 'options netconsole netconsole=4444@192.168.178.1/eth0,6666@192.168.178.59/e0:49:75:c3:0b:ff' >> /etc/modprobe.d/netconsole.conf

192.168.178.1 = Server IP

192.168.178.59 = Client IP

http://www.kernel.org/doc/Documentation/networking/netconsole.txt