Getting Linux kernel debug information after a kernel crash

Question

Is there a way to get kernel previous debug information after kernel crash occurs.

I am trying to develop a kernel module which basically captures IP packets in the IP layer inside the kernel network stack and after some modification I have to send the same packet back to the NIC for transmission.

During all these processes I'm writing debug information with the help of printk(). But if any thing goes wrong and a kernel failure occurs, we have to restart the system. Is there a way to get my previous debug information, because after rebooting the debug information is not present as I try to get it by dmesg command?

Answer 1

Actually, the /var/log/dmesg file contains the current boot print message log. The /var/log/kern.log file contains your previous boot kernel print message log in Ubuntu. In other Linux flavours it will contain in the /var/log/messages file in Fedora, etc..

Answer 2

Kernel log messages can be viewed in /var/log/dmesg files even after restart of the system.

There will be so many files with dmesg.X, and those files are previous kernel logs. dmesg is the latest file.

See difference between dmesg and /var/log/kern.log