How do I get the correct .config file for compiling the Linux kernel source specific to my hardware?

Question

I tried using make defconfig to compile the kernel, but as expected, it failed to boot. I was wondering what .config file do kernel vendors like Canonical for Ubuntu use, that the kernel is able to boot right out-of-the-box. Of course, I am still a beginner and configuring the various parameters, is a little out of my league currently.

Specifically,I am looking to load a basic "hello, world!" module to my running kernel 2.6.32.41. For that, I would need to compile kernels source against the same .config file that was used for the running kernel.

Answer 1

If your running kernel was compiled with the CONFIG_IKCONFIG_PROC option, you can get the config in /proc/config.gz:

$ zcat /proc/config.gz >my_config

Copy my_config into your kernel build directory as .config and run make config to be prompted for configuration options that are absent from your config file (this will only happen if you are using a kernel source that is newer than your running kernel). You should then be able to compile a new kernel with the same features as your current one.

Distros typically use their own kernel configuration, where most of the drivers are compiled as modules to be dynamically loaded when the corresponding hardware is requested. Also the kernel needs to be booted with relevant boot options (like the one specifying the root filesystem). Your defconfig kernel probably failed to boot because of that.

Answer 2

I don't know about getting the one that's "correct for your hardware", but you can use the config that Ubuntu gives you by looking in /boot/ for a file starting with the name config. There may be more than one, in which case use the command uname -r to tell which kernel you're currently running, and then you can use the appropriate config.