Troubleshooting Problems

Compiling a kernel is a complex operation, and things can go wrong. Chances are, you will see error messages printed on the screen when something does go wrong. Some of these messages will show up in the /var/log/messages file, which you can look at in any text editor. Other messages may appear in other error logs as well. First thing: Don't panic! Many (if not quite all) problems can be solved with proper research.

Errors During Compile

It's rare that a kernel doesn't compile, but there's always a chance that something slips through the testing process.

A more likely scenario is that the compile crashes before completion when you attempt to experiment with new and untested code. Trying to add support for a newer device to an older kernel can also sometimes result in a compile crash.

It's also possible for you to end up with a tainted kernel. A tainted kernel is one where you have introduced a module that isn't covered by the GPL or similar license. This can happen when you're using hardware that requires a proprietary module (such as Nvidia display adapters). If you compile the kernel with one of these proprietary modules, you will see taint warnings.

Should you run into this situation, you're down to two options: Remove the offending module and wait for a solution from the kernel hackers, or try fixing the error yourself. Most folks might want to take the safer course and wait for a fix, but if you think you might like to help hack the kernel, this is your opportunity. Finding a solution not only solves your problem, it might help millions of users down the road.

If you run into this problem and want to explore it, your first step is to contact the maintainer of the kernel section that did not compile. Go to /usr/src/linux/MAINTAINERS to find the person in charge. Ask if the team is aware of your problem. If necessary, you could post a problem to the appropriate mailing list, but before doing this, look at the If Something Goes Wrong section of the /usr/src/linux/README file.

Runtime Errors, Bootloader Problems, and Kernel Oops

If the kernel compiles, but crashes after you restart your computer, you have runtime errors. Error messages will appear on the screen (you can see them after you've turned off the SUSE boot screen by pressing Esc) or in the /var/log/messages file. Bootloader problems will be displayed on the screen, without a log file. Kernel oops are errors in a running kernel, with the errors written to /var/log/messages.

In these situations, Google is your friend. Chances are quite good that someone else has seen the error message(s) you have, and there are likely documented solutions out there. Head to your favorite search engine and type in the error message with quotes around it. Be aware that Google has a 10-word limit on search terms, so you may need to focus on the keywords in the error message.

Most problems that surface after compiling a new kernel are bootloader-related. If you are running the LILO bootloader and forget to run /sbin/lilo after configuring the new kernel, it will have problems. See the LILO mini-HOWTO at the Linux Documentation Project (http://www.tldp.org/HOWTO/LILO.html) for diagnostic aids and solutions to most LILO problems. The GRUB manual is also online, at http://www.gnu.org/software/grub/manual.