Chapter 13. Reading BIND Debugging Output
"O Tiger-lily!" said Alice, addressing herself to one that was waving gracefully about in the wind, "I wish you could talk!"
Turning On Debugging
Reading Debugging Output
The Resolver Search Algorithm and Negative Caching (BIND 8)
The Resolver Search Algorithm and Negative Caching (BIND 9)
"We can talk," said the Tiger-lily, "when there's anybody worth talking to."
One of the tools in your troubleshooting toolchest is the name server's debugging output. As long as your name server has been compiled with DEBUG defined, you can get query-by-query reports of its internal operation. The messages you get are often quite cryptic; they were meant for someone who has the source code to follow. We'll explain some of the debugging output in this chapter. Our goal is to cover just enough for you to follow what the name server is doing; we aren't trying to supply an exhaustive compilation of debugging messages.
As you read through the explanations here, think back to material covered in earlier chapters. Seeing this information again, in another context, should help you understand more fully how a name server works.
13.1. Debugging LevelsThe amount of information the name server provides depends on the debugging level. The lower the debugging level, the less information you get. Higher debugging levels give you more information, but they also fill up your disk faster. After you've read a lot of debugging output, you'll develop a feel for how much information you'll need to solve any particular problem. Of course, if you can easily recreate the problem, you can start at level 1 and increase the debugging level until you have enough information. For the most basic problem -- why a name can't be looked up -- level 1 will often suffice, so you should start there.
13.1.1. What Information Is at Each Level?Here's a list of the information that each debugging level produces for BIND 8 and BIND 9 name servers. The debugging information is cumulative; for example, level 2 includes all of level 1's debugging information. The data is divided into the following basic areas: starting up, updating the database, processing queries, and maintaining zones. We won't cover updating the name server's internal database -- problems almost always occur elsewhere. However, what the name server adds or deletes from its internal database can be a problem, as you'll see in Chapter 14, "Troubleshooting DNS and BIND".
BIND 8 and 9 have a whopping 99 debug levels, but most of the debugging messages are logged at just a few of those levels. We'll look at those now.
184.108.40.206. BIND 8 debugging levels
220.127.116.11. BIND 9 debugging levels
Keep in mind that this is debugging information -- it was used by the authors of BIND to debug the code, so it is not as readable as you might like. You can use it to figure out why the name server isn't doing what you think it should be or just to learn how the name server operates -- but don't expect nicely designed, carefully formatted output.
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