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Squid: The Definitive Guide by Duane Wessels

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Chapter 16. Debugging and Troubleshooting

No matter how hard the Squid developers try to be perfect, you may encounter some problems with Squid. These problems range from misbehaving clients and servers to fatal bugs in the Squid code. In this chapter, I’ll talk about various ways you can debug these problems.

Some Squid problems may require you to turn on debugging. In most cases, you’ll want to increase the debugging levels for specific parts of the code. I’ll describe how to find out what those debugging sections are and how to change the settings. Also, I’ll talk about the importance of providing detailed debugging when reporting bugs.

Finally, you may experience fatal bugs in the Squid code. These can result in segmentation violations, aborts, assertions, and core dumps. The core dump is a useful debugging aid. With a debugger, such as gdb, you can generate a process stack trace and send it to the developers for assistance.

If you suspect you have a Squid bug, but aren’t sure, check with the squid-users mailing list or one of the other resources described in Section 1.6.

Some Common Problems

Before discussing debugging in general, I’ll mention a few specific problems that commonly arise.

“Failed to make swap directory”

Failed to make swap directory /var/spool/cache: (13) Permission denied

This happens when you run squid -z, and the Squid user ID doesn’t have write permission to the /var/spool directory. Remember that if you start Squid as root and don’t add a cache_effective_user ...

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