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Absolute OpenBSD, 2nd Edition by Michael W. Lucas

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Altering the Kernel with config(8)

While sysctl lets you tweak the kernel, it won’t let you change values that are hard-coded into the kernel binary. Some of these values are used to initialize kernel data structures, and they can’t be changed once the kernel is running. Others relate to device drivers. Once the kernel has finished probing devices, it won’t go back and reprobe just because you change where a device driver checks for its hardware. To change hard-coded values like these, you must edit the existing kernel file and reboot, allowing the system to set things as you like from initialization. That’s where config(8) comes in.

The config command has two completely separate functions. The first creates a kernel compilation directory from ...

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