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- [Instructor] The Linux kernel is modular.

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You can have Loadable Kernel Modules, LKMs.

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An LKM is an object file.

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It's got a .ko suffix,

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and then compressed ones have a .zst after that,

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so, .ko.zst.

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So these have code,

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and that code's going to run in kernel space.

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So this gets dynamically linked into the kernel,

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and now there's more functions in the kernel.

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Usually, these are written in C,

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and they're compiled for a particular kernel version.

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So you have copies of the modules

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for each kernel you have installed.

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Kernel modules are not binary compatible

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with different kernels.

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That's important because data structures

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could be different, for example,

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in different kernel versions.

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it's really nice that the kernel is modular.

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That means that the kernel file itself

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can be relatively small,

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and then you can just add functionality to the kernel

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after you boot.

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And that's common.

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There are lots of modules probably loaded in your kernel.

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And it also means that you don't have to build your kernel,

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say, with all possible ethernet drivers.

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You just add the ones that you need after it's booted.

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It makes for a much less memory usage, for example, right?

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And you can do a live update, potentially.

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Generally, it's not such a good idea

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to ever remove a module, because it's kind of risky,

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but, certainly, during development,

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if you're writing kernel code, and it could be a module,

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then you can load your code, give it a try,

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"Oh, that didn't work,"

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make changes, unload the previous version,

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load the new version.

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It's really handy.