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- [Instructor] Let me point you to

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a few more

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Linux source code directories

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that I think are worth spending a couple minutes looking at.

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So include,

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so remember when you're building the kernel,

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it does not use,

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include files, header files

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from the ordinary user space directory.

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It's only using include files

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from the kernel source directory.

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So that's underneath the include subdirectory.

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But by the way, when you build a kernel,

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you build include files that user space will need

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so that when Linux systems get built,

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some of the header files come from the kernel

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because user space sometimes needs to know

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what data structures look like.

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So user space won't be using kernel include files directly.

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Those kernel include files that get built,

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you know, get copied into the user space plus part

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as part of building a Linux distro.

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Right, so some of those files in the user include directory,

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like the standard C library, which is

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where the system call user space component is.

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Those right, need to correspond to your kernel.

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Another directory, I think is interesting,

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is fs, which stands for file systems.

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And underneath there you can find code for proc and sysfs

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and for the disk file systems, ext four,

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btrfs, xfs, so forth.

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Network file system stuff,

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and non-native Linux file systems,

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compatible file systems like for NTFS or FAT.

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Oh, I think that's kind of interesting.

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Another directory I find interesting is Arch,

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where the support for the different computer architectures

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for Linux is kept, right?

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So Linux runs on lots of different kinds

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of computer architectures.

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It's actually quite portable operating system.

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Pretty amazing.

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So Linux runs on computers with 32 bit or 64 bit,

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single or multiprocessor,

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plus a bunch of different architectures.

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So the architecture dependent code

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is divided up in those subdirectories.

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And then, one more directory you might find interesting

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is the security directory.

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And in there is the short little name security.c.

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That file is pretty interesting.

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That's the fundamental hooks that SELinux

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and AppArmor and other sort of security systems use.

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This is where the filters are

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so that when a process makes a system call

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SELinux or AppArmor can have hooks

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that get invoked to check things

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to see if it's allowed or not.

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All right, so perusing security.c might be interesting.

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I think it is.