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- [Instructor] Let's talk a little bit

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about the sys file system, which is mounted on /sys.

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So this should happen automatically at boot time,

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so you could change directory at /sys,

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you should see lots of stuff.

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Originally, sysfs was for showing

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how hardware is connected on your system,

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hardware with buses and connections is a tree structure,

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just like a directory,

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so you could walk the directory structure

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and walk the hardware information.

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It still has that and lots more.

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In fact, underneath sys you should probably find

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tens of thousands of files and directories.

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We're not going to talk about all of them.

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In fact, it's difficult to talk

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in any kind of breadth about the sys file system,

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but we're going to hit some high points for you.

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A couple of my favorite things underneath sys actually

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are the debug file system and the tracing information.

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When I'm working on a device driver or something like that,

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it's really nice to find out what's going on in the kernel,

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for example, tracing all the functions being called

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can be helpful.

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Another place in sys that I find valuable

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is information about loadable kernel modules.

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If you go into sys module, you'll see a subdirectory

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for every dynamic loadable kernel module.

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It's actually whether they were dynamically loaded,

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or they were linked in their kernel image,

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they're all there.

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So that's more comprehensive

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than listing just dynamically loaded modules.

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As I mentioned, there's lots of hardware information,

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there's lots of device information underneath sys.

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There's a subdirectory /sys/dev that shows you information

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about all the block and character device files

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and block device information underneath /sys/block.

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Underneath the /sys/class are classes

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or types of devices, like /sys/class/net

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to find out about your network devices, lots of stuff.

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You can spend quite a bit of time

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just looking around at stuff.

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It can be interesting. Yeah, have a look.

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Plus, we'll do a challenge.