sysfs File System (Demo)
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Video Transcription
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>> Hey Cybrarians, welcome back to
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the Linux Plus course here at Cybrary.
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I'm your instructor Rob Goelz and in today's lesson,
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we are going to be talking about the sysfs file system.
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Upon completion of today's lesson,
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you're going to be able to understand
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the purpose of this sysfs file system.
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We're going to explain the information that's
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held in the sys directory and then we're
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going to review the contents of
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the sys directories to find information.
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The sysfs file system is really
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just another virtual directory or
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pseudo file system similar to block,
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and in this case,
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the virtual directory is mounted at /sys,
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and that's used to provide
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>> user space with properties and
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>> statistics from hardware devices and file systems.
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Kernel modules detect any device on boot and it creates
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a subdirectory in that sys
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virtual directory or pseudo file system,
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and that just contains the device information.
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Sys has a lot of directories,
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but an abridged listing here
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would be things like /sys/block,
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which is going to contain information on block devices,
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/sys/bus is going to contain
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any statistics about system buses,
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as well as entries and drivers for
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devices that are found on the bus.
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The /sys/devices directory holds
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a hierarchical device presentation,
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so the actual devices that we find in
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/sys/bus devices are going
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to be semi-linked into /sys/devices.
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/sys/fs is where you find information about
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mounted filesystems or devices
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that are using file systems,
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and then finally, /sys/kernel
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holds kernel status information.
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Let's look closer at this with some demo time.
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Here we are back in Ubuntu,
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and let's first of all just get
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a basic directory listing of sys.
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In here what we can do is we can see
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a bunch of different information like I said,
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we can see information about block, bus,
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devices, fs, and kernel.
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Let's take a look at the bus directory first.
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Let's do an ls on /sys/bus.
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Inside of here we can see all of
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the different devices that exist on the system.
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Let's just pick one to take a look at.
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Let's look at the folder
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for the discovery bus so we could do
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an ls-al
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on /sys/bus/scst.
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Then we can also see that there's a folder
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for devices and drivers on this scst bus.
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Let's look at the devices folder.
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We'll do an ls-al on sys/bus/scst/devices,
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and there we go.
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We see that these are actually
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all siblings to the devices folder.
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This.. /../../ Tells us
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that it's going up three directories two devices.
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If we just go up 1, 2,
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3, this is where these are actually all stored.
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We can see in here
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the devices and they'll be pointed to different PCI.
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So we see PCI 000,
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0000. Here we go right here.
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If we do an ls-al on that,
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we can see all those scst devices.
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Likewise, if we do an ls-al on,
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let's say /sys/block/sda,
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we can see that this is also
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similarly back into devices directory.
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It's semi-linked into the PCI yada yada yada,
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which is how this is
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the actual bus that the drive is using.
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Really, since it's
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just a way for the kernel to organize data,
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statistics and properties on devices,
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and then other applications can make use
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of this data in the Linux operating system.
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But with that, we've reached the end of this lesson.
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In this lesson we covered
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the purpose of the sys file system,
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we talked about the information that's
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held in the sys file system,
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and then we got to take a look at the content
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of some of the sys directories.
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Thanks so much for being here and I look
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forward to seeing you in the next lesson.
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