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In this demonstration, we're going to go over

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how to monitor some of the kernel modules.

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We're going to primarily be focusing on the D message command.

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This will give us a lot of information about what's going on

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beneath the surface at the kernel level

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'cause every kernel module, drivers and other devices

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send messages back and forth to the kernel

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and now we can see you in real time what's happening there.

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Now, a key file that we can use

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to get some information about this kernel

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it's going to be on the proc folder

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under the version directory.

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And here we'll see that it gives us

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the Linux version information,

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as well as the GCC or the GNU compiler collection.

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That's going to be useful for troubleshooting.

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For example, if there's some out-of-date software

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or incompatible software,

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we'll know by getting this information from this file.

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Next, we're going to go ahead and examine

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the kernel message buffer.

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Okay, this is that D message command

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I was speaking about earlier.

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So first we're just going to look at the help command

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and we're just going to read through some of the information

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that's presented to us.

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It talks about the different type of facilities,

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talks about the different type of log levels.

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And we're going to use the warning as an example

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of how to key in on some of that information.

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So we're going to go ahead and get right to it.

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We're going to do the D message command

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and we're going to use the H option.

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So if you see, H is a lot of information

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going back and forth from different drivers,

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other parts of the system, hardware, software,

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anything that pertains to the kernel,

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system resource allocation, errors, starts, stops,

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pretty much anything that you need to know

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relative to information going back and forth to the kernel.

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You're going to get that here.

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Now, for the average system administrator

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this isn't going to be something that you use

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quite often and you might do a lot more research

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to understand exactly what these messages are going for,

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but this is the location that you go to to get it.

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All the way down to the bottom.

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Now, as for a filter, we're going to look for only messages

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that are giving us a warning about something.

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So again, we're going to go to D message

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and do the H for human readable.

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And this L option gives us a level.

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It's going to let us specify the levels

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that we would like to view.

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For example, if we want to view errors or warning.

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So the first one we want to do is a warning.

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So here it keys in on all the information

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that's deemed as a warning that's being sent

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back and forth to the kernel.

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Now, we're going to do this one more time,

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but this time we're going to do it with an error message.

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I only have two error messages thus far,

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but we can see it here.

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So we love to use a pipe operator

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because again it is a powerful filter for us.

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And so we're going to use a D message again

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and we're going to pipe it and we're going to search

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for the USB that we installed earlier.

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Okay now, we look at the screen we can see

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pretty much from start to finish

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anything pretty much kind of relating to USB device drivers,

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core drivers, registration,

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gives us information about the manufacturer, serial number.

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All this information that's being sent

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back and forth to the kernel.

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Now, we're going to do it one more time,

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but this time I'm going to use it with the Bluetooth USB.

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And the most important thing that we're looking for

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is that it's being registered as a new interface driver.

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So I registered and de-registered earlier,

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and so I'll re-register it for this example.

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So we can see all the information here

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and it's clear, and of course, when we use the grip,

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it highlights it, so it's nice, clean, readable for us.

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All right, that was just a quick walkthrough

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on the D message command.

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Pretty much, again, that's the message buffer

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for the kernel.

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And we'll see a lot of key information that we need

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from kernel modules, device drivers,

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and just the order of operations

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that's happening beneath the hood.

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Again, thank you for sticking me with this walkthrough

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and I'll see you in the next lesson.