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Hey guys and welcome back to another skill in the L pick 2 course.

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So what we're going to be focusing on in this skill right here is around the kernel.

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So let's begin by discussing what the kernel actually is then shall we?

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Now the first thing to note about the kernel is that it is a modular construct,

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i.e. it is not one large entity that does absolutely everything.

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Instead you can much more accurately conceptualize it as a core program and this core program

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can actually be extended to do additional things via the use of modules.

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Hence why it is referred to as modular. These modules can ultimately expand the kernel's

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capabilities. Now the concept of modules is certainly something we will talk about within

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this skill. We'll learn how we can actually load modules as well as remove particular modules we

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do not need as well as listing the modules we do actually have operational. So what exactly

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are the types of tasks that the kernel will handle then? Well it is involved in some very

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important tasks, things such as managing hard drives for your storage or perhaps maybe your

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network card for network connectivity as well as dealing with USB devices and other removable

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storage. So let's take the example of a USB stick. When you plug that USB into the system,

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of course you want that USB to be operational. Now in order for this to happen, the kernel is going

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to load particular modules relating to the USB and if you happen to remove the USB, well the kernel

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no longer needs those modules so those modules will subsequently be removed. Of course the

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alternative to this would be you could have a very large and bloated kernel which would ultimately

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have all possible modules loaded all of the time but clearly this is inefficient so this is not how

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we can expect the modern kernel to operate. Instead we're going to be using that modular process by

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loading modules as they are needed and removing them as they are no longer needed. Now one thing I

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want to talk to you about first is related to the kernel versioning number. So back in the olden

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days the way this was actually numbered would be something like this okay so it would be one, four,

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maybe three and twelve. This is how you could expect to see your kernel version. Now this might

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just seem like a random spattering of numbers but there actually was a very particular format going

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on here so let me show you what this is just draw these out once again. So the very first number would

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actually denote the version number itself so this would be version one of the kernel. The second

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number would be denoted as the major revision. The third number would denote releases where we had

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a minor revision to the kernel and the last number right here this would be for patch management i.e

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if we had some type of security patch that we had to fix we could ultimately update the kernel

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with the latest patch and we would denote that in this part right here. So we have the version,

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the major revision, the minor revision as well as the patch number. Now eventually we worked up to

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kernel 2.6 and then we had some minor releases after that like you say 2.6, 1, 2.6, 2 you get the

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drift. Now before we actually reached version 2.6 there was some information baked into the numbering

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with respect to odd numbers and even numbers what exactly am I talking about? Well if we had a

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version before version 2.6 such as maybe 1, 5, 4 perhaps this number right here i.e the second

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number which would be the major revision if that number happened to be an odd number which is right

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here 5 is an odd number this would let you know that this was a development release i.e this was

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not fully tested it may not be stable you can install it to get the latest features available

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but be aware that it may actually cause your system problems and may not be quite as reliable.

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Now when this was sufficiently tested and became stable we could then have something like say 1,

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6, 4, 6 would be an even number and because we saw an even number in the major revision we would

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know this was a stable release so we should not expect any type of wonky features or major bugs

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so at a glance if i happen to show you 1, 2, 1 you would know that 2 is an even number therefore

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this would be a stable release whereas if i happen to show you something like say 1, 7, 4, 7 happens

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to be an odd number this would be a development release now like i say this continued on all the

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way until we hit 2.6 now version 2.6 was a kind of a milestone for the linux kernel it was very

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very successful and it happened to be used for a very very long time and it was actually from this

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point that the numbering system happened to change so what exactly were the major changes well now

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we would have the version which would be 2 it would be number 6 and instead the last number would

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be the revision number and every release here would be a stable release so instead the format would

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be you would see 2, 6, 1 and then 2, 6, 2 then 3 then 4 then 5 on and on and on and on all the way up

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to 2.6.39 with every single release being stable but as you can imagine this was eventually and

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gradually becoming out of hand and the maintainers of the kernel thought you know what we can't actually

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just keep claiming higher and higher what are we going to do end up with version 283 or maybe 2831

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you can't get the drift so it was decided that the numbering had to be updated yet again so now

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we flash forward and we actually get to version 3 and we have a similar format to what we saw before

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let's say 3.0.x this is the version once again this would be the major revision and the x would

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denote any kind of minor revisions and patches so if we happen to have some type of stability patch

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that had to be pushed out it would be denoted as this last number right here once again though

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crucially is that all releases were aimed to be stable there were no more attempts to push out

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development branches that practice instead was ultimately deprecated so if you happen to see a

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version i don't know maybe 3 4 2 it's version 3 major revision 4 and we have our second minor

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revision or stability patch and this has continued on since so in 2005 we actually had the release of

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version 4 again following the same format version the major release or major revision should i say

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and the patch and then in 2019 we then had our first version of version 5 again following the

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same format version major release and our patches so when you happen to be looking at these kernel

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images you can expect to see this particular format like i say in the older versions you may see

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four numbers before version 2.6 you may be able to infer a development release as opposed to a

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stable release depending on if we are using odd numbers or even numbers and then since version

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3 we are following this simple format so if i go to my terminal and i happen to type the command

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uname-r this is going to show me my kernel number so we can see here i'm using version 5 it is major

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revision 13 and the minor release or the patch is 028 generic and if i happen to go into my boot

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directory so forward slash boot and i do an ls in fact let me long list this to make it a little

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bit more readable you will notice is that the initrd image has a sim link which corresponds to that

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actual kernel number you see that here 5 13 028 generic that is exactly the kernel which i am

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using now the initrd we actually discussed this in lpik 1 ultimately it's like a very very small

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kernel that allows you to access the hard disk where the main kernel actually resides now what

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i also want to show you briefly is if we go into the lib folder and then the modules folder i do an

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ls you're actually going to see here a directory for each kernel we have on the system so i have

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this one right here 5 13 028 which is what i'm using but i also have 5 11 0 27 so if i happen to go

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in to 5 13 and do an ls these are all the modules and dependencies needed for the operation of my

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particular kernel that i'm using see that the name here corresponds to the folder here and within we

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have the modules so that is us for our brief introduction to the kernel we still have a lot

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of information to get to so i hope this has been informative for you and i'd like to thank you for