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Hey guys and welcome back. So in the previous nugget we had talked about the boot process

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with respect to our Linux system and we happened to mention the concept of boot loaders. Now

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I did say we had two different boot loaders, there actually are more we'll get to look

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at some more a little bit later on but the main ones we want to focus in on are Grubb

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and then after this nugget right here we'll talk about Grubb 2 which was the replacement

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but for now let's begin with Grubb itself. So Grubb like I say otherwise known as legacy Grubb

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since it has been ultimately replaced this stands for the grand unified bootloader GRUB.

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Now the Grubb bootloader ultimately replaced older systems such as Lilo which we will talk

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about very very shortly but eventually as good as Grubb was and as much of an improvement over

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Lilo that it was it did eventually run into some limitations. So as such you really are not going

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to see the original Grubb in use very much anymore and the reality is we just have to understand

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this information for both historical purposes and really for the purposes of the examination

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because this is still a subject whereby you may receive questions on. Now with respect to legacy

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Grubb what we want to understand are some key components the first thing which I want to talk

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to you about is the Grubb legacy configuration file. Now this is going to be at a particular location

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and that location is going to be in the boot directory and then within this the Grubb directory

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and then the file will be called grubb.con so really try to remember the name of this file here.

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Now like I say because we have the updated version of Grubb Grubb too now it really isn't quite so

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easy to be able to get your hands on an old configuration file but for the purposes of letting

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you see what one may look like I have created my own right here. So this is not a complete

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configuration file most of the information has actually been removed but what we actually want

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to know for the purposes of the examination I have included. So when we look at this configuration file

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we have some particular settings we can see these on the left here things like the default setting

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or the timeout setting or the splash menu or the hidden menu so on so forth. We want to understand

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what these settings actually are and what they're doing. Now with respect to the very first setting

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the default setting let's talk about that for a moment. So let me show you what I mean when I

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say this. All I'll do here is search for Grubb menu and you can kind of get an idea what I'm talking

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about here. So we can see this little menu here okay now the one at the very top here this is the

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operating system with the particular kernel we're going to be loading into. Now what we're looking

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at here are all these different titles okay. Now if you don't actually change the title i.e. what we

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have selected to maybe be another option say for example this one here and you can do this by using

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your arrow keys to arrow down to the option you want to choose. If a particular title is not

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selected before a particular timeout value has exhausted itself the one that is going to be

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selected is the one at the very top. Now this is going to be assigned a value of zero whereas the

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second title the one below that would be assigned the value one. So if we happen to change this value

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here to maybe be the value one if we go back and we look at the menu option here the one which would

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load if we do not select anything by the time the timer exhaust itself will be option number one.

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So the very first one would be zero the next one would be one the next one would be two so one so

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four so if we set the value to one as the default that means if we don't select anything it's going

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to be this one here that is going to automatically load you see that that will be our default option

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and like i say to start off with the default is going to be zero which will be the very top one

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right here so we can toggle that value. Now we just happen to mention the concept of a timeout

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whenever a timer runs out we will select by default a particular option. Now the value

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of how long we want to wait can be denoted right here so what we have right here and my little

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example here is the value of five this denotes five seconds that means that once we begin to load

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up we're going to have five seconds to choose a particular option and if we do not choose anything

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by default we will choose value number one so all this timeout here is ultimately a countdown

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and it's a countdown in seconds so you could if you so choose extend this to be much longer say

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for example 30 seconds or you could put it down to one second if you want this is ultimately up to

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you so now we move to our next option the splash menu all this is is the graphic displayed when

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you're going to see that grub but menu we just saw there now what we're looking at right here

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happens to be a particular image and it's going to require this particular extension xpm.gz

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with xpm actually denoting the graphic format in gz you may recall just means it is a compressed

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image now we also have this option here for a hidden menu one thing to note here is that this

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menu doesn't actually have a correlating value you see the way before we had this equal sign here

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and equals here and equals here to give each option a particular value in the case of default the

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value is one in the case of timeout the value is five so on so forth with hidden menu we do not have

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any equals sign we do not have a value to correlate simply puts if this option here happens to be

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present within the configuration file which in my case right here it is the grub menu is not going

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to be displayed instead the only thing you're going to see is that countdown timer so that means

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that if you happen to press a key on the keyboard before the timeout actually ends then you will

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actually see the graphic menu but otherwise it's going to be hidden away from view now the next thing

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we want to talk about is this portion right here and this really is i would say more of an important

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portion to focus in on because well the top part is still quite important it's ultimately window

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dressing so to speak but is this part here is definitely not the title okay so what is this

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part right here so the title is basically what is going to be the name that is going to be displayed

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in the grub menu when the actual boot process happens now typically you want to display the name

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of the distribution as well as the kernel version for that distribution so if we happen to go again

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and look at the example from the boot menu we can see here we have ubuntu on the left here

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which is the distro and we can see the linux kernel version that it's going to be using in this case

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here you kind of get the drift we want to be pretty descriptive about what it is that is actually going

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to be loaded up so really what we see here is ubuntu with linux 380-35 generic with this configuration

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file what you would see in the menu is sent os and then 2717 now it's important to note that you do

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not have to specify this particular format it just is kind of deemed good practice because it is

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pretty descriptive now the next thing we want to talk about is this setting right here the root

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setting okay now what this is going to do this is going to point to the device that actually has

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the boot files so that would mean the kernel file and the init rd file now you might be noticing

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that below these are two settings we're going to see here this is exactly what we're talking about

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but with respect to this part right here all we are doing is trying to locate where about on the

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disk we can find such things now one thing here which is worth a note we see this value here hd0

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0 okay now the thing to note straight away is that with respect to grub we have no distinction

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between ide devices and sata devices so you may recall from the lpik one we saw things such as

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maybe hd a which would be our ide and we would also have sda which would be our sata disks notice

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here we're actually making no such distinction we actually can't tell if this is ide or sata it's

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just hd0 0 now the part which is pretty confusing and this is what actually is going to be a little

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bit different so when we see hd0 0 what this is actually pointing to is sda1 or if you wish hda1

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but the point i'm making here is that this value here denotes the very first disk and this value

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here denotes the very first partition so what i'm saying here is is that if we see the value 0 it

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actually means the first partition whereas we typically would be looking at something like say

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sda1 and the value 1 would mean the first partition not in this case here what we're seeing here is

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that the value 0 actually correlates to the first partition as well as the first disk so if we happen

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to have the value hd and then 0 1 for example well we would know this would be on the first disk so

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that would be something like say sda a being the first disk and the one would actually be the second

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partition which should be number two right here so this part sometimes catches people out because

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we are starting from the zero value and not the value one so ultimately this is where we're going

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to be able to find our kernel image and our initrd image i.e. what disk in what partition

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but the name of the kernel image we want to be using is going to be specified at this part here

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using the kernel keyword so the actual kernel we would be using would be in the boot directory

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and it would be called this right here in my case vmlinnus2717 our all would mean read only and then

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what we have to do in this part really is crucial we have to specify where we're going to mount the

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root file system now these two values we're going to see afterwards these actually relate to red hat

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based systems what rhgb actually stands for is the red hat graphical boot this is just simply a

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graphical user interface that is going to boot with most of the information hidden and this is

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what we're doing when we specify this quiet option we want to hide the majority of the boot messages

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now that is the kernel location the initrd again going to be within the boot directory on the first

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disk of the first partition of the hard drive and the name of the initrd image is going to be in this

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case here initrd2717 image now one thing we want to be aware of is that our initrd is going to

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reference a particular kernel number which we can see here and we absolutely want to make sure that

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that number matches what the kernel is we have here if we have a mismatch here then we're going to be

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in trouble we're not going to be able to get things to work correctly so that really is us for our

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little introduction into grub legacy like I say we are kind of limited as to what we can actually do

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because this is a legacy based system but what we have learned here is actually quite transferable

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to what we're going to see with respect to grub2 and that is what we're going to be looking at in

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the very next nuggets I hope this has been informative for you I'd like to thank you for viewing