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In this demonstration, we're going to go

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through the Linux boot process.

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It's important to understand the Linux boot process,

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especially when you're a system admin,

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just in case you get a major error called a kernel panic.

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Now, when these errors occur, they require intervention,

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so it's important to understand the components

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and the makeup of the process,

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so you can kind of identify any issues

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or where the problem might lay.

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Now, as sort of a high-level overview,

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what happens when the computer's first turned on

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or restarted?

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The processor checks for the BIOS or the UEFI,

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and the BIOS means it's the Basic Input Output System,

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and the UEFI is the more advanced version of the BIOS,

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which stands for the Unified Extensible Firmware Interface.

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Now, all that really means is the firmware,

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is what's hard coded into the processor,

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so as soon as the computer is booted,

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it has software to run it.

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The next thing that the BIOS needs to do is check

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for any bootable media.

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So, typically, don't look for any external

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or internal storage or peripherals, such as USB thumb drives

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or DVDs, et cetera.

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Once it locates a valid device,

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it starts to boot from that system.

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The next thing it's going to do is look

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for the primary bootloader.

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And that's typically going to be on the master boot record.

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That's if you're using the BIOS,

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or the GUID partition table,

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and that's if you're using the UEFI version,

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and once it pulls this information, then it's going to start

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to load a little bit more information again.

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Again, this is how all a boot strap,

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so, we're starting from a little bit of information,

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a few modules, and we're getting more and more complex.

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After we've located the boot loader,

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we're going to determine which kernel is required, and then,

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we're going to locate all the information for the kernel.

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And then we're also going to upload something

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called a initrd image, which stands for initial Ram disc.

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And what this does is pretty much,

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creates a temporary file system

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to start loading the other kernel modules

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as well as the necessary drivers.

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And once the kernel's fully up and running,

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next thing we're going to do is mount the root partition,

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then, we're going to get started using the operating system.

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So just a note, some of the key information, again,

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the most important thing is realizing that the BIOS

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or the UEFI must be initialized before anything can happen.

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And we also have to have viable bootable media,

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and then we actually have to load the primary boot loader

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from a MBR.

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And after the boot loader is complete,

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remember, it's going to transfer control over to the kernel.

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Now, on newer systems, most people are going to go

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with the UEFI and some,

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some of the biggest reasons is because also the GPT,

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the GUID Partition Table has a lot more advantages

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over the legacy, MBR,

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because it has a larger maximum storage space

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for the partitions,

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and it also stores the boot data

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in multiple locations for redundancy purposes.

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So now you're not running into a issue where,

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for example, if you using the BIOS

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in the primaries and the first sector gets corrupted,

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and now you can no longer load the system.

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And one of the last things that's ran is the systemd

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and what that does is it just mounts the file system based

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off that configuration file that we configured earlier,

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the f staff file, and then begins the process

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of starting all the services that we're going to need

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to run the operating system.

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Now, note on a lot of systems today,

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especially when everything's becoming more connected

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and complex, a lot of organizations today,

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they're booting a lot of the operating systems from a NFS,

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so a network file share.

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We're going to actually go through,

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and configure how to set up a network file share

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for our server to create a bootable image

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to load on multiple machines.

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So let's get started with that.

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Okay, so, the first thing we're going to have

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to do is identify the kernel that we're currently using,

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and that's going to be the uname command to r option.

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Okay, so we see that version,

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now, probably go ahead and make an initial Ram disk.

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So that command is going to be sudo, make initial Ram disk.

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We use the verbose option to see everything

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as it's being processed.

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We're going to put it under the boot directory,

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init, rd,

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so this is going to be the name.

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So this portion of the command is just specifying the name.

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Now, when we have this dollar character,

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it's, lets us use a variable,

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and it's going to be the variable that's returned

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after we execute this command.

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So dot image, so this is going to be the name

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of the actual file.

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So it's going to be in the boot folder

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and it's going to be init rd

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with a version dot kernel dot image.

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And then, the last specification we must have,

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is the actual kernel that we're going to be using.

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And again, we can use this variable, uname,

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and then we need our r option,

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put in our password, and we're going to run it.

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Okay, we see we have that complete there.

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Now let's just make sure that that actually was created.

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Want to list it out.

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We go to our booth folder,

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and we look at it where it says the date of June 13th.

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About halfway down the file,

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we'll see that new file was created.

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So the image we just created,

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it refers to the root file system,

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that's going to be temporary loaded

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into the memory upon system boot.

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Now, we're going to do the same thing,

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but we're going to create one with a network file share module.

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When they initially boot,

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the temporary root system will be coming

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from a external device across the network.

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So going back to that same command,

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so this is just going to add to the option

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with network file share V four,

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and we're just going to slightly change the name to,

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we're going to put network file share,

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NFS just for clarification,

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okay?

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All right now, let's just verify this really quick.

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We're going to go back to this boot folder,

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and we see they're right next to each other,

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so that's easy for us to identify.

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Let's make this a little readable here,

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and do the human readable, so we can get the bytes for this.

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Now, if you look, you'll see that the network file share,

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is slightly larger than the initial kernel,

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and that lets us know that it introduced a new module

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into the initial Ram disc.

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Okay, we just walked through how

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to create an initial Ram disc image,

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and also one with the network file share option,

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and I'll see you in the next lesson.