Bootstrap Phase

Video Activity
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Time
21 hours 25 minutes
Difficulty
Intermediate
CEU/CPE
21
Video Transcription
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>> Hello Cybrarys and welcome back to
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the Linux Plus course here at Cybrarys.
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I'm your instructor, Rob Gels,
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and in today's lesson we're going to talk about
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the bootstrap phase of the Linux boot process.
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So upon completion of today's lesson,
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you'll be able to describe the bootstrap phase.
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We're going to talk about the role of
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the BIOS in the bootstrap phase.
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You're going to understand why UEFI/EFI is now used
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to boot in place of the BIOS and we'll also
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understand how PXE works in the bootstrap phase.
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The bootstrap phase is the first phase of Linux boot.
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It's responsible for bringing up
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the hardware, testing the hardware,
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and it also finds the location of
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the bootloader which is necessary
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for us to move into phase two.
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We're going to talk about
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three bootstrap options in this lesson.
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BIOS, UEFI and PXE.
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BIOS, which is the basic input output system,
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is legacy bootstrap was used early on,
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it's still used on older systems,
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and after BIOS happens,
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the system is going to initialize
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the power on self test or POST.
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POST codes are very complicated.
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There's a lot of different POST
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>> codes that you can find,
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>> if POST has errors,
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you're going to hear beeps.
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Maybe sometimes you'll see
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an error message depending upon the motherboard.
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Definitely take a look at bioscentral if you
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need any help determining what those mean.
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But next, the BIOS looks through the list of
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devices for the bootloader
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to move on to that second phase,
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and that's normally referred to as
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the boot or boot order in the BIOS menu,
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and will happen is the BIOS will search the list in
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order looking at the devices
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to try and find bootloader code.
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What it's actually looking for is
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the master boot record, the MBR,
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and that contains the bootloader codes that
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we use to move into phase two.
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Now, BIOS has been deprecated.
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It's not able to keep up with
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a modern hardware and advancements that we see today.
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Can't boot drives larger than 2.1 terabytes.
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It has a limitation on the amount
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of memory addressing access,
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and it can only manage a limited number of devices.
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UEFI,
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Unified Extensible Firmware Interface
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is the replacement for BIOS.
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It can boot those larger drives.
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It can operate in a larger amount of memory space.
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This is configured in Linux with EFI boot manager.
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UEFI looks for storage on
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a device with an EFI system partition ESP.
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Now, ESP is FAT32 formatted.
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Generally you're going to find that at boot EFI,
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and we'll see that later in
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this module as we get into those files.
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But once that ESP is found,
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you can load an OS or you can
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load a bootloader like GRUB,
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and if you want to get into heavy duty detail on UEFI,
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please see the spec.
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Now the preboot execution environment,
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also known as PXE is used to boot server remotely.
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There are two requirements for PXE booting.
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The system has to have a network
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interface card that supports PXE,
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and the system has to have PXE
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enabled as the boot device,
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and what happens then is when you power up the system,
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the NIC tries to obtain an IP address and then it
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transfer files over using TFTP,
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and then the system downloads
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the appropriate boot image from
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the TFTP servers, pxelinux.cfg directory.
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But with that, today we discussed
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the phase one of the Linux
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boot process, the bootstrap phase.
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We talked about BIOS,
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which is the legacy bootstrap process.
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We covered UEFI, which is the modern bootstrap process,
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and we also saw PXE as an option for remote booting.
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Thank you very much for being with me and
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I look forward to seeing you in the next lesson.
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