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Bootloader grammar
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18
README.md
18
README.md
@@ -246,7 +246,7 @@ a binary keymap file I use for belgian azerty.
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The Boot Loader
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---------------
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The next step is to install the bootloader, the program that loads our kernel in
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The next step is to install the bootloader - the program that loads our kernel in
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memory and starts it. For this we use GRUB, one of the most widely used
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bootloaders. It has a ton of features but we are going to keep it very simple.
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Installing it is very simple, we just do this:
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@@ -257,7 +257,7 @@ grub-install --modules=part_msdos \
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/dev/loop0
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```
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The ``--target=i386-pc`` tells grub to use the simple msdos MBR bootloader. This
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is often the default but this can vary from machine to machine so you better
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is often the default, but this can vary from machine to machine so you better
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specify it here. The ``--boot-directory`` options tells grub to install the grub
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files in /boot inside the image instead of the /boot of your current system.
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``--modules=part_msdos`` is a workaround for a bug in Ubuntu's grub. When you
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@@ -266,7 +266,7 @@ think it needs to support msdos partition tables and won't be able to find the
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root partition.
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Now we just have to configure grub and then our system should be able to boot.
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This basicly means telling grub how to load the kernel. This config is located
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This basically means telling grub how to load the kernel. This config is located
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at ``boot/grub/grub.cfg`` (some distro's use ``/boot/grub2``). This file needs
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to be created first, but before we do that, we need to figure something out
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first. If you look at ``/proc/cmdline`` on your own machine you might see
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@@ -278,14 +278,14 @@ BOOT_IMAGE=/boot/vmlinuz-4.4.0-71-generic root=UUID=83066fa6-cf94-4de3-9803-ace8
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These are the arguments passed to your kernel when it's booted. The 'root'
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option tells our kernel which device holds the root filesystem that needs to be
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mounted at '/'. The kernel needs to know this or it won't be able to boot. There
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are different ways of identifying your the root filesystem. Using a UUID is a
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are different ways of identifying your root filesystem. Using a UUID is a
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good way because it is a unique identifier for the filesystem generated when you
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do ``mkfs``. The issue with using this is that the kernel doesn't really
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support it because it depends on the implementation of the filesystem. This
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works on your system because it uses an initramfs. But we can't use it now. We
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works on your system because it uses an initramfs, but we can't use it now. We
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could do ``root=/dev/sda1``, this will probably work but it has some other problems.
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The 'a' in 'sda' is can depend on the order the bios will load the disk and this
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can change when you add a new disk or sometimes the order can change randomly.
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The 'a' in 'sda' depends on the order the bios will load the disk and this
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can change when you add a new disk, or for a variety of other reasons.
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Or when you use a different type of interface/disk it can be something entirely
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different. So we need something more robust. I suggest we use the PARTUUID. It's
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a unique id for the partition (and not the filesystem like UUID) and this is a
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@@ -295,9 +295,9 @@ a GPT thing). We'll find the id like this:
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$ fdisk -l ../image | grep "Disk identifier"
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Disk identifier: 0x4f4abda5
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```
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Then we drop the 0x and append the partition number as two digit hexidecimal. A
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Then we drop the 0x and append the partition number as two digit hexidecimal. An
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MBR only has 4 partitions max so that it's hexidecimal or decimal doesn't really
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matter but that's what the standard says. So the grub.cfg should look like this:
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matter, but that's what the standard says. So the grub.cfg should look like this:
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```
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linux /boot/bzImage quiet init=/bin/sh root=PARTUUID=4f4abda5-01
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boot
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