GRUB is confusing

I agree, Grub is horrendous and one of the most complex systems in linux. Grub2 is even worse, and searching the web for help is difficult as the two are named interchangeably, despite being hugely different in design.

Random files spread over the filesystem. Some you edit, some are done automatically, some are done by kernel upgrades, some you need to run yet more commands for them to work - and it all differs from distro to distro. The sooner more distros move away from this, the better.

Since you use UEFI, you don’t have to use GRUB. It basically consists 90% of cruft left over that was needed for BIOS boot, and has a lot of moving parts and bad design (such as a single config file which has to be shared between OSes, which is so complex it needs a generator for it).

Try systemd-boot, it’s lightweight and well designed.

Anyway, looks like the target parameter is default now, the “esp” in the arch command is supposed to be substituted for the ESP path, for example /efi, so the only difference is bootloader-id. Which looks like that’s the label that show up in your UEFI setup for the boot entry.

I just copy paste commands from Arch wiki and it just magically works without me knowing anything about it.

Join the club.

https://wiki.archlinux.org/title/EFI_system_partition#Typical_mount_points
(Efi System Partition)

GRUB gets installed on your harddisk in your root partition, it's configuration file on the boot partition and finally into your boot sector if I'm correct. UEFI is a standard for your firmware located outside your harddisk. You go from firmware -> partition layout -> bootloader (grub) -> kernel.

The firmware is closed source under BIOS or UEFI or if you're hardcore open source, libreboot/coreboot/'other options' and is located somewhere on your motherboard on some chip.
Then there's the partition layout and bootloader that are located inside /dev/sda I believe, so inside the device itself, which can be read if you want to take a peek at it.

Now the bootloader located in the boot sector /dev/sda loaded by the firmware located in some chip in the motherboard, has access to the boot partition, where it loads the bootloader's configuration file usually located at /boot/grub/grub.cfg for GRUB. I remember UEFI having some kind of standard bootloader by itself, so it doesn't even need a bootloader if I can remember correctly.

This what I recall as it was quite complicated for me too. Especially with software being called firmware and not being called motherbootware or pre-bootware or anything that indicates that this piece of software is the very first thing that starts running during boot.

But you look at /boot and what you can find there. There will be at least two files there called initramfs and vmlinuz, which were also part of the boot process, but I forgot what role those two played.

What's confusing, when x86 initializes it preloads specific address in IP motherboard manufacturer has BIOS there that sets up first 512 bytes. and IP jumps to the new address then it sets up rest of /boot and switches your CPU to real mode up until that point it was in 8bit mode now it is in 16 bit. then jumps to that, now it switches to protected mode I.e. 32bit and loads kernel and initramfs (to solve chicken and egg problem) and then your os boots.

Throw in cryptsetup and shim and switching to 64 bit somewhere there.

If GRUB is too confusing, just uninstall it? You said you have a UEFI system, you don't need a bootloader. You can just put the vmlinuz and initramfs onto the ESP and boot into it directly. You can use efibootmgr to create the boot entry, something like this:

efibootmgr \
	--create \
	--disk /dev/sda \
	--part 1 \
	--index 0 \
	--label "Void linux" \
	--loader /vmlinuz-6.6.52_1 \
	--unicode " \
		root=PARTLABEL=VOID_ROOT \
		rw \
		initrd=\\initramfs-6.6.52_1.img \
		loglevel=4 \
		net.ifnames=0 \
		biosdevname=0 \
		nowatchdog \
		iomem=relaxed \
		"

• --disk /dev/sda: What disk is the esp on?
• --part 1 What partition number (counting from 1) is the esp on?
• --index 0 At what index in the boot menu should the boot entry appear?
• --loader Path to the vmlinuz file. These are normally in /boot, you have to move it to the esp yourself
• root=PARTLABEL=VOID_ROOT this is the linux root partiion. I'm using PARTLABEL to identify mine, but you can use pretty much anything that /etc/fstab supports
• initrd=\\initramfs-6.6.52_1.img Again, you have to move the initramfs file from /boot into the esp. For some reason this uses backslashes, not forward slashes as path separator (double backslashes in this case are to prevent the shell from interpreting it as an escape sequence)
• The rest of the arguments are just misc kernel parameters that I use

Just search for EFISTUB for more info.

Pretty sure the main difference is that one puts stuff in a directory called esp (which I assume is a placeholder for the actual directory?), and the other one is put in /efi. That needs to be the path to your efi partition, because that's where the UEFI expects to find things it can boot. The target is probably redundant, i.e. it defaults to x84_64-efi on Gentoo (maybe not on Arch?) and the id is just a name, you can put whatever there. See man grub-install.

When I'm confused about commands, I find checking the man page for the command a good start to understand what the flags do. Once you've got man-pages installed on your Linux system, you can do "man grub-install" (or any other command) from a terminal to see information about that command and it's flags.

I'm not sure if it says it in the Arch wiki, I think it might, but "esp" is often shorthand for whatever directory you're using as an EFI boot directory, I don't think it's a literal directory. On my Arch system, my esp is "/boot/EFI" I'm pretty sure.

As for why Gentoo doesn't include the --target flag, it could be that "x86_64-efi" is either the default on gentoo's version of grub, or just the default for every version of grub, meaning if the latter is the case, that flag could be safely omitted for your arch installation.

I'm pretty sure the --bootloader-id flag is just a friendly name for the bootloader that you can see from the terminal when booted into a Linux system and probably also from the bios menu. I'm not 100% though, a check through the man page would tell you more about that specific flag. Gentoo may omit it, leaving it either blank, or as some sort of default.

To answer your original question, the system boots up, does some basic checking of hardware to make sure everything can run okay and that there are no obvious faults or incompatibilities, then tries to load a program called a "bootloader" (such as grub), which will then hand off execution to whichever operating system you select. If you're not fond of grub, good news! There are plenty of other good bootloaders available. I'm a big fan of rEFInd (UEFI only) or systemd-boot.

I don't know grub SUPER well, but I'm pretty sure it gets installed in that --efi-directory location that you provide when you run the command. It might be nested a few directories down though, not sure.