![]() ![]() Telinit 3 # kill -15 GDM and all logged in *GUI* sessions Systemd maps the numbered runlevels to groups of unit files to launch: `systemctl restart gdm` restarts the GDM Gnome Display Manager "greeter" login screen, which runs basically runs ~startx after `bash -login`. GDM launches the user's Gnome session upon successful login. On a gnome system, GDM is the GUI process that is launched. Runlevel 5 is runlevel 3 (multi-user with networking) + GUI. The EFI system partition is conventionally /boot/efi on a Linux system and there's a signed "shim loader" that GRUB launches, which JMP- launches the kernel+initrd after loading the initrd into RAM (a "RAM drive") and mounting it as the initial root filesystem /, which is pivot_root'd away from after the copy of /sbin/init (systemd) mounts the actual root fs and launches all the services according to the Systemd unit files in order according to a topological sort given their dependency edges: other ARM devices and most MIPS, RISC-V commonly use U-Boot with Device Tree (as without UEFI or ACPI, there has to be a way to inform the kernel of basic non-PNP hardware and how to communicate with it).īooting process of Windows NT since Vista: The only difference is if you are using a distribution that has a signed bootloader (using Microsoft's UEFI CA) probably also check whether the kernel and 3rd party modules are signed using distribution's or your (owner's) signing keys. The firmware then loads the configured UEFI application and runs it (it also provides services for input devices, disks, networking, display). UEFI doesn't look for boot drives but for EFI applications (bootloaders) on a special EFI System Partition (uses FAT32 filesystem per spec, but can be any filesystem your UEFI firmware has a driver for). UEFI works similarly, but is cross-platform (can work on x86, x86_64, itanium, 32bit and 64bit ARM, possibly on RISC-V). Once you select or manually type the path to a kernel and init ram disk, GRUB loads it into memory and jumps to it (still in 16bit real mode). Grub stage 2 then loads it's own drivers for filesystems, searches partitions and kernels+ramdisks. Stage 2 is commonly saved in the empty space before the first partition. GRUB2 is saved to the disk in two stages: Stage 1 is <512bytes and is only used to load stage 2. Everything else is up to the bootloader (BIOS still provides methods for reading disk, interacting with the keyboard/moues and text or (S)VGA video output). ![]() BIOS loads the first sector (MBR) from the selected boot drive to a fixed memory location and jumps to it. With BIOS, your PC initializes hardware and contains firmware drivers for reading disk drives. Here are a couple of resources I think can help you: ![]()
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