Why use FUSE for real filesystems

During the initialization phase, the computer hardware is set up and the devices are prepared. This process is different for each device, depending on the hardware architecture.

SUSE Linux Enterprise Desktop uses the GRUB 2 boot loader for all architectures. Depending on the architecture and firmware, starting the GRUB 2 boot loader may be a process with several steps. The purpose of the boot loader is to load the kernel and the original RAM-based filesystem (initramfs). For more information on GRUB 2, see Chapter 14, The boot loader GRUB 2.

12.2.1.1 Initialization and bootloader phase on AArch64 and AMD64 / Intel 64 # Edit source

After switching on the computer, the BIOS or the UEFI initializes the screen and the keyboard and tests the main memory. The computer will not access mass storage devices until this stage. Information on the current date, the current time and the most important peripheral devices are then loaded from the CMOS values. When the boot media and their geometry have been recognized, system control is passed from the BIOS / UEFI to the bootloader.

A traditional BIOS-equipped computer can only load code from the first 512-byte physical data sector (master boot record, MBR) on the boot hard drive. Only the minimalist version of GRUB 2 fits into the MBR. Its only job is to load a core image of GRUB 2 that contains the file system drivers from the gap between the MBR and the first partition (MBR partition table) or the BIOS boot partition (GPT partition table). This image contains file system drivers and is therefore able to access them in the root file system. contains additional modules for the core of GRUB 2 as well as the kernel and the initramfs image. As soon as GRUB 2 has access to this partition, it loads the kernel and the initramfs image into memory and transfers control to the kernel.

If a BIOS system is booted from an encrypted file system that has an encrypted partition, you must enter the decryption password twice. First it needs GRUB 2 to decrypt, the second input enables the encrypted volumes to be mounted.

Booting on UEFI computers is much easier than on computers with a traditional BIOS. The firmware can read a FAT-formatted system partition from hard disks with a GPT partition table. This EFI system partition (mounted as in the running system) offers sufficient space for a complete GRUB 2 application, which is loaded and executed immediately by the firmware.

If the BIOS / UEFI supports network booting, it is also possible to configure a boot server that provides the boot loader. The system can then be booted via PXE. The BIOS / UEFI serves as the boot loader. It receives the boot image from the boot server and starts the system. This process is completely independent of the local hard drives.

12.2.1.2 Initialization and bootloader phase on IBM Z #Edit source

With IBM Z, the boot process must be initialized by a boot loader named (original z program load). Although it supports reading different file systems, it does not support the standard SLE file system (Btrfs) or booting from snapshots. SUSE Linux Enterprise Desktop thus uses a two-stage boot process, which ensures that Btrfs is fully supported at boot time:

  1. boots from the ext2-formatted partition. This partition contains a minimalistic kernel and an initramfs that are loaded into memory. The initramfs contains (among other things) a Btrfs driver and the GRUB 2 boot loader. The kernel is started with the parameter that tells it to start GRUB 2.

  2. The kernel mounts the root file system so that it can be accessed. GRUB 2 is now started via initramfs. The application reads out its configuration and loads the last kernel and the initramfs. The new kernel is now loaded via Kexec.