OpenWest 2014/Booting Linux

by Mike Lovell

Slides - http://baldr.dev-zero.net

• http://baldr.dev-zero.net/openwest-2014-booting-a-linux-system.pdf

Boot Process: Platform Init -> Bootloader -> Kernel Init -> Init

Platform Init:

• Firmware boot
• BIOS (Award, AMI, Phoenix, Coreboot on Chromebooks)
• UEFI
• Low level hardware initialization
• Pass control from BIOS to bootloader:
  • Find boot loader through MBR or GPT
  • Preboot eXecution Environment (PXE)

Bootloader:

• Grub, Lilo, Syslinux, uBoot, iPXE
• Loads and execute kernel

Kernel Init:

• reinitialize hardware with OS drivers
• load kernel modules
• initrd (old) / initramfs (newer)
• mount root

Init:

• First process the kernel runs
• Kernel Process PID 1
• Responsible for starting all other applications
• Traditionally been sysvinit, now upstart/systemd/openrc

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UEFI

• (Unified) Extensible Firmware Interface
• Most implementations based on the Open Source reference implementation, Tianocore
• GPT
  • Supports GPT and larger than 2TB boot drives
  • EFI System Partition Table
  • Default application at EFI\Boot\bootx64.efi
• Secure Boot
• Not DRM