Linux Administration/System Architecture/Boot Sequence

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This lesson covers the boot sequence.

Objectives and Skills[edit | edit source]

Objectives and skills for the boot sequence portion of Linux+ certification include:[1]

  • Boot the system
    • Provide common commands to the boot loader and options to the kernel at boot time
    • Demonstrate knowledge of the boot sequence from BIOS to boot completion
    • Understanding of SysVinit and systemd
    • Awareness of Upstart
    • Check boot events in the log file
    • The following is a partial list of the used files, terms and utilities:
      • dmesg
      • BIOS
      • bootloader
      • kernel
      • initramfs
      • init
      • SysVinit
      • system

Readings[edit | edit source]

  1. Wikipedia: Linux startup process
  2. Wikipedia: BIOS
  3. Wikipedia: Booting
  4. Wikipedia: GNU GRUB
  5. Wikipedia: Kernel (operating system)
  6. Wikipedia: Upstart (software)
  7. Wikipedia: dmesg
  8. Wikipedia: Initial ramdisk
  9. Wikipedia: init

Multimedia[edit | edit source]

  1. YouTube: Common Boot Loader Commands
  2. YouTube: Understanding the Linux Boot Process
  3. YouTube: An Overview of the Linux Boot Log Files

Activities[edit | edit source]

  1. Complete the tutorial IBM: Learn Linux, 101: Boot the system
  2. Use the GRUB boot menu.
    • Access the GRUB menu. Review available options and advanced options.
    • Edit one of the GRUB menu items to see the configuration but do not make any changes.
    • Access the command line. Use the reboot command to reboot the system.
    • Review Ubuntu: RecoveryMode. Boot into Recovery mode and review available options. Reboot the system.
  3. List the steps in the boot sequence from BIOS to boot completion.
  4. Identify which major Linux distributions use or used init, SysVInit, systemd, and Upstart.
  5. Compare the contents of /var/log/kern.log with the output from dmesg.

Lesson Summary[edit | edit source]

  • The boot sequence includes ROM, Power-On Self-Test (POST), boot manager, boot loader, and user software or graphical user interface (GUI).[2]
  • A master boot record (MBR) is a special type of boot sector at the very beginning of partitioned computer mass storage devices like fixed disks or removable drives intended for use with IBM PC-compatible systems and beyond.[3]
  • Boot loaders interact with the BIOS to load the operating system.[4]
  • System V SysVinit startup is based on runlevels. SysVinit runlevels include:[5]
    • 0 - Shutdown
    • 1 - Single-user mode
    • 2 - Multi-user mode
    • 3 - Multi-user mode with RFS
    • 4 - Multi-user mode, User-definable
    • 5 - Halt
    • 6 - Reboot
    • S - Single-user mode with terminal console
  • Upstart is an event-based replacement for the traditional init daemon.[6]
  • Upstart was the default init system in Ubuntu and Chrome OS.[7]
  • systemd is now the default init system in most Linux distributions, [8] including RHEL and Ubuntu.
  • GRUB boot options include a list of operating systems, "e" to edit the list, and "c" for a command-line.[9]
  • GRUB recovery mode provides a Recovery Menu of options.[10]
  • dmesg (display message or driver message) is a command on most Unix-like operating systems that prints the message buffer of the kernel.[11]

Key Terms[edit | edit source]

ELILO (EFI Linux Loader
EFI/UEFI boot loader[12]
GRUB (GRand Unified Bootloader)
A boot loader package from the GNU Project.[13]
initramfs (initial RAM file system)
A scheme for loading a temporary root file system into memory.[14]
initrd (initial ramdisk)
A scheme for loading a temporary root file system into memory.[15]

References[edit | edit source]