NotesByLex

Red Hat System Administration III - Unit 19 - Troubleshooting the Boot Process

Lex Toumbourou ·

Linux

The Boot Process and Rescue Mode

  • BIOS
    • What can go wrong
      • Incorrect BIOS settings
    • Troubleshooting
      • Vendor specific
  • GRUB
    • Loads initial ram file system ("initramfs")
    • Loads and executes kernel
    • Provides kernel's command-line
    • What can go wrong
      • Misconfiguration of bootloader
      • Bad kernel image or init RAM fs
      • Bad kernel command-line
    • Troubleshooting
      • Choose alternative preconfigured menu item
      • Choose 'e' or 'a' and edit kernel
      • Boot into single-user mode
      • Boot with init=/bin/bash
  • Kernel
    • Detects hardware devices
    • Loads device drivers
    • Mount the root file system image
    • Start the initial process, init
    • What can go wrong?
      • Bad initial RAM file system image
      • Badly identified root file system
      • Corrupted root file system

  • init and Upstart

    • The first userspace process started on the machine is /sbin/init. The init process is responsible for completing the boot process by starting all other non-kernel processes.
    • Fixing a read only mount:
      > mount -o remount,rw /

  • MBR (512 bytes)

    • First 446 bytes - initial boot loader
    • Next 64 bytes - parition table (where is the starting sector and ending sector)
  • The Rescue Shell
    • Mount under /mnt/sysimage
    • Select rescue media
    • Select the type of network settings
    • Follow prompts
    • Can use yum to reinstall stuff