101.2 BootSystem 2

GRUB (Grand Unified Bootloader).
1. Called by BIOS or UEFI
2. Display a list of SO for boot
3. GRUB menu choose kernels pass new parameters option=Value.
  1. acpi=off
    1. Enables/disables ACPI support.
      1. ACPI "Advanced Configuration and Power Interface
        , convierte la pulsación del botón de apagado en un simple evento
        asignar IRQ a los dispositivos.
  2. init=/bin/bash
  3. systemd.unit=graphical.target
    1. Accept Runlevel 1,S
  4. Mem=512M
    1. used VM
  5. maxcpus=2
    1. Used VM
  6. quiet
    1. Hide boot mssages
  7. vga=ask
    1. will show a list of the available modes of video
  8. root=/dev/sda3
    1. Sets the root partition, distinct from the one pre-configured in the bootloader.
  9. rootflags
    1. options root FS
  10. ro
    1. root FS only Read
  11. rw
    1. writing in root FS during initial mount
  12. Changing the kernel parameters is not usually required
    1. can be useful to detect and solve operating system related problems
/etc/default/grub
1. add Parameters Kernel in line GRUB_CMDLINE_LINUX
2. A new configuration file for the bootloader must be generated every time /etc/default/grub changes,
  1. grub-mkconfig -o /boot/grub/grub.cfg
  2. read in /proc/cmdline
System Initialization
1. Kernel
2. scripts
  1. services o daemons
3. Configuration File
4. SO starts when the bootloader loads the kernel into RAM.
  1. Basic hardware configuration and memory addressing
  2. initramfs (initial RAM filesystem).
    1. 1.- Containing a filesystem used as a temporary root filesystem during the boot process.
    2. 2.- The main purpose of a initramfs file is to provide the required modules so the kernel can access the “real” root filesystem of the operating system.
    3. 3.- As soon as the root filesystem is available, the kernel will mount all filesystems configured in /etc/fstab and then will execute the first program, a utility named init
      1. The init program is responsible for running all initialization scripts and system daemons.
      2. SysV standard
        the concept of runlevels. Runlevels are numbered 0 to 6
      3. systemd
        employs sockets and D-Bus for service activation, on-demand daemon execution, process monitoring with cgroups, snapshot support, system session recovery, mount point control and a dependency-based service control
      4. Upstart
        Like systemd, Upstart is a substitute to init.
        The focus of Upstart is to speed up the boot process by parallelizing the loading process of system services
Initialization Inspection
1. Errors may occur during the boot process,
2. kernel ring buffer.
  1. The memory space where the kernel stores its messages
  2. dmesg dmesg --clear
    1. Ver y Limpiar Messages
  3. Systemd
    1. journalctl journalctl -b journalctl --list-boots journalctl -b 0
  4. /var/log
    1. store other messages
    2. journalctl -d /var/log/journal

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101.2 BootSystem 2

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	Created by Rolando Martinez over 3 years ago