102.2 Install a boot manager

102.2 Install a boot manager

1. BootLoader firts piece to load

   • to load an operating system kernel and hand over control to it.
     • The kernel
       • Load The Necesary Drivers
       • initialize the hardware
       • load the rest of the operating system.

2. Grub Legacy Vs Grub2

   • GRUB Legacy was developed in 1995
   • Grub2
     • a more modular design and better localization / internationalization.
     • many more commands and conditional statements, similar to a scripting language
     • support for themes and graphical boot menus with splash screens,
     • the ability to boot LiveCD ISOs directly from the hard drive

3. BootLoader

   • MBR partitioning scheme,
     • the first 512-byte sector of the disk is called the Master Boot Record
     • secondary boot loader on disk, 32 KB space between the MBR and the first partition, load the SO
     • MBR has limitations on the number of partitions
       • 4 partitions 3 fisica y una extendida
       • maximum disk sizes of 2 TB.
   • GPT
     • To overcome these limitation of MBR
     • part of the UEFI (Unified Extensible Firmware Interface)
     • On systems with UEFI firmware, GRUB is loaded by the firmware from the files grubia32.efi
     • On systems with UEFI firmware, GRUB is loaded by the firmware from the files of 32 or 64
       • grubia32.efi grubia64.efi
         • ESP (EFI System Partition).

4. Contents of the Boot Partition

   • Config file-version
     • stores configuration parameters for the Linux kernel
   • System map-version
     • This is useful when debugging a kind of system failure known as a kernel panic,
   • vmlinux-VERSION
     • Linux kernel z indicate comrimido
   • initrd.img-VERSION
     • contains a minimal root file system loaded into a RAM disk, containing utilities and kernel modules needed so the kernel can mount the real root filesystem.
   • /boot/grub/grub.cfg for GRUB 2 /boot/grub/menu.lst in case of GRUB Legacy
     • modules (in /boot/grub/i386-pc), translation files (in /boot/grub/locale) and fonts (in /boot/grub/fonts).

5. Installing GRUB 2

   • GRUB 2 can be installed using the grub-install
     • non-booting system
       • using a Live CD or rescue disc
     • system boot
     • fdisk utility.
       • whether there is a boot partition
       • fdisk -l /dev/sda
         • list all the partitions
         • Device Boot /dev/sda1 *
           • *:boot partition
     • # mkdir /mnt/tmp # mount /dev/sda1
       • # grub-install --boot-directory=/mnt/tmp /dev/sda1
         • # grub-install --boot-directory=/boot /dev/sda1
           • If you are installing to a system which does not have a boot partition
         • If your system does have a dedicated boot partition,

6. Configuring Grub2

   • /boot/grub/grub.cfg
     • Default configuration (No Editable)
     • To make changes to the GRUB configuration,
       • Edit /etc/default/grub run update-grub
         • grub-mkconfig -o /boot/grub/grub.cfg
         • options of /etc/default/grub
           • GRUB_DEFAULT=
             • This can be a numeric value (like 0, 1)
           • GRUB_SAVEDEFAULT=
             • GRUB_SAVEDEFAULT=true GRUB_DEFAULT=saved to saved, default boot option will always be the last one selected in the boot menu.
           • GRUB_TIMEOUT=
             • 0:No Menu -1:Wait for user 5: wait 5 seconds
           • GRUB_CMDLINE_LINUX=
             • added to entries for the Linux kernel.
           • GRUB_CMDLINE_LINUX_DEFAULT=
             • two menu entries are generated for each Linux kernel, one with the default options and one entry for recovery
           • GRUB_ENABLE_CRYPTODISK=