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dhruvdutt/linux_boot_process.md

Last active July 28, 2017 07:44
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Linux Boot Process
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linux_boot_process.md

1. BIOS or UEFI

2. MBR or GPT

1st sector of bootable disk. /dev/hda or /dev/sda

3. Bootloader

GRUB or Windows boot loader. Or custom bootloaders like Clover & Chameleon Detects multiple kernel images, has knowledge of file-system /boot/grub/grub.conf. Also, /etc/grub.conf points to same file.

4. Kernel

Mounts root file system from grub.confg's root= value (hd0,0); executes /sbin/init program, initrd, init ram disk - temp file system until root file system is mounted.

5. Init

Looks at /etc/inittab to decide linux run level 0-6 init starts applications from /etc/rc.d/rc0.d, rc0.d, rc1.d

Run levels:

  1. halt
  2. single user moden, no deamons, only root login
  3. multi user mode without network interfaces, no daemons
  4. starts system normally
  5. undefined
  6. x11 => 3 + display manager(x) - used in GUI env
  7. reboot

6. Run-levels

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