Rhel 7 boot process

Booting process of Rhel 7 is way different from other rhel distro.

So here we are going to explore the booting process by assuming this , we have grub2  as a boot loader.

@@@@  From Power ON to  Rhel 7 Running  @@@@

  1.    POST (power on self test) test  by BIOS. 
  2.    BIOS  scan for possible boot device and orders them to according to user preferences.
  3.  Boot device are scanned in order for a boot firmware (MBR,PXE ROM,or a partition mark as bootable) , if found then execute it.
  4.   The first stage boot loader stores in  MBR  , which loads the stage 1.5(driver) and stage boot loader from disk and execute it.
  5. Now boot loader loads the configuration file from hard disk in case of grub2  is /boot/grub2/grub.cfg .
  6. Configuration is parsed and based on its contents a boot entry is selected automatically .
  7. The kernel and initial RAMdisk is referenced in the boot entry are located from disk and control is handed over to Kernel.
  8.  Kernel  starts and initialize the hardware using the drivers found in INITRAM disk and a simple init system is also started from the ram disk.
  9. Script  in initram disk mount the root filesystem . then switching root to newly mounted system and hand over control to /sbin/init on the target filesystem that is root.
  10. Now  init mount the filesystem and start services according to configuration.
 

Overview:


 

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