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High level process for RHEL up to version 6.x

 

 

1 BIOS Basic Input Output System, reads MBR
2 MBR Master boot code (frst stage boot loader) executed, Locates Grub (2nd stage boot loader)
3 Grub Grand Unified Bootloader, determines which kernel to execute, loads kernel and initrd images
4 Kernel OS kernel executed (vmlinuz-<version>), initrd used by kernel as temporary root file system (on ramdisk) until real root file system is mounted
5 Init Looks at /etc/inittab to decide the Linux run level
  • 0 – halt
  • 1 – Single user mode
  • 2 – Multiuser, without NFS
  • 3 – Full multiuser mode
  • 4 – unused
  • 5 – X11
  • 6 – reboot
6 Runlevels Starts run level programs