Boot Process

UEFI vs BIOS

Hardware sources

• PXE (pre-boot execution environment)
  • install operating system online
• iPXE(uses HTTPS)

See the init boot procsse right from grub

cat /proc/cmdline

dmesg | head 

---

Grub 2

Steps

• POST(power on self)

  • Turning On for the system firemwer

• Selecting Bootable device

  • Either From UEFI or for the bios

• Loding the boot loader (Grub or Grub2)

• Loading the Kernel

• Loading initramfs

  • On Rehl it also contains the complate OS

• Starting /sbin/init

  • And loading systemd-udev daemon

• Process initrd.target(ececute all units to create minimal env)

  • mounting root file system on /sysroot

• Switch to rootfs

  • Runing the default target afterwards

Changing the root password

1. Enter the rescue mode
2. Add this line before intird

   init=/bin/bash 
   

3. Then boot
4. Mount the system in rw perrmison to be able to applay changes

   mount -o remount,rw /
   # And then back to readonly 
   mount -o remount,ro /
   

   Rembert to .autorelabel for SELinux
5. reboot the system

exec /sbin/init 6
# or 
exec /usr/lib/systemd/systemd

restet root pass init