GRUB2 – RH/Centos7

Interrupt Boot process to gain access to a system to change password

  1. When Grub appears press E
  2. At the end of the image entry enter “rd.break
  3. Press Ctrl-x
  4. You will now boot into init RAM FS.
  5. Mount the sysroot directory  “mount -oremount,rw /sysroot/
  6. Change root into sysroot “chroot /sysroot/
  7. Change root password “passwd” 
  8. If SELInux is enabled you will need to re-label all files by creating file in the / directory of sysroot called .autorelabel
  9. Exit.

How to boot to a different targets
During boot when Grub2 appears press e and at the end of the image enter one of the following:
systemd.unit=multi-user.target” or “systemd.unit=emergency.target

General Settings of GRUB2

The file you are interested in is /etc/default/grub. You can edit this file but you will have to run the following command in order for the changes to take affect.

grub2-mkconfig -o /boot/grub2/grub.cfg

To get the list of the kernels displayed at boot time, type:

grep ^menuentry /boot/grub2/grub.cfg

To permanently define the kernel to execute at boot time

grub2-set-default 0
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