RHCSA: How to change the root password on Red Hat

This is part 4 of the series learning Red Hat. This process has been tested on RHEL8, it works on RHEL7 but any earlier version the process is a little different – often needing a boot disk.

Understanding the boot process

Its important to know how a Linux Operating System Starts .

  • Loads BIOS or UEFI
  • BIOS – basic input/output system
  • UEFI – unified extensible firmware interface
  • Next Loads GRUB2 (Grand Unified Bootloader version 2)
  • To change the root password you break the boot process at GRUB

How to break the boot process

There are 3 ways to break the boot process on Linux. The first 2 ways are manually entered break commands added to the boot.cfg file. The final way is using a boot disk and using rescue mode .

  1. Rd.break – enters emegency mode with no system disk loaded
  2. emergency  – similar to rd.break but mounts system disk
  3. Rescue – like single user mode, disk mounted and services started

To change the root password you must use rdbreak because this process does not mount the system disk, mounting a system disk implements the file system permissions, meaning you cannot change the root password – instead you will be asked for the root password.

How to change the root password:

Ensure you start with your Linux Server powered off.

  • Power on your server
  • At the GRUB2 boot screen press e to edit  boot.cfg
  • Add the command rd.break after the boot image .img as per the picture above
  • Choose to continue the startup process.
  • the rd.break command will break the boot process and you will get a shell prompt
  • Mount the system root using the command
 mount -o rw,remount /sysroot/ 
  • Access the shell by typing
chroot sysroot

Now type passwd to change root password

 passwd  

Important: now you have changed the root password, you must relabel the filesystem so that the files and folders are aware of the new password hashes. Simply type:

touch ./autorelabel

Now mount disks as read only

mount -o ro,remount /sysroot

Then reboot

reboot
Example of the reboot process

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