How to Reset the Root Password in CentOS/RHEL7

Set the new password for the root user by entering a password command in the command line. A weak password may also result in warnings such as “password fails directory check.” You can choose your desired password and disregard the warning.

To reset the root password on CentOS7/RHEL 7, you need:

1. A working GRUB root loader
2. A working operating system

Steps to Reset Root Password on CentOS 7/RHEL 7

Method 1 : Rebooting and Editing Grub2

To force the machine to boot from the default kernel, restart it and hit any key. After choosing the kernel line, press “e” to launch the Grub Edit Mode.

After you press the “e” key, scroll down, go to the Linux 16 line, and remove the rhgb, quiet and LANG parameters.
For moving at the end of the line, press ctrl+e, move to the front, and press ctrl+a.
The Linux16 line will be linuxefi on the UEFI system.

Method 2: Appending the rd.break to kernel

In edit mode, navigate to the line that begins with linux16 and append rd.break to the end of it.

This will make the machine boot into emergency mode, giving you root user privileges without entering a root user password. Even though the root user hasn’t been set, this still works.

Reboot the System

Press CLTR+x after appending the rd.break to the kernel. This will help to reboot the system into emergency mode.

Remounting the sysroot

Firstly, we will remount the sysroot file system in read-write mode and then use the chroot to get into a chroot jail.
# mount -o remount, rw/sysroot
# chroot /sysroot

Resetting the Root Password

To change the root user’s password, type a password command in the command line. If your password is weak, you may even encounter alerts such as “password fails directory check.” You are free to change the password and disregard the warning.

# passwd

SElinux relabeling

All the unlabeled files, which include the shadow files, get relabelled during the booting. The hidden files auto-relabel the files changed outside their regular context, like the file/etc/shadow.

# touch /.autorelabel

Sync

If you want to flush the cache of the disk, type the command given below:
# sync

Reboot

Type the exit command twice and leave the chroot environment and log out. The system will apply some SELinux contexts and reboots.

Conclusion
By following the steps given above, you can easily login to CentOS/RHEL using the new password.