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 .
- Rd.break – enters emegency mode with no system disk loaded
- emergency – similar to rd.break but mounts system disk
- 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
Now type passwd to change root password
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:
Now mount disks as read only
mount -o ro,remount /sysroot