When booting the workstation, the bootloader GRUB allows you time for selecting your operating system. On that screen, follow the following steps:
1 – Highlight/select the distro (Red Hat Linux) using the arrow keys.
2 – Press ‘e’ to edit the boot parameters for the distro.
3 – You will see some entries like the following ones:
kernel /vmlinuz-2.4.20-8 ro root=LABEL=/
3 – Highlight/select the line for the Kernel parameters. In the above example, it is the second line which is in bold. Press ‘e’ when you have selected it.
4 – Add ‘single at the end of the line. Don’t forget to put a space between the last character and ‘single’ or ‘1’. Example:
kernel /vmlinuz-2.4.20-8 ro root=LABEL=/ single
5 – Press ‘Enter’ or ‘Return’ key for saving the changes and then ‘b’ for booting.
6 – Once the system boots and you arrive at the command line interface, use the passwd command to change the root password as below:
7 – Follow the instructions to enter new password twice.
8 – Once done, type ‘reboot’ or ‘exit’ to boot again. The new password you set will now work.
Moral : Always keep a password for GRUB