I forgot my root password, how can I get into my system?

Issue:
I forgot my root password, how can I get into my system? Resolution:You can change your root password from single user mode or rescue mode. Getting into single use mode depends on your bootloader:

GRUB
Booting into single user mode using GRUB is accomplished by editing the kernel line of the boot configuration. This assumes that either the GRUB boot menu is not password protected or that you have access to the password if it is.

If the GRUB boot menu is password protected and you do not have access to the password, then you will need to use a rescue disk to boot the system. Follow the instructions given by the rescue disk boot process to recover your installation and then chroot to your system image (usually accomplished by issuing the command chroot /mnt/sysimage). From this point you should be able to use the passwd to change the root password of the system.

At the boot prompt, select the kernel that you wish to boot with and press 'e' (for edit). You will now be taken to a screen where you can edit the boot parameters. Move the cursor to the kernel line and press 'e' again. Now append an 'S' to the end of the line, press Return, and then 'b' (for boot). The system will now start in single user mode and you can change the root password using the passwd command.

LILO
When the system comes to the LILO: prompt, type linux single . When you get the # prompt you will need to type passwd root. This will update the password to a newer one. At this point you can type exit and your system should return to the boot sequence. Alternatively, you can reboot your system with the shutdown -r now or reboot commands. The system should boot up normally. You can now use your new root password to gain root access.

If LILO is configured to not wait at the boot menu (timeout value in /etc/lilo.conf set to 0) you can still halt the boot process by pressing any key in the split second before LILO boots the kernel.