On an x86 system using GRUB as the boot loader, use the following steps to boot into single-user mode:
If you have a GRUB password configured, type p and enter the password.
Select Red Hat Enterprise Linux with the version of the kernel that you wish to boot and type a to append the line.
Go to the end of the line and type single as a separate word (press the [Spacebar] and then type single). Press [Enter] to exit edit mode.
Back at the GRUB screen, type b to boot into single-user mode.
On an x86 system using LILO as the boot loader, at the LILO boot prompt (if you are using the graphical LILO, you must press [Ctrl]-[x] to exit the graphical screen and go to the boot: prompt) type: