You may be able to boot single-user mode directly. If your system boots but does not allow you to log in when it has completed booting, try single-user mode.
If you are using GRUB, 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 Linux with the version of the kernel that you wish to boot and type e for edit. You will be presented with a list of items in the configuration file for the title you just selected.
Select the line that starts with kernel and type e to edit 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.
If you are using LILO, specify one of these options 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):
boot: linux single boot: linux emergency
In single-user mode, your computer boots to runlevel 1. Your local file systems will be mounted, but your network will not be activated. You will have a usable system maintenance shell.
In emergency mode, you are booted into the most minimal environment possible. The root file system will be mounted read-only, and almost nothing will be set up. The main advantage of emergency mode over single-user mode is that your init files are not loaded. If init is corrupted or not working, you can still mount file systems to recover data that could be lost during a reinstallation.