Booting Single-User Mode
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
boot: linux single
In single-user mode, you computer boots to runlevel 1. Your local filesystems 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 filesystem will be mounted read-only and almost nothing will be set up. The main advantage of emergency mode over linux single is that your init files are not loaded. If init is corrupted or not working, you can still mount filesystems to recover data that could be lost during a re-installation.
Have you ever rebuilt a kernel and, eager to try out your new handiwork, rebooted before running /sbin/lilo? If you did not have an entry for an older kernel in lilo.conf, you had a problem. If you would like to know a solution to this problem, read this section.
In many cases, you can boot your Red Hat Linux system from the Red Hat Linux boot disk  with your root filesystem mounted and ready to go. Here is how to do it:
Enter the following command at the boot disk's boot: prompt:
linux single root=/dev/hdXX initrd=
Replace the XX in /dev/hdXX with the appropriate letter and number for your root partition.
What does this command do? First, it starts the boot process in single-user mode, with the root partition set to your root partition. The empty initrd specification bypasses the installation-related image on the boot disk, which will cause you to enter single-user mode immediately.
Is there a negative side to using this technique? Unfortunately, yes. Because the kernel on the Red Hat Linux boot disk only has support for IDE built-in, if your system is SCSI-based, you will not be able to do this. In that case, you will have to access rescue mode using the linux rescue command mentioned above.