For Red Hat Enterprise Linux 6
Single-User Mode
Single-user mode provides a Linux environment for a single user that allows you to recover your system from problems that cannot be resolved in networked multi-user environment. You do not need an external boot device to be able to boot into single-user mode, and you can switch into it directly while the system is running.
At the GRUB boot screen, press any key to enter the GRUB interactive menu.
Select Red Hat Enterprise Linux with the version of the kernel that you want to boot and press the a to append the line.
Type single as a separate word at the end of the line and press Enter to exit GRUB edit mode. Alternatively, you can type 1 instead of single.
Emergency Mode
Emergency mode, provides the minimal bootable environment and allows you to repair your system even in situations when rescue mode is unavailable. In emergency mode, the system mounts only the root file system, and it is mounted as read-only. Also, the system does not activate any network interfaces and only a minimum of the essential services are set up. The system does not load any init scripts, therefore you can still mount file systems to recover data that would be lost during a re-installation if init is corrupted or not working.
At the GRUB boot screen, press any key to enter the GRUB interactive menu.
Select Red Hat Enterprise Linux with the version of the kernel that you want to boot and press the a to append the line.
Type emergency as a separate word at the end of the line and press Enter to exit GRUB edit mode.
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