One of the advantages of single-user mode is that you do not need a boot CD-ROM; however, it does not give you the option to mount the file systems as read-only or not mount them at all.
If your system boots, but does not allow you to log in when it has completed booting, try single-user mode.
In single-user mode, your computer boots to runlevel 1. Your local file systems are mounted, but your network is not activated. You have a usable system maintenance shell. Unlike rescue mode, single-user mode automatically tries to mount your file system. Do not use single-user mode if your file system cannot be mounted successfully. You cannot use single-user mode if the runlevel 1 configuration on your system is corrupted.
On an x86 system using GRUB, use the following steps to boot into single-user mode:
At the GRUB splash screen at boot time, press any key to enter the GRUB interactive menu.
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.