Many occasions during commissioning of servers we need to reboot especially to freshen hardware re-configurations. (ain’t that still a bitch). Single user mode is there to help.
Booting into single user mode
At the GRUB splash screen at boot time, press any key to enter the GRUB interactive menu.
Select CentOS 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
singleas a separate word (press the Spacebar and then type
single). Press Enter to exit edit mode.You are in Single User mode.