Como inicializo o single modo de usuário do GRUB?
Select (highlight) the GRUB boot menu entry you wish to use.
Press e to edit the GRUB boot commands for the selected boot menu entry.
Look near the bottom of the list of commands for lines similar to
linux /boot/vmlinuz-3.2.0-24-generic root=UUID=bc6f8146-1523-46a6-8b6a-64b819ccf2b7 ro quiet splash initrd /boot/initrd.img-3.2.0-24-generic
Change the middle line in (3) by adding the kernel boot parameter single to the end of the line (i.e. after ro quiet splash). For this example you would change
6a-64b819ccf2b7 ro quiet splash
to
6a-64b819ccf2b7 ro quiet splash single
Press either Ctrl+X or F10 to boot using these kernel options.