Runlevel 1, the single-user runlevel, is a bare-bones operating environment intended for system maintenance. In single-user mode, remote logins are disabled, networking is disabled, and most daemons are not started. Single-user mode is used for system configuration tasks that must be performed with no user activity. One common reason you might be forced to use single-user mode is to correct problems with a corrupt filesystem that the system cannot handle automatically.
If you wish to boot directly into single-user mode, you may
specify it at boot time with the kernel’s command line through your
boot loader. For instance, the GRUB boot loader allows you to pass arbitrary parameters
to a kernel at boot time. In order to change the default runlevel,
edit the line that boots your kernel in the GRUB interactive menu,
1 or the word
single to the end of the line to indicate
single-user mode. These arguments are not interpreted as kernel
arguments but are instead passed along to the init process. For
example, if your default GRUB kernel boot line looks like this:
kernel /vmlinuz-18.104.22.168-170.2.56.fc10.i686 ro root=/dev/hda1 rhgb quiet
you can force the system to boot to runlevel 1 by changing this to:
kernel /vmlinuz-22.214.171.124-170.2.56.fc10.i686 ro root=/dev/hda5 rhgb quiet 1
kernel /vmlinuz-126.96.36.199-170.2.56.fc10.i686 ro root=/dev/hda5 rhgb \ quiet single
To switch into single-user mode from another runlevel, you can simply issue a runlevel change command with ...