This mode can also be used for security purposes – network services are not run, eliminating the possibility of outside interference.
Unix-like operating systems provide single-user mode functionality either through the System V-style runlevels, BSD-style boot-loader options, or other boot-time options.
The run-level is usually changed using the init command, runlevel 1 or S will boot into single-user mode.
In FreeBSD and DragonFly BSD it can be changed before rebooting the system with the command nextboot -o "-s" -k kernel, and its bootloader offers the option on bootup to start in single-user mode.
From there users are encouraged by a prompt to run fsck or other command line utilities as needed (or installed).