Single user mode

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Single user mode is a mode in which a multiuser computer operating system boots into a single superuser. It is mainly used for maintenance of multi-user environments such as network servers. Some tasks may require exclusive access to shared resources, for example running fsck on a network share. This mode may also be used for security purposes - network services are not run, eliminating the possibility of outside interference. On some systems a lost superuser password can be changed by switching to single user mode, but not asking for the password in such circumstances is viewed as a security vulnerability.

[edit] Mac OS X

Mac OS X users can accomplish this by holding down ⌘S after powering the system. The user may be required to enter a password set in the firmware. Single User Mode is different from a Safe Mode boot in that the system goes directly to the console instead of starting up the core elements of Mac OS X (items in /System/Library/, ignoring /Library/, ~/Library/, et al.). From there users are encouraged by a prompt to run fsck or other command line utilities as needed (or installed).Visit [1]

[edit] Microsoft Windows

Microsoft Windows provides Recovery Console. It is different from single user modes in other operating systems because it is independent of the maintained operating system.

[edit] Unix family

Unix-like operating systems provide single user mode functionality through runlevels. Runlevels are usually changed using the init command, runlevel 1 or S will boot into single user mode.