{{Short description|Computer operating mode, often used for repair or troubleshooting}} {{Multiple issues| {{Technical|date=August 2025}} {{Update|date=August 2025}} {{Refimprove|date=August 2025}} }} '''Single-user mode''' is a mode in which a multiuser computer operating system boots into a single administrator user, instead of the normal system. It is mainly used for maintenance of multi-user environments, including network servers, where operating on the normal system would be difficult or impossible{{snd}} for example, some tasks may require exclusive access to resources that are shared, like repairing a broken filesystem used for a network share. This mode can also be used for security purposes, as network services are not run, eliminating the possibility of outside interference. On some systems, a forgotten superuser password can be changed in single-user mode, although not asking for the password in this case is viewed as a security vulnerability.
==Unix family== 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.
In systems using System V-style runlevels, the runlevel is usually changed using the <code>init</code> command. Selecting a runlevel of 1, or S, will boot into single-user mode.
Boot-loader options can be changed during startup before the execution of the kernel. In FreeBSD and DragonFly BSD, it can be changed before rebooting the system with the command <code>nextboot -o "-s" -k kernel</code>, and its bootloader offers the option on boot to start in single-user mode. In Solaris, the command <code>reboot -- -s</code> will cause a reboot into single-user mode.
In OS X El Capitan and later releases of macOS, a userspace reboot to single-user mode can be performed with the command <code>sudo launchctl reboot userspace -s</code> in Terminal, and the system can be fully rebooted in single-user mode with the command <code>sudo launchctl reboot system -s</code>. On macOS High Sierra and earlier versions, a user can also enter single user mode by holding down {{key press|⌘ S}} at startup,<ref>{{Cite web |title=Mac startup key combinations |url=https://support.apple.com/en-us/102603 |access-date=2025-05-11 |website=Apple Support |language=en}}</ref> which may require entering a password set in the firmware. Single-user mode is different from safe mode in that the system goes directly to the console instead of starting up the core elements of macOS (items in <code>/System/Library/</code>, ignoring <code>/Library/</code>, <code>~/Library/</code>, et al.). From there users are encouraged by a prompt to run fsck or other command line utilities as needed (or installed).
==Microsoft Windows== Microsoft Windows provides Recovery Console, Last Known Good Configuration, Safe Mode and recently the Windows Recovery Environment as standard recovery means. Bootable BartPE-based third-party recovery discs are available.
The Recovery Console and recovery discs are different from single-user modes in other operating systems because they are independent of the main operating system, whereas single-user mode is the same system operating in a different mode.
==References== {{Reflist}} * {{Cite web |url=http://www.linfo.org/runlevel_def.html |title=What is a runlevel? |accessdate=November 17, 2010}} * [https://books.google.com/books?id=KJBYAAAAYAAJ UNIX Research System Programmer's Manual]
{{DEFAULTSORT:Single User Mode}} Category:Operating system technology Category:Booting
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