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| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| Single-user mode | 1/1 | https://en.wikipedia.org/wiki/Single-user_mode | reference | science, encyclopedia | 2026-05-05T11:38:56.797507+00:00 | kb-cron |
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 – 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 init 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 nextboot -o "-s" -k kernel, and its bootloader offers the option on boot to start in single-user mode. In Solaris, the command reboot -- -s 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 sudo launchctl reboot userspace -s in Terminal, and the system can be fully rebooted in single-user mode with the command sudo launchctl reboot system -s. On macOS High Sierra and earlier versions, a user can also enter single user mode by holding down ⌘ S at startup, 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 /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).
== 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 ==
"What is a runlevel?". Retrieved November 17, 2010. UNIX Research System Programmer's Manual