Single-user mode is a mode in which a

multiuser Multi-user software is computer software that allows access by multiple users of a computer. Time-sharing systems are multi-user systems. Most batch processing systems for mainframe computers may also be considered "multi-user", to avoid leavin ...

computer

operating system An operating system (OS) is system software that manages computer hardware and software resources, and provides common daemon (computing), services for computer programs. Time-sharing operating systems scheduler (computing), schedule tasks for ...

boots A boot is a type of footwear. Most boots mainly cover the foot and the ankle, while some also cover some part of the lower calf. Some boots extend up the leg, sometimes as far as the knee or even the hip. Most boots have a heel that is clearl ...

into a single

superuser In computing, the superuser is a special user account used for system administration. Depending on the operating system (OS), the actual name of this account might be root, administrator, admin or supervisor. In some cases, the actual name of the ...

. 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 


The system utility fsck (''file system check'') is a tool for checking the consistency of a  file system in Unix and Unix-like operating systems, such as Linux 






Linux ( ) is a family of open source Unix-like operating systems based on the L ...

on a

network share In computing, a shared resource, or network share, is a computer resource made available from one host to other hosts on a computer network. It is a device or piece of information on a computer that can be remotely accessed from another comput ...

. This mode can also be used for security purposes network services are not run, eliminating the possibility of outside interference. On some systems a lost

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.

Unix family

Unix-like A Unix-like (sometimes referred to as UN*X, *nix or *NIX) operating system is one that behaves in a manner similar to a Unix system, although not necessarily conforming to or being certified to any version of the Single UNIX Specification. A Uni ...

operating systems provide single-user mode functionality either through the System V-style

runlevel A runlevel is a mode of operation in the computer operating systems that implements Unix System V-style initialization. Conventionally, seven runlevels exist, numbered from zero to six. ''S'' is sometimes used as a synonym for one of the levels. ...

s, 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. Boot-loader options can be changed during startup before the execution of the kernel. In

FreeBSD FreeBSD is a free-software Unix-like operating system descended from the Berkeley Software Distribution (BSD). The first version was released in 1993 developed from 386BSD, one of the first fully functional and free Unix clones on affordable ...

and

DragonFly BSD DragonFly BSD is a free and open-source Unix-like operating system forked from FreeBSD 4.8. Matthew Dillon, an Amiga developer in the late 1980s and early 1990s and FreeBSD developer between 1994 and 2003, began working on DragonFly BSD in ...

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. In

Solaris Solaris is the Latin word for sun. It may refer to: Arts and entertainment Literature, television and film * ''Solaris'' (novel), a 1961 science fiction novel by Stanisław Lem ** ''Solaris'' (1968 film), directed by Boris Nirenburg ** ''Sol ...

the command reboot -- -s will cause a reboot into single-user mode. In

OS X El Capitan OS X El Capitan ( ) () is the twelfth major release of macOS (named OS X at the time of El Capitan's release), Apple Inc.'s desktop and server operating system for Macintosh. It focuses mainly on performance, stability, and security. Followi ...

and later releases of

macOS macOS, previously OS X and originally Mac OS X, is a Unix, Unix-based operating system developed and marketed by Apple Inc., Apple since 2001. It is the current operating system for Apple's Mac (computer), Mac computers. With ...

, 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 macOS High Sierra (version 10.13) is the fourteenth major release of macOS, Apple Inc.'s desktop operating system for Macintosh computers. macOS High Sierra was announced at the WWDC 2017 on June 5, 2017 and was released on September 25, 201 ...

and earlier versions, a user can also enter single user mode by holding down after powering the system, which may require the use to enter a password set in the

firmware In computing Computing is any goal-oriented activity requiring, benefiting from, or creating computer, computing machinery. It includes the study and experimentation of algorithmic processes, and the development of both computer hardware, h ...

. Single-user mode is different from a

safe mode Safe mode is a diagnosis, diagnostic mode of a computer operating system (OS). It can also refer to a mode of operation by application software. ''Safe mode'' is intended to help fix most, if not all, problems within an operating system. It is a ...

boot 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 The system utility fsck (''file system check'') is a tool for checking the consistency of a file system in Unix and Unix-like operating systems, such as Linux Linux ( ) is a family of open source Unix-like operating systems based on the L ...

or other

command line A command-line interface (CLI) is a means of interacting with software via command (computing), commands each formatted as a line of text. Command-line interfaces emerged in the mid-1960s, on computer terminals, as an interactive and more user ...

utilities as needed (or installed).

Microsoft Windows

Microsoft Windows Windows is a Product lining, product line of Proprietary software, proprietary graphical user interface, graphical operating systems developed and marketed by Microsoft. It is grouped into families and subfamilies that cater to particular sec ...

provides

Recovery Console The Recovery Console is a feature of the Windows 2000, Windows XP and Windows Server 2003 operating systems. It provides the means for administrators to perform a limited range of tasks using a command-line interface. Its primary function is to ...

, Last Known Good Configuration,

Safe Mode Safe mode is a diagnosis, diagnostic mode of a computer operating system (OS). It can also refer to a mode of operation by application software. ''Safe mode'' is intended to help fix most, if not all, problems within an operating system. It is a ...

and recently

Windows Recovery Environment Windows Preinstallation Environment (also known as Windows PE and WinPE) is a lightweight version of Microsoft Windows, Windows used for the deployment of PCs, workstations, and servers, or troubleshooting an operating system while it is offlin ...

as standard recovery means. Also, bootable

BartPE BartPE (Bart's Preinstalled Environment) is a discontinued tool that customizes Windows XP or Windows Server 2003 into a lightweight environment, similar to Windows Preinstallation Environment, which could be run from a Live CD or Live USB drive ...

-based third-party recovery discs are available. Recovery Console and recovery discs are different from single-user modes in other operating systems because they are independent of the maintained operating system. This works more like

chroot chroot is a shell (computer), shell command (computing), command and a system call on Unix and Unix-like operating systems that changes the apparent root directory for the current running process and its Child process, children. A program that i ...

ing into other environment with other kernel in Linux.

References

*
UNIX Research System Programmer's Manual
Operating system technology Booting {{Comp-sci-stub