Single user mode
Encyclopedia
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 can 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.
users can accomplish this by holding down Command-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).
provides Recovery Console
, Last Known Good Configuration, Safe Mode
and recently Windows Recovery Environment as standard recovery means.
Also, bootable BartPE
-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.
Unix-like
operating systems provide single user mode functionality either through the SystemV style runlevel
s or to the BSD style boot-loader options.
Run levels are 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.
On FreeBSD and DragonFly BSD it can be changed before rebooting the system with the command nextboot -o "-s" -k kernel. On Sun Solaris it can be changed with the command reboot -- -s.
Operating system
An operating system is a set of programs that manage computer hardware resources and provide common services for application software. The operating system is the most important type of system software in a computer system...
boots into a single superuser
Superuser
On many computer operating systems, the superuser is a special user account used for system administration. Depending on the operating system, the actual name of this account might be: root, administrator or supervisor....
. 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
Fsck
The system utility fsck is a tool for checking the consistency of a file system in Unix and Unix-like operating systems such as Linux.-Use:...
on a network share. 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 superuser
Superuser
On many computer operating systems, the superuser is a special user account used for system administration. Depending on the operating system, the actual name of this account might be: root, administrator or supervisor....
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.
Mac OS X
Mac OS XMac OS X
Mac OS X is a series of Unix-based operating systems and graphical user interfaces developed, marketed, and sold by Apple Inc. Since 2002, has been included with all new Macintosh computer systems...
users can accomplish this by holding down Command-S after powering the system. The user may be required to enter a password set in the firmware
Firmware
In electronic systems and computing, firmware is a term often used to denote the fixed, usually rather small, programs and/or data structures that internally control various electronic devices...
. Single User Mode is different from a Safe Mode
Safe Mode
Safe mode is a diagnostic mode of a computer operating system . It can also refer to a mode of operation by application software. Safe mode is intended to fix most, if not all problems within an operating system...
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
Fsck
The system utility fsck is a tool for checking the consistency of a file system in Unix and Unix-like operating systems such as Linux.-Use:...
or other command line utilities as needed (or installed).
Microsoft Windows
Microsoft WindowsMicrosoft Windows
Microsoft Windows is a series of operating systems produced by Microsoft.Microsoft introduced an operating environment named Windows on November 20, 1985 as an add-on to MS-DOS in response to the growing interest in graphical user interfaces . Microsoft Windows came to dominate the world's personal...
provides Recovery Console
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 enable administrators to recover from situations...
, Last Known Good Configuration, Safe Mode
Safe Mode
Safe mode is a diagnostic mode of a computer operating system . It can also refer to a mode of operation by application software. Safe mode is intended to fix most, if not all problems within an operating system...
and recently Windows Recovery Environment as standard recovery means.
Also, bootable BartPE
BartPE
BartPE is a lightweight variant of the 32-bit version of Microsoft Windows XP or Windows Server 2003, similar to Windows Preinstallation Environment, which can 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.
Unix family
Unix-like
Unix-like
A Unix-like operating system is one that behaves in a manner similar to a Unix system, while not necessarily conforming to or being certified to any version of the Single UNIX Specification....
operating systems provide single user mode functionality either through the SystemV style runlevel
Runlevel
The term runlevel refers to a mode of operation in one of the computer operating systems that implement Unix System V-style initialization. Conventionally, seven runlevels exist, numbered from zero to six; though up to ten, from zero to nine, may be used. S is sometimes used as a synonym for one...
s or to the BSD style boot-loader options.
Run levels are 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.
On FreeBSD and DragonFly BSD it can be changed before rebooting the system with the command nextboot -o "-s" -k kernel. On Sun Solaris it can be changed with the command reboot -- -s.