On many computer operating systems, the superuser, or root, is a special user account used for system administration.

Many older operating systems on computers intended for personal and home use, including MS-DOS and Windows 9x, do not have the concept of multiple accounts and thus have no separate administrative account; anyone using the system has full privileges. Separation of administrative privileges from normal user privileges makes an operating system more resistant to viruses and other malware, and the lack of this separation in these operating systems has been cited as one major source of their insecurity.

Unix and Unix-like

In Unix-style computer operating systems, root is the conventional name of the user who has all rights or permissions in all modes (single- or multi-user). Alternative names include baron in BeOS and avatar on some Unix variants. BSD often provides a toor ("root" backwards) account in addition to a root account. The root user can do many things an ordinary user cannot, such as changing the ownership of files and binding to ports numbered below 1024.

It is never good practice for anyone to use root as their normal user account, since simple typographical errors in entering commands can cause major damage to the system. It is advisable to create a normal user account instead and then use the su command to switch when necessary. Some use the sudo utility instead, which allows a measure of graduated access.

Many operating systems, such as Mac OS X and Linux distributions, allow administrator accounts which provide greater access while shielding the user from most of the pitfalls of full root access. In some cases, the root account is disabled by default, and must be specifically enabled. In a few systems, such as Plan 9, there is no superuser at all.

Software defects which allow a user to "gain root" (to execute with superuser privileges code supplied by that user) are a major computer security issue, and the fixing of such software is a major part of maintaining a secure system. One common way of gaining root is to cause a buffer overflow in a program already running with superuser privileges. This is often avoided in modern operating systems by running critical services, such as httpd, under a unique limited account. A related term is rootkit, using root privileges to conceal certain data from the system administrator.

Windows NT

In Windows NT and later systems derived from it (Windows 2000, Windows XP, Windows Server 2003 and Windows Vista), there may or may not be a superuser. By default, there is a superuser named Administrator, although it is not an exact analogue of the Unix root superuser account. Administrator does not have all the privileges of root because some superuser privileges are assigned to the Local System account in Windows NT. However, the Local System account, which is never used by the user, can be used via an exploit that makes Windows run a command prompt as Local System, allowing you to type into it and run anything as Local System.

In Windows Vista or later, you can use User Account Control to run a process with elevated privileges (for example, by right-clicking on the program and selecting Run as administrator). In earlier version of Windows, the command runas fulfils this task (see Microsoft's documentation for runas for more details).

See also

• nobody (username)
• Power user

External links

• root Definition - by The Linux Information Project (LINFO)
• Superuser Privileges - Linux: UBLinux 4 (GNU)
• An Introduction to Mac OS X Security
• Discussion on origin of Charlie Root at pipermail