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On many computer operating systems, "SuperUser" is the term used for the special user account that is controlled by the system administrator.

SuperUser: 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).

The user root can do many things an ordinary user cannot, such as changing the ownership of files and binding to ports numbered below 1024. Generally, it is not good practice for anyone to use root as their normal user account, because simple typographical errors can cause major damage to the system. It is recommended 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, allow administrator accounts which provide greater access while shielding the user from most of the pitfalls of full root access.

Software defects which allow a user to "gain root" (to execute with superuser privileges code supplied by that user) are a major 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.

If a person "has root access", it means that they are able to act as the administrator of that computer. The name Charlie Root is often associated with the root account, named after the baseball player of the same name.

SuperUser: MS DOS and Earlier version of Windows

DOS and the DOS-based versions of Microsoft Windows (i.e. Windows 3.x, Windows 95, Windows 98, and Windows Me), are not multi-user operating systems, and there is no distinguished superuser account. Effectively any user of the system has administrator privileges. Separation of administrative privileges from normal user privileges makes an operating system more resistant to viruses and other malicious software, and the lack of this separation in these operating systems has been cited as one major reason why these operating systems are less secure.

SuperUser: Windows XP and Higher

In Windows NT and later systems derived from it (Windows XP, Windows Server, Windows 7, etc), 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.

To run a program as a superuser in Windows XP and later versions of Windows, use the command runas. See Microsoft's documentation for runas for more details.

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