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.However, requiring a user to validate his superuser status for simple administrative functions can inconvenience the administrator as he is required to repeatedly enter his login information.
Unix and Unix-like
In
Unix-style computer
operating systems,
root is the conventional name of the user who has all rights or permissions (to all files and programs) 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 for better usability while performing administrative tasks. Regardless of the name, the superuser always has zero user ID. The root user can do many things an ordinary user cannot, such as changing the ownership of files and binding to network
ports numbered below 1024. The etymology of the term may be that root is the only user account with permission to modify the
root directory of a Unix system.
The first process
bootstrapped in a Unix-like system, usually called
init, runs with root privileges. It spawns all other processes directly or indirectly, which inherit their parents' privileges. Only a process running as root is allowed to change its user ID to that of another user; once it's done so, there is no way back. Doing so is sometimes called
dropping root privileges and is often done as a security measure to limit the damage from possible contamination of the process. Another case is
login and other programs that ask users for credentials and in case of successful
authentication allow them to run programs with privileges of their accounts.
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. The
sudo utility can also be used instead to allow a measure of graduated access.
Many operating systems, such as
Mac OS X and some
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.
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. The user may gain access to the Local System account by making Task Scheduler start a command prompt. Since Task Scheduler starts programs as Local System, the user can run any program as Local System. However, this may be regarded as a
vulnerability.
In
Windows Vista or later, you can use
User Account Control to run a process with elevated privileges (for example, by right-clicking (Windows 2000 users must hold the SHIFT key while right-clicking) on the program and selecting
Run as administrator). In earlier version of Windows, the command
runas fulfils this task (see for more details).
Novell NetWare
In
Novell NetWare, the superuser was called "supervisor", later "admin".
See also
