Superuser

On path: User

Depends on	User • Security

Known by different names in different systems the superuser (root, admin, administrator) is able to obtain privileges not available to ordinary users. These typically include running processes in privileged mode(s) and the ability to modify features such as file permissions.

One user identifier (UID) is used to identify the “superuser”. A superuser can ‘become’ any other user, reset password entries etc.

Because the superuser can do anything – possibly inadvertently – it is not usually a good idea to assume this privilege except when necessary.

Note that superuser is not the same as a privileged mode in the hardware: it is a software privilege. A superuser’s applications will normally run (most of the time) in an unprivileged (“user”) hardware mode. When servicing exceptions, such as system calls, the hardware privilege will be raised (to allow access to hardware peripherals, protected memory etc. but the process will still be owned by its original user.

In practice there need not be much difference between the superuser and other user privileges. For example, the Unix superuser (“root”) can allow or forbid access to a particular hardware port because (s)he owns the corresponding ‘file’ (in /dev/) and can thus change the ‘file permissions’; other users cannot. There are a few calls which are only allowed by root though – perhaps most notably the abilities to change UID and change the ownership of a file/resource.

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"Everything is a File" • Application Binary Interface (ABI) • Arrays • Boot • Buffer Overflow • Containers • Daemons • Disk Partition • Dynamic Memory Allocation • Emulator traps • Environment Variables • Errors • Exceptions • File Attributes • File Locking • File Permissions • Introduction to Operating Systems • Journalling File System • Links • Locks • Man(ual pages in Unix) • Memory Mapped Files • Monitoring • Network File System (NFS) • PATH • Pipes • Pointers • Relocatable Code • Reset • SETUID • Shell • Sockets • Spooling and Buffering • Streams • Structures • Superuser • System Calls • Unix Signals • User • Using Peripherals