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The Superuser Story – The History of #root

AuthorMassimiliano Brolli
TranslatorTara Lie

In the beginning there was the Word…

Computers, before passing into the era of transistors, were cyclopean machines – heavy and hungry for electricity. They used thermionic valves or vacuum tubes to work, and then were only able to perform very small computations.

Let’s discuss for example the ENIAC, 1945, the first digital general-purpose computer, created to solve problems regarding the calculation of the ballistic curves of bullets.


The Electronic Numerical Integrator and Computer (ENIAC)

This gigantic computer took up 1800 square feet of space, and would consume about 150 kilowatts of power. It is said that the very first time it was switched on, all of the lights in the district of Philadelphia went out due to the enormous electrical load. 

It wasn’t the only one however; there was the EDVAC, the UNIVAC and a whole series of large transistor computers such as the IBM and the DEC PDPs. The PDP line began with the PDP-1, AND as discussed in the previous article, was used by Steve Russell to create the first video game equipped with a Gamepad, which was entitled “Spacewar!”.

In short, many of these large computers were produced – by IBM, DEC and General Electric – but we will explore the latter, or more precisely the GE-600, a family of mainframe computers originating in the 1960’s. 


Important developments were started on the GE-600 in 1964. It was the production of an operating system called Multics – an acronym of ‘Multiplexed Information and Computing Service’, which we can undoubtedly cite as the genesis of modern operating systems.

Multics was created by a joint effort between MIT’s Project MAC, together with General Electric and Bell Laboratories. Project MAC was led by the great Fernando Corbatò, whom we have been introduced to in a RedHotCyber video as the inventor of the password and user profile.


The Multics system was a mainframe time-sharing operating system which was truly innovative for its time. It was written in PL/I, a 3rd generation programming language developed at the beginning of the 60s as an alternative to the Assembler.


It was the first operating system to introduce a hierarchical file system, like in the computers of today, and to have a command processor such as the common shells. Additionally, the concept of an Access Control List was introduced, along with online reconfiguration – the ability to add or remove memory banks and disk drives while the computer is running.

Multics, as we have mentioned, introduced the concept of a hierarchical file system, and the principle directory in the operating system came to be called “root”. Root referred to the root of the tree of directories that were stored on the physical volume that contained the partition where the root directory was located.

In 1969, Ken Thompson began to write the first version of THE operating system UNIX in code assembler on a PDP-7 at Bell Laboratories. He too called the privileged user, or superuser, “root”, probably inspired by the multics operating system, which he had worked with previously.

According to LinuxInfo, the use of the term “root”, the all-powerful admin user, could be derived from the fact that root is the only account with write permissions (that is, has permission to modify files) in the entire file system tree.


The root directory, in turn, is named to reflect the tree structure design of filesystems (the entire directory hierarchy used to organise files) in Unix-like operating systems; all the directories branch off from a single one that is analogous to the root of a tree.

Multics was released in 1969, around the time that Ken Thompson started writing UNIX.

There are no reliable sources on the root user history, but presumably Ken Thompson, inspired by Multics, gave the name “root” to the superuser, as the absolute master of the directory and file tree in an operating system.



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