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The Meaning of ’su’

When I taught for Guru Labs, part of the students training was covering different ways of becoming the root user, such as using “su”, “sudo” and taking advantage of the wheel group. Login shells versus non-login shells were also covered. The idea was to help the student understand the real nature of the shell and subshells, not to mention how to appropriately switch user accounts.

Inevitably, I would be asked what the meaning of “su” really stood for. This seems to be the Great Question in Unix (aside from the creat() command in C lacking an ‘e’). When I first started with Unix back in 1999, I was always under the impression that “su” meant “super user”, as the only time I ever used the command was to become root. My learning was on Solaris 7, and even my colleagues agreed that “su” meant “super user”.

After discovering Linux, and having it installed as a virtual machine on my own hardware (yes, VMWare existed back then), I started tinkering, and I found that you could use “su” to switch to more users than just root. This shook the very foundation that I had learned Unix on.

So, what does “su” mean?

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