When su replaced login for becoming another UNIX login (opens in new tab)

I’ve mentioned it before, but Chris Siebenmann is basically the Raymond Chen of the UNIX world, and today he’s filling that role perfectly once again. I recently read Simon Tatham’s Nitpicking the shell history scene in Tron: Legacy, where one thing that surprised Tatham was the film using ‘login -n root‘ to become root instead of ‘su‘. This surprised me because I found that perfectly ordinary, and this turns up both a bit of Unix history and a difference between modern Unixes. Plain ‘su‘ can...