troubleshooting Question

What the purpose of /dev/tty?

Avatar of Maarten Bruins
Maarten Bruins asked on
Unix OSLinuxLinux OS DevShell ScriptingLinux Distributions
5 Comments1 Solution247 ViewsLast Modified:
See: https://stackoverflow.com/questions/6170598/can-anyone-explain-to-me-what-the-purpose-of-dev-tty


You can start with the POSIX spec. From there, read about the "controlling terminal" of a process.

But just for example... /dev/tty is how a command like "ssh" can read your password even if its standard input comes from somewhere else:

tar cf - . | ssh dest 'tar xf -'

If ssh decides to prompt you for a password, it will read it from /dev/tty instead of stdin.

Conceptually, /dev/tty is "the keyboard and text terminal". More or less.

Let's say my "terminal-file" of the current session is /dev/pts/1. In such a case, then what's the difference between "/dev/pts/1" and "/dev/tty"? And if they are basically the same, then why  "/dev/tty" is used instead of "/dev/pts/1"?

And:

/dev/tty is how a command like "ssh" can read your password even if its standard input comes from somewhere else

Let's say the standard input comes from somewhere else, so let's say we have:

FD 0 <- file
FD 1 -> /dev/pts/1
FD 2 -> /dev/pts/1

How I see it: the fact that the standard input comes from somewhere else doesn't mean that /dev/pts/1 can not be read? The password comes from the keyboard and /dev/pts/1 represents i.a. the keyboard, right? So I still don't see what exactly the purpose is of /dev/tty?

@noci: I know you know the answer, but I don't understand your explanation so I've made this post so maybe other people can explain it to me in a way that I understand it.
ASKER CERTIFIED SOLUTION
mccarl
IT Business Systems Analyst / Software Developer
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