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Date: Mon, 10 Jul 2006 21:07:46 -0400
From: "Albert Cahalan" <acahalan@gmail.com>
To: "Jan Engelhardt" <jengelh@linux01.gwdg.de>
Subject: Re: Opinions on removing /proc/tty?
Cc: ray-gmail@madrabbit.org, "Jon Smirl" <jonsmirl@gmail.com>,
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On 7/10/06, Jan Engelhardt <jengelh@linux01.gwdg.de> wrote:
> >> > Just do /proc/*/tty links and all will be good. This even
> >> > handles the case of two different names for the same dev_t.
> >> >
> >> Is this for the controlling tty? Then it should be ctty.
> >
> > Eeeew, an extra byte so it can look ugly.
> > What other special tty is there?
> >
> Any fd, for that matter.
>
> 00:09 shanghai:/dev/shm > ls -l /proc/$$/fd
> total 4
> dr-x------  2 jengelh users  0 Jul 11 00:16 .
> dr-xr-xr-x  5 jengelh root   0 Jul 11 00:04 ..
> lrwx------  1 jengelh users 64 Jul 11 00:16 0 -> /dev/pts/2
> lrwx------  1 jengelh users 64 Jul 11 00:16 1 -> /dev/pts/2
> lrwx------  1 jengelh users 64 Jul 11 00:16 2 -> /dev/pts/2
> lrwx------  1 jengelh users 64 Jul 11 00:16 255 -> /dev/pts/2
> and CTTY is /dev/tty1.
>
> So what would /proc/$$/tty - ambiguous name - point to, the normal (attached)
> or the ctty? Not to mention exotic, yet possible things

The tty is obviously one and the same as:

a. "tty" in the kernel's struct signal_struct
b. the "TTY" or "TT" reported by ps.
c. what "/dev/tty" refers to

Any other tty is not "the tty". Exactly one tty is special.

On any of Linux, MacOS, Solaris, NetBSD, OpenBSD:

$ ls /dev/tty /dev/ctty
ls: /dev/ctty: No such file or directory
/dev/tty

Lord only knows why FreeBSD has both.
Unlike Linux, they don't supply a man page.
On a Linux system, "man 4 tty" is useful.
On a Solaris system, "man -s 7d tty" is useful.