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After about an hour of Googling this, I can't believe nobody has actually asked this question before...

So I've got a script running on TTY1. How do I make that script launch some arbitrary program on TTY2?

  • I found tty, which tells you which TTY you're currently on.
  • I found writevt, which writes a single line of text onto a different TTY.
  • I found chvt, which changes which TTY is currently displayed.

I don't want to display TTY2. I just want the main script to continue executing normally, but if I manually switch to TTY2 I can interact with the second program.

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  • From TTY1, Have you tried [command] > /dev/tty2 (you have to already logged-in to tty2)?
    – Pandya
    Nov 26, 2014 at 13:54
  • 1
    this could be a XYproblem ... what are you trying to achieve? what is the overall goal? Nov 27, 2014 at 7:48

5 Answers 5

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setsid sh -c 'exec command <> /dev/tty2 >&0 2>&1'

As long as nothing else is using the other TTY (/dev/tty2 in this example), this should work. This includes a getty process that may be waiting for someone to login; having more than one process reading its input from a TTY will lead to unexpected results.

setsid takes care of starting the command in a new session.

Note that command will have to take care of setting the stty settings correctly, e.g. turn on "cooked mode" and onlcr so that outputting a newline will add a carriage return, etc.

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  • 3
    That is not correct. You mix up the controlling terminal with /dev/stdin, /dev/stdout, and /dev/stderr. ps easily shows that command does not have a controlling terminal at all in your case. Nov 26, 2014 at 16:49
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    @HaukeLaging, a session leader takes control of a terminal as soon as it opens it. The problem was that the terminal device was not open by the session leader. Should be fixed now. Nov 26, 2014 at 19:30
  • @StéphaneChazelas I tested with sleep 1000 and it still doesn't work here. I used a pseudo tty, though (shouldn't make a difference, I guess). Nov 26, 2014 at 19:38
  • @HaukeLaging How exactly did you do it? Did that terminal not have a controlling session already (the As long as nothing else is using the other TTY part)? Nov 26, 2014 at 19:41
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    @StéphaneChazelas I ran setsid sh -c 'exec sleep 1000 <>/dev/pts/4 >&0 2>&1' in a terminal emulator window. /dev/pts/4 is another terminal emulator window (same user, with bash running). Nov 26, 2014 at 19:45
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On the second tty there will be normally a program running, either some login program or some shell like bash. If you want interaction you either would have to replace the login program with yours, or tell a shell to run the program as if the program was started from the commandline.

A more simple solution, IMO, would be to start a tmux session after logging into the second screen and then use:

tmux send yourcommand ENTER

to start the program in the tmux session which will display after you switch to the second terminal.

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I just made a discovery:

How can I launch applications from 2 ttys on launch?

One of the comments mentions something called openvt. This command appears to do the exact thing I'm after!

http://linux.about.com/library/cmd/blcmdl1_openvt.htm

Unless anyone knows different, I think this is probably the "correct" way to do this.

(I just tried it, and it seems to work fine - even though getty is running, it picks the next unused terminal. I guess VTs don't get "opened" until you switch to one to try to log in...)

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4

i start a new graphical session on the vt5 with the follow command

xinit "/usr/bin/<binary_executable>" -- :1 vt5

for example :

xinit "/usr/bin/playonlinux" -- :1 vt5

If you want to launch a graphical application on already active graphical session you can do with :

DISPLAY=:0 "/usr/bin/playonlinux"
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  • Thanks! this is exactly what I was trying to figure out (DISPLAY=:0)
    – Don
    Jan 2, 2022 at 4:32
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start bash on different tty:

setsid agetty --autologin root  --noclear 19200 ttyS1 linux

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