Start a process on a different tty

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.

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.

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...)