ssh cómo iniciar un script fuera de la sesión

ssh into the remote machine
start tmux by typing tmux into the shell
start the process you want inside the started tmux session
leave/detach the tmux session by typing Ctrl+b and then d
You can now safely log off from the remote machine, 
your process will keep running inside tmux. 
When you come back again and want to check the status 
of your process you can use tmux attach to attach to your tmux session.
ofroog