Pane Title in Tmux

tmux limits the dimensions of a window to the smallest of each dimension across all the sessions to which the window is attached. If it did not do this there would be no sensible way to display the whole window area for all the attached clients.

The easiest thing to do is to detach any other clients from the sessions when you attach:

tmux attach -d

Alternately, you can move any other clients to a different session before attaching to the session:

takeover() {
    # create a temporary session that displays the "how to go back" message
    tmp='takeover temp session'
    if ! tmux has-session -t "$tmp"; then
        tmux new-session -d -s "$tmp"
        tmux set-option -t "$tmp" set-remain-on-exit on
        tmux new-window -kt "$tmp":0 \
            'echo "Use Prefix + L (i.e. ^B L) to return to session."'
    fi

    # switch any clients attached to the target session to the temp session
    session="$1"
    for client in $(tmux list-clients -t "$session" | cut -f 1 -d :); do
        tmux switch-client -c "$client" -t "$tmp"
    done

    # attach to the target session
    tmux attach -t "$session"
}
takeover 'original session' # or the session number if you do not name sessions

The screen will shrink again if a smaller client switches to the session.

There is also a variation where you only "take over" the window (link the window into a new session, set aggressive-resize, and switch any other sessions that have that window active to some other window), but it is harder to script in the general case (and different to “exit” since you would want to unlink the window or kill the session instead of just detaching from the session).

Here is one way to have the tmux pane title updated every time you execute a command in BASH. Put code like the below in ~/.bashrc:

case ${TERM} in

    screen*)

        # user command to change default pane title on demand
        function title { TMUX_PANE_TITLE="$*"; }

        # function that performs the title update (invoked as PROMPT_COMMAND)
        function update_title { printf "\033]2;%s\033\\" "${1:-$TMUX_PANE_TITLE}"; }

        # default pane title is the name of the current process (i.e. 'bash')
        TMUX_PANE_TITLE=$(ps -o comm $$ | tail -1)

        # Reset title to the default before displaying the command prompt
        PROMPT_COMMAND=${PROMPT_COMMAND:+$PROMPT_COMMAND; }'update_title'   

        # Update title before executing a command: set it to the command
        trap 'update_title "$BASH_COMMAND"' DEBUG

        ;;

        ... other cases for different terminals ...

esac

}

The function update_title prints the escape sequence that changes the tmux pane title. It sets the pane title to the default (the value of $TMUX_PANE_TITLE) or to whatever is given as an argument.

The function title is for end-user convenience: it changes the value of the default title in $TMUX_PANE_TITLE. The end user can at any time change the title to whever they want by doing:

$ title my new pane title

The initial title is set to the name of the running shell (i.e. 'bash').

Bash executes anything in $PROMPT_COMMAND prior to displaying a prompt. This is set so that the update_title function gets executed before every prompt to set the prompt to the default title.

The trap causes Bash to execute $BASH_COMMAND before executing any command. It is set so that the update_title function gets executed before every command to set the prompt to the text of that command.

Other notes

• while working this out, I discovered that set -o functrace or set -T (as described by person linked to in the question) causes RVM to break. The reason for it being suggested was to allow prompts to change in subshells but the lack of this wasn't a problem to me.

• To get the initial title, I wanted to use the more succinct ps -ho comm $$ but this seemed to not work inside tmux with the above in place. I am not sure why so opted for something else that did work.