[chirayuk]

I believe tmux 1.8 supports this use case.

From the manpage (for new-session):  If -t is given, the new session is grouped with target-session.  This means they share the same set of windows - all windows from target-session are linked to the new session and any subsequent new windows or windows being closed are applied to both sessions.  The current and previous window and any session options remain independent and either session may be killed without affecting the other.

[Sodel]

I've started running tmux in all my terminals automatically, and conveniently sharing a "master" session between them all.

Instead of running tmux directly, I have a small script which creates a session named TMUX-MASTER if it doesn't already exist, and immediately detaches it. All the clients that I actually interact with are created separately and automatically grouped with the TMUX-MASTER session.

To prevent my system from being clogged by dozens of detached client sessions, I rebound prefix+d to kill-session, killing the client session but leaving my TMUX-MASTER session untouched. Closing terminals while running these client sessions, however, still leaves my system cluttered with dormant client sessions.

I'd like to see if a "ephemeral" option (it'd need a better name) could easily be added to new-session, which would cause the created session to just die when it's told to detach, or receives the HUP signal. It'd simplify things a bit.