Why does tmux bind externally accessible ports?

Solution 1:

It is tmux and it is a Unix socket. Tmux apparently uses server sockets to allow for independent tmux servers to be run. man tmux

Run tmux with no flags

tmux

$ ss -l |grep tmux
u_str  LISTEN     0      128    /tmp/tmux-1000/default 62749                 * 0

Then run tmux with -S /tmp/tmux.sock and see that the change in the socket path.

$ ss -l |grep tmux
u_str  LISTEN     0      128    /tmp/tmux.sock 62765                 * 0

Note, It is not TCP. This can be seen from using the flags -t (tcp) and -l (listening)

$ ss -tl
(returns no lines but the headers)

Solution 2:

are you using tcsh? https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=204429 has a similar-ish problem where starting tmux on tcsh results in dns queries.