Cygwin tmux: “failed to connect to server: No error”

I did some digging and found the answer for myself. Well, the way I have found to accomplish my gaol is not elegant, but it will work to get the job done.

First, you need to have the "set-titles" option turned on in your .tmux.conf file. As well as the appropriate title string:

set -g set-titles on
set -g set-titles-string '#T'

However, if you implement this, you will immediately notice that it doesn't work. The problem is that this only sends the title string up stream if it starts in an xterm variant (tmux/screen TERM variable is "screen*"). So, when starting a nested tmux session, you must fool the terminal by resetting the variable. The following example will keep the TERM suffix (e.g. "-256color").

TEMP_TERM=$TERM
TEMP_TERM_SUFFIX=${TERM#$(echo $TERM | cut -f 1 -d'-')}
TERM="xterm${TEMP_TERM_SUFFIX}"

I am not sure if it matters, but I think it is smart to reset TERM back after closing tmux (so save it into a temp variable). Using this, a simple shell script can be made to open a nested tmux session that sends the #T title variable upstream to it's parent sessions.

This all works, but is somewhat of a pain considering that work must be done to ensure infinite nesting loops aren't created in the event that we automatically start our shell up in tmux. If anyone has a better solution I would love to here it as well!

I had this same problem. It was caused by having set-option -g default-command "reattach-to-user-namespace -l zsh" in my .tmux.conf without having reattach-to-user-namespace installed.

The fix was to install "reattach-to-user-namespace" via Homebrew (brew install reattach-to-user-namespace)