My tmux started to behave in a strange way, briefly.
Today I noticed that my tmux session does not start with a bash shell but instead it starts with ?(no idea). What I can see is just a dollar $.
Then if I try to call bash with bash it returns
sessions should be nested with care, unset $TMUX to force.

I wanted to add a default-shell for tmux in the ~/.tmux.conf file, but it doesn't exist and if I create it tmux seems not seeing it.
echo $0? – user4556274 May 09 '17 at 12:59sh– Peter May 09 '17 at 15:05