CODE EXAMPLE FOR SHELL

run tmux on startup

# .bashrc
just above your aliases section

if command -v tmux &> /dev/null && [ -n "$PS1" ] && [[ ! "$TERM" =~ screen ]] && [[ ! "$TERM" =~ tmux ]] && [ -z "$TMUX" ]; then
  exec tmux
fi

# For more info | https://unix.stackexchange.com/questions/43601/how-can-i-set-my-default-shell-to-start-up-tmux