To setup ‘v’ and ‘y’/Enter for begin-selection and copy in newer version of tmux (2.4 and later) in ubuntu, here’s what I ended up with:
# setup 'v' to begin selection as in Vim
bind-key -T copy-mode-vi 'v' send -X begin-selection
bind-key -T copy-mode-vi 'y' send -X copy-pipe "xclip -i -sel p -f | xclip -i -sel c" \; display-message "copied to system clipboard"
# Update default binding of `Enter` to also use copy-selection
unbind -T copy-mode-vi Enter
bind-key -T copy-mode-vi Enter send -X copy-pipe "xclip -i -sel p -f | xclip -i -sel c" \; display-message "copied to system clipboard"