My .tmux.conf ( usable across multi-platforms including OS X | Linux | Cygwin )

.tmux.conf

set-option -g default-terminal "xterm-256color"
set-window-option -g xterm-keys on

run-shell "tmux setenv -g TMUX_VERSION $(tmux -V | cut -c 6-)"

setw -g mode-keys vi

unbind C-b

# remap prefix to Control + Space
set -g prefix C-Space

# bind 'C-Space C-Space' to type 'C-Space'
bind C-Space send-prefix

# set small delay for each command
set -sg escape-time 1

set -g display-panes-time 4000

bind \ split-window -h -c '#{pane_current_path}'
bind - split-window -v -c '#{pane_current_path}'

bind h select-pane -L
bind j select-pane -D
bind k select-pane -U
bind l select-pane -R

bind -r H resize-pane -L 5 
bind -r J resize-pane -D 5 
bind -r K resize-pane -U 5 
bind -r L resize-pane -R 5 

bind @ respawn-pane -k

bind C-b copy-mode

bind -T copy-mode-vi v send-keys -X begin-selection

# To prevent some garbage characters from being printed to screen after copying or selecting something
# See https://www.reddit.com/r/tmux/comments/2xgrf8/garbage_characters_printed_to_screen_after_a/
set -g set-clipboard off
setw -g mouse on
#set -g mouse-select-pane on
#set -g mouse-resize-pane on
#set -g mouse-select-window on

# set color of active pane
if-shell -b '[ `echo "$(tmux -V | grep -o "[2-9]\.[0-9]\+") >= 2.8" | bc` -eq 1 ]' \
    'set -g pane-border-style bg=black,fg=white; set -g pane-active-border-style bg=black,fg=green' \
    'set -g pane-border-fg colour235; set -g pane-border-bg black; set -g pane-active-border-fg green; set -g pane-active-border-bg black'

# color status bar
#set -g status-bg colour235
#set -g status-fg white

# disable status bar
set -g status off

if-shell 'uname | grep -q Darwin' \
    'source-file ~/.tmux.conf.osx' \
    'if-shell "uname | grep -q CYGWIN" "source-file ~/.tmux.conf.cygwin" "source-file ~/.tmux.conf.linux"'

.tmux.conf.cygwin

# Copy the current buffer to system clipboard
bind C-c run "tmux save-buffer - | cat >/dev/clipboard" \

# Copy system clipboard to the current buffer and then paste the content
bind C-v run "cat /dev/clipboard | tmux load-buffer - && tmux paste-buffer" \

# Copy selection using a vi-like command; also copy it to system clipboard
if-shell -b '[ `echo "$(tmux -V | grep -o "[2-9]\.[0-9]\+") >= 2.4" | bc` -eq 1 ]' \
    'bind -T copy-mode-vi y send-keys -X copy-pipe "cat >/dev/clipboard"' \
    'bind -t vi-copy y copy-pipe "cat >/dev/clipboard"'
    

.tmux.conf.linux

# If you prefer xclip, use : 
# bind C-c run "tmux save-buffer - | xclip -i -sel clipboard"
# bind C-v run "tmux set-buffer \"$(xclip -o -sel clipboard)\"; tmux paste-buffer" 

# Copy the current buffer to system clipboard
bind C-c run "tmux save-buffer - | xsel --clipboard --input"

# Copy system clipboard to the current buffer and then paste the content
bind C-v run "xsel --clipboard --output | tmux load-buffer - && tmux paste-buffer"

# Copy selection using a vi-like command; also copy it to system clipboard
if-shell -b '[ `echo "$(tmux -V | grep -o "[2-9]\.[0-9]\+") >= 2.4" | bc` -eq 1 ]' \
    'bind -T copy-mode-vi y send-keys -X copy-pipe "cat | xsel --clipboard --input"' \
    'bind -t vi-copy y copy-pipe "cat | xsel --clipboard --input"'

.tmux.conf.osx

# Copy selection using a vi-like command; also copy it to system clipboard
bind -T copy-mode-vi y send-keys -X copy-pipe "pbcopy"

please include which tmux version it's compatible with

This configuration is compatible with tmux 2.2

Any updates for version 2.9A?

Configuration is now compatible with 2.9A. Also it'll work with older versions. (but not too older)

And it works with Windows Subsystem for Linux on Windows 10.

Thanks!

-if-shell -b '[ "$(echo "${TMUX_VERSION:0:3} >= 2.8" | bc)" = 1 ]' \
+if-shell -b '[ `echo "$(tmux -V | grep -o "[2-9]\.[0-9]\+") >= 2.8" | bc` -eq 1 ]' \

Shell syntax for if-shell should conform to POSIX on some system. (E.g., Ubuntu)