Using the same clipboard (x-clipboard) for ubuntu and mac os X in the same script for emacs.

use_share_x-clipboard_on_emacs_for_ubuntu_and_mac_os_x.lisp

;;;;; Add in your ~/.emacs.d/init.el

;;;; Clipboard for ubuntu
(defun copy-from-ubuntu (text &optional push)
  (interactive)
  (if (display-graphic-p)
      (progn
        (message "Yanked region to x-clipboard!")
        (call-interactively 'clipboard-kill-ring-save)
        )
    (if (region-active-p)
        (progn
          (shell-command-on-region (region-beginning) (region-end) "xsel -i -b")
          (message "Yanked region to clipboard!")
          (deactivate-mark))
      (message "No region active; can't yank to clipboard!")))
    )

(defun paste-to-ubuntu ()
  (interactive)
  (if (display-graphic-p)
      (progn
        (clipboard-yank)
        (message "graphics active")
        )
    (insert (shell-command-to-string "xsel -o -b"))
    )
  )

;;;;; Clipboard Mac OS X
(defun copy-from-osx ()
  (shell-command-to-string "pbpaste"))
(defun paste-to-osx (text &optional push)
  (let ((process-connection-type nil))
    (let ((proc (start-process "pbcopy" "*Messages*" "pbcopy")))
      (process-send-string proc text)
      (process-send-eof proc))))

(if (equal (shell-command-to-string "uname") "Darwin\n")
  (progn
    ;;;;; Clipboard Mac OS X
    (setq interprogram-cut-function 'paste-to-osx)
    (setq interprogram-paste-function 'copy-from-osx))
  (progn
    ;;;;; Clipboard UBUNTU
    (setq interprogram-cut-function 'copy-from-ubuntu)
    (setq interprogram-paste-function 'paste-to-ubuntu)))

In ubuntu you must install

$ sudo apt-get install xsel

It works but doesn't disable the "kill ring".

Debugger entered--Lisp error: (error "Kill ring is empty")
  signal(error ("Kill ring is empty"))
  error("Kill ring is empty")
  current-kill(0)
  yank(nil)
   funcall-interactively(yank nil)
  call-interactively(yank nil nil)
  command-execute(yank)