To enable clipboard sharing between tightvnc server and client,

First install autocutsel.

Now, you need to modify the file ~/.vnc/xstartup.

Add the following lines to it:

export XKL_XMODMAP_DISABLE=1
autocutsel -fork

The file finally looks like this:

#!/bin/sh
xrdb $HOME/.Xresources
xsetroot -solid grey
export XKL_XMODMAP_DISABLE=1
autocutsel -fork
/etc/X11/Xsession

You may need to install autocutsel

In Ubuntu (if that’s your client OS), you need an additional step in the client side. Press F8 in the vnc viewer, and choose Clipboard(Local->Remote).