The X Window System uses its own clipboard system that is distinct from the clipboard system used by Windows. Copying and pasting text between these two clipboard systems requires a clipboard integration program that watches for updates to either clipboard and copies data between them when either one is updated. Cygwin/X has an internal clipboard integration program that is enabled by default.
The clipboard integration monitors the X PRIMARY (selected/highlighted text) and CLIBPOARD (cut/copied text) selections for changes in ownership, and makes the contents of the most recent one to change available to paste from the Windows clipboard. It also monitors the contents of the Windows clipboard for changes, taking ownership of the PRIMARY and CLIPBOARD selections, and making the contents of the Windows clipboard available in them.
Note: Some X clients, notably ones written in Tcl/Tk, do not re-assert ownership of the PRIMARY selection or update it's timestamp when it's contents change, which currently prevents the clipboard integration program from correctly noticing that the PRIMARY selection's contents have changed.
Note: With some X clients, it may be inconvenient that updating the PRIMARY selection causes that to overwrite the Windows clipboard contents you were just about to paste, so monitoring of the X PRIMARY selection can be disabled using the
-noprimaryoption, or temporarily using the "Clipboard may use PRIMARY selection" toggle on the notification area icon menu.
See the Section called Command line parameters in Chapter 4
for more information on the -[no]clipboard and
-[no]primary command-line options.