Editing X Window System (section)

===Network===
[[File:X11 ssh tunnelling.png|right|250px|thumb|Example of tunnelling an X11 application over SSH]]

An X client cannot generally be detached from one server and reattached to another unless its code specifically provides for it ([[Emacs]] is one of the few common programs with this ability). As such, moving an entire session from one X server to another is generally not possible. However, approaches like [[Virtual Network Computing]] (VNC), [[NX technology|NX]] and [[Xpra]] allow a virtual session to be reached from different X servers (in a manner similar to [[GNU Screen]] in relation to terminals), and other applications and toolkits provide related facilities.<ref>{{cite web |url-status=dead |url=http://icie.cs.byu.edu/cs656/Papers/Gettys.pdf |title=SNAP Computing and the X Window System |archive-url=https://web.archive.org/web/20100626203344/http://icie.cs.byu.edu/cs656/Papers/Gettys.pdf |archive-date=26 June 2010 |first1=James |last1=Gettys |at=4.6 |website=Interactive Computing Everywhere }}</ref> Workarounds like [[x11vnc]] (''VNC :0 viewers''), Xpra's shadow mode and NX's nxagent shadow mode also exist to make the current X-server screen available. This ability allows the user interface (mouse, keyboard, monitor) of a running application to be switched from one location to another without stopping and restarting the application.

Network traffic between an X server and remote X clients is not encrypted by default. An attacker with a [[packet sniffer]] can intercept it, making it possible to view anything displayed to or sent from the user's screen. The most common way to encrypt X traffic is to establish a [[Secure Shell]] (SSH) tunnel for communication.

Like all [[thin client]]s, when using X across a network, [[Bandwidth (computing)|bandwidth]] limitations can impede the use of [[bitmap]]-intensive applications that require rapidly updating large portions of the screen with low latency, such as 3D animation or photo editing. Even a relatively small ''uncompressed'' 640×480×24&nbsp;bit 30&nbsp;fps video stream (~211&nbsp;Mbit/s) can easily outstrip the bandwidth of a 100&nbsp;Mbit/s network for a single client. In contrast, modern versions of X generally have extensions such as [[Mesa (computer graphics)|Mesa]] allowing local display of a local program's graphics to be optimized to bypass the network model and directly control the video card, for use with full-screen video, rendered 3D applications, and other such applications.