XWN740 X-Windows Configuring and Using Using VNC (Chapter 14: Pages )‏

Agenda Using VNC: Purpose Using VNC Running VNC Server Running VNC Viewer Running VNC within SSH Tunnel Bypassing a firewall

VNC VNC - Purpose VNC stands for Virtual Network Computer and is an open source technology that provides a low-bandwidth, platform-independent remote display service. VNC is an amazingly versatile tool. It can be started by non-root users, or configured to start automatically on demand; it can be accessed on a wide range of OS platforms using a native viewer or a portable Java or.Net applet..

VNC USING VNC vncserver RealVNC and TightVNC provide a script named vncserver. This script may be run by a regular user, and it starts Xvnc on the local sytem with a preset group of clients. The first available X server number will be used for both the X and VNC display numbers. Since clients are started automatically, the VNC session is always password-protected. This program is basically the VNC equivalent of the startx command.

VNC USING VNC Using Xvnc Xvnc is a combined X server and VNC server. It may be started on a command line like any other X server. This gives you the opportunity to select the specific clients that will be started; it also enables you to choose different VNC and X display numbers, enable or disable the built- in web server, and control the use of passwords. Running the command vncserver is a wrapper for Xvnc which will prompt the user for a password.

VNC USING VNC Starting Xvnc from command line vncpasswd ~/myvncpasswd # (type & verify new password)‏ Xvnc -query [server-ip] -once – rfbauth ~/myvncpasswd Starting vncserver from command line vncserver

VNC USING VNC Starting Xvnc from /etc/inittab In the same way that character-based logins are run on VTs 1-6, and an X server is started on VT7, it's possible to configure /etc/inittab to start standing X servers at boot time. This provides an easy way for remote users to log in to the system and to have a persistent connection which will remain available across disconnections and re- connections. When used in this way, Xvnc is usually configured to issue an XDCMP query (often to localhost) and VNC passwords are used.

VNC Using VNC Starting Xvnc from Inetd The inetd superserver is used to start services on demand. When used with Xvnc, this provides the opportunity to start as many servers as system resources permit without pre-configuring a set number of standing servers and without wasting any resources on servers that are not needed.

VNC USING VNC VNC Viewers Binary VNC viewers are available for many platforms, including PDAs and cell phones. The Java VNC viewer is designed to be embedded into a web page as an applet. Due to the standard Java applet security restrictions, the embedded applet can only contact the server from which the web page was served; for convenience, Xvnc contains a mini webserver for this purpose. However, this web server cannot be used when Xvnc is started by Inetd, so a separate web server is required when using Inetd and the Java applet.

VNC USING VNC Starting viewer from command line Vncviewer [ip-address]:display Starting viewer from Java-enable Browser Firefox (assuming that server is running display 4... i.e display number )‏

VNC Running VNC (Tunneling with SSH)‏ The minimal security features provided by VNC can be greatly enhanced by tunneling the RFB protocol through SSH. Most native clients support the use of SSH through the -via command-line argument, which configures an SSH tunnel automatically. For example: vncviewer -via

VNC Running VNC (Bypassing a Firewall)‏ Firewalls can pose a problem when using VNC. The simplest and most secure method to solve this problem is through SSH tunneling. First, run the vncviewer to provide a reverse connection: vncviewer -listen Then, start the vncserver to broadcast on port 5500: vncconnect -display :1 [IP-address]:5500