VNC Server for Windows

System Requirements


  • System hardware meeting OS requirements
  • Windows-compatible graphics card
  • Windows-compatible network card
  • TCP/IP v4 network stack
  • Windows 981
    or Windows Me1
    or Windows NT 4.0 Workstation / Server2
    or Windows 2000 Professional / Server
    or Windows XP Professional / Home3
    or Windows 2003 Server3


  1. These platforms do not support secure settings
  2. Service Pack 3, 4, 5 or 6a is required on these platforms
  3. If Fast User Switching or Remote Desktop are used, then VNC Server will connect session zero to the console in order to allow it to be accessed. Other sessions cannot be accessed by VNC Open 4.1 Server.


VNC Server for Windows is installed as an optional component of the setup package. If VNC Server has been installed then a number of icons will be created for it under the Start Menu, at the location specified during installation (usually RealVNC).

VNC Server for Windows is designed to run either in User-Mode, as a personal per-user server, or in Service-Mode, as a system service available whether or not there is a user logged in.

The logged-on user can also choose to run their own personal User-Mode server alongside an existing Service-Mode server installed on the machine, provided that the two servers are configured to operate on different network port numbers.

Upgrading from VNC Open 4.0

VNC Server 4.1 retains full compatibility with VNC Server 4.0, with respect both to command-line parameters and to registry configuration options. When installed on a system that has already been fully configured for VNC Server 4.0, VNC Server 4.1 will use the existing settings, without the need for reconfiguration.

Using VNC Server in User-Mode

If you are just trying out VNC, or wish to provide access to your desktop infrequently for support or collaboration purposes, then you may find it best to run VNC Server in User-Mode.

During the installation, leave the tickboxes which refer to the VNC Server System Service unticked, to prevent VNC Server being installed in Service-Mode on your system.

winvnc4 startmenu

When you want to use VNC Server, go to the VNC Server (User-Mode) program group (usually found under RealVNC in the Start Menu), and click on Run VNC Server. The VNC Server icon will appear in the system tray, to indicate that VNC Server is running.

winvnc4 traymenu

At this point, you probably want to configure your personal VNC Server settings for User-Mode. Right-click on the tray icon and select Options..., change the settings you want and click Apply or Ok. Note that you must at least configure the Authentication tab, otherwise you won't be able to connect in to your server - this is deliberately the case, to avoid accidentally opening up your computer to attacks.

When you are finished with VNC Server, simply select Close VNC Server from the tray icon's menu.

Using VNC Server in Service-Mode

If you intend to use VNC to provide remote access to a computer, you will probably prefer to install VNC Server in Service-Mode. In Service-Mode, VNC Server can allow remote connections even while the computer is locked or logged off. The server is configured once, rather than per-user, and the settings are secured if the host platform supports it.

During the installation, tick each of the boxes which refer to the VNC Server System Service. This will cause the installer to present the VNC Server Options dialog, and to register and run the VNC Server Service.

Note that you must at least configure the Authentication tab, otherwise you won't be able to connect in to your server - this is deliberately the case, to avoid accidentally opening up your computer to attacks.

At this point, your VNC Server is running and you should be able to connect to it from a connected computer using VNC Viewer.

If you need to reconfigure or stop your Service-Mode server, you will find links in the VNC Server (Service-Mode) program group of the Start Menu to achieve this. The VNC Server Properties dialog can also be accessed by right clicking on the VNC Server (Service-Mode) tray icon and selecting the Options... menu item.

Configuring VNC Server

VNC Server provides a number of options allowing its behaviour to be tailored to your needs. These are usually configured via the Options... dialog, although they can also be specified directly on the command-line of the WinVNC4 executable if required.

The Options... dialog consists of a number of pages of options, grouped according to their function. The following documentation describes each option and the equivalent command-line parameters.

When the Ok or Apply buttons of the Options... dialog are pressed, any changed settings are saved to the registry. Unless otherwise specified, changed settings take effect immediately.


winvnc4 connections

Accept connections on port
PortNumber=(port number)

If this option is ticked and the port number is non zero then VNC Server accepts incoming connection requests from clients on a particular TCP port. The standard VNC Display numbers, 0-99, correspond to TCP ports 5900-5999. VNC Server will accept connections on port number 5900 by default, which equates to VNC display number 0 (zero). The port number for VNC Server to use can be set to any other available port number, even ones outside the 5900-5999 range.

Disconnect idle clients after

An idle client is one which has transmitted no keyboard or pointer events for more than a certain length of time. The VNC Server can be configured with a threshold, expressed in seconds, after which idle clients will be disconnected to conserve resources. If the threshold specified is zero seconds then connections will never timeout. The default idle timeout is one hour.

Note that pointer and keyboard events received from clients will prevent their connection timing out even if the VNC Server is configured to otherwise ignore those events (see below).

Serve Java viewer via HTTP on port
HTTPPortNumber=(port number)

If this option is ticked and the port number specified is non-zero then VNC Server will accept incoming HTTP requests, allowing the Java VNC Viewer to be downloaded by a Java-aware web browser. The Options... dialog will attempt to adjust the HTTP port to match changes made to the VNC port number.

Note that the HTTP port number cannot be set to the same value as that used for incoming VNC connections.

Only accept connections from the local machine

The LocalHost option tells VNC Server to only accept incoming connections from Viewers running on the local host computer. This is only normally used when connections are to tunnelled through a custom transport (e.g. serial line, custom wireless, etc) and will therefore appear to the TCP stack to originate from the local host. If VNC Server is configured to accept connections only via local loopback then the Hosts option is ignored.

Access Control

VNC Server can filter incoming connection attempts based upon the apparent IP addresses of their originators. Which IP addresses are allowed to connect and which are not is determined by the Hosts pattern. The pattern consists of a comma-separated list of IP address specifications, prefixed by an action. Each specification starts with an action, gives an IP address, and a subnet-style mask. The first specification to match the address of the new connection determines the action that will performed.

Available actions are:

  • +: Accept the connection
  • ?: Query the local user to accept the connection.
    See also the QueryConnect Authentication option.
  • -: Reject the connection.

e.g. Hosts=+,+,-

The pattern given above allows the computer with address to connect, as well as any computer in the 192.168.1 subnet. All other connections are rejected by the - term, which is actually redundant in this case - a connection will always be rejected if it doesn't match anything in the Hosts pattern.

Note that IP addresses and masks are specified in Type-A (xxx.yyyyyyyyy), Type-B (xxx.yyy.zzzzzz) or Type-C (xxx.yyy.zzz.www) form. The specification 192.168 will therefore be interpreted as rather than as one might expect.

The Hosts pattern can be edited more easily through the Access Control interface, which allows IP address specifications to be edited individually and moved up (to match first) or down (to match last) the list.


winvnc4 authentication

The Authentication page allows you to configure the required mode of authentication and level of security of VNC connections. VNC Open Server for Windows supports unauthenticated connections and classic VNC Password Authentication.

No Authentication

If your VNC Server is operating in a protected environment, such as a secure LAN or firewall-protected network, then you may wish to configure VNC Server to accept connections without requiring a username or password to be specified.

We advise extreme caution when disabling authentication. Do not disable it unless you are absolutely sure that the host network is completely secure.

VNC Password Authentication

VNC Password Authentication allows a single password of up to 8 characters to be stored by VNC Server, which remote users must supply when prompted in order to authenticate.

The password to use can be configured by selecting Configure and typing the new password twice. On platforms which support it, the password (and all other configuration options) are protected using native operating system security methods, so that the password cannot be read or tampered with by other users.

NT Logon Authentication

NT Logon Authentication is not available in VNC Open.

Encryption: Always Off

Encryption is not available in VNC Open.

Prompt local user to accept connections

By default, VNC Server allows Viewers to connect as long as the correct username and password are supplied. QueryConnect allows an extra level of protection to be applied, requiring a local user to explicitly accept incoming connections.

When QueryConnect is enabled, incoming connections are first authenticated in the normal way. If the user authenticates successfully then a dialog is presented on the server's desktop, displaying the IP address and username of the incoming connection, and requiring a local user to accept the connection.

If the user does not accept the connection within a specified timeout then it is rejected. If an incoming connection requiring acceptance by the local user is received while an earlier connection is being queried then the second connection is automatically rejected, for security reasons.

Connections from specific hosts or subnets can be configured to be queried via the Hosts configuration setting.

Only prompt when there is a user logged on

This option affects the behaviour of the QueryConnect option, if enabled. If this option is set then the local user will only be prompted to accept the incoming connection if they are logged in. If this option is not set then the local user will always be prompted, regardless of whether or not they are logged in.

Note that it is not possible to reliably detect whether or not a user is logged in on some older Windows platforms. On these platforms, this option will err on the side of security and always prompt the local user.


If QueryConnect is enabled then the Query Connection dialog will be displayed by default for ten seconds before automatically rejecting the connection. The timeout value can be modified by setting QueryConnectTimeout accordingly.


winvnc4 inputs

Accept pointer events from clients

If this option is unticked then incoming pointer movements from all clients will be ignored, preventing any remote VNC Viewer from affecting the pointer of the VNC Server's desktop. This can be used to configure a server to become effectively view-only.

Note that a client will still be deemed active for the purposes of the IdleTimeout setting if it is sending pointer events to the server, whether or not they are accepted.

Accept keyboard events from clients

If this option is unticked then incoming keystrokes from all clients will be ignored, preventing any remote VNC Viewer from typing into the VNC Server's desktop. This can be used to configure a server to become effectively view-only.

Note that a client will still be deemed active for the purposes of the IdleTimeout setting if it is sending keyboard events to the server, whether or not they are accepted.

Accept clipboard updates from clients

If this option is unticked then incoming clipboard updates will be ignored from all clients. This option should be used when making a VNC Server effectively view-only, but may also prove useful to prevent clipboard changes made by clients from overriding the VNC Server's local clipboard when this would be undesirable or confusing.

Send clipboard updates to clients

This option, if unticked, prevents the VNC Server from informing clients of changes to its local clipboard contents. This can be useful when untrusted clients are to be allowed to connect to the VNC Server, since it prevents any private data being accidentally leaked via the clipboard.

Allow input events to affect the screen-saver

This option determines whether keyboard and mouse events received from VNC Viewers can cause the screen-saver to be hidden. This option is actually a system-wide setting and is not implemented by VNC Server itself, so there is no equivalent command-line option. Some older Win32 platforms do not support this option. It is recommended that this check-box be ticked, so that the screen-saver can be disabled by VNC Viewer input.

Disable local inputs while server is in use

The mouse and keyboard physically attached to the server computer can be disabled for the duration of a remote connection, preventing local users from interacting with the computer.


winvnc4 sharing

Always treat new connections as shared

If this option is set then all incoming connections will be treated as shared, and thus not disconnect any existing connections, regardless of whether the connecting VNC Viewer requested that the connection be shared.

Never treat new connections as shared

If this option is set then all incoming connections will be treated as non-shared. VNC Server will therefore either disconnect any existing connections, or refuse the incoming connection, depending on whether non-shared connections are configured to replace existing ones (see below).

Use client's preferred sharing setting
AlwaysShared=false, NeverShared=false

When connecting, VNC Viewer specifies whether the connection should be shared or non-shared. If this setting is configured then the VNC Viewer's preference will be respected.

Non-shared connections replace existing ones

If an incoming connection is to be shared (either by choice or because AlwaysShared is set) then existing connections remain active. If a connection is non-shared (either by choice or because NeverShared is set) then either the new connection must be rejected, or existing clients disconnected.

If this setting is configured then existing clients will be disconnected when a new non-shared connection is made. Otherwise, they will remain, and the new connection will fail.


winvnc4 desktop

While connected

Decorations such as wallpaper or font smoothing effects can make it harder for VNC Server to compress graphical data for trasmission to viewers. For viewers connected over slower networks, this can significantly degrade the apparent performance of the server. VNC Server can therefore simplify the desktop in several ways, to improve performance.

Remove wallpaper

This option causes VNC Server to remove any standard wallpaper bitmap that is set, as well as to disable Active Desktop components.

Remove background pattern

This option causes VNC Server to set the desktop background to a plain pattern while conenctions are active.

Disable user interface effects

This option causes VNC Server to disable desktop decorations such as font smoothing, window titlebar shading, menu animation, and so on.

When last client disconnects

These options are used to ensure that if VNC connections to a server are closed because of a network error, idle timeout, or even deliberately, then the computer will be left in as secure a state as possible. On Windows 2000 and above, it is possible for VNC Server to lock the workstation, leaving the current user logged in but requiring that their password be re-entered in order to access their programs or data. Alternatively, VNC Server can completely logoff the current user when there are no more VNC viewers connected, closing any running programs and leaving the workstation ready for another user to log in.

Do nothing

This option tells VNC Server not to perform any action.

Lock workstation

This option causes VNC Server to lock the workstation when the last VNC viewer disconnects.

Note that this option is not available on Windows 95/98/Me and Windows NT 4.

Logoff user

This option causes the current user to be logged off when the last VNC viewer disconnects.

Capture Method

winvnc4 hooks

VNC Server is designed to support a variety of techniques for tracking changes to the local desktop. This release supports basic polling of the screen for changes, as well as the classic VNC Hooks technique.

Poll for changes to the desktop

If this option is selected then VNC Server will poll strips of the screen for changes. The polling mechanism attempts to minimize the load on the server computer while delivering a reasonable level of responsiveness.

Use VNC Hooks to track changes

This option tells VNC Server to use the classic VNC Hooks technique to track graphical updates. This scheme is more efficient than continuous polling but relies on certain properties of Windows applications and so can "miss" updates in some situations. VNC Hooks will also poll the screen infrequently to catch any missed updates.

Poll console windows for updates

The VNC Hooks hooking technique cannot track console windows because of limitations in the operating system. Instead, console windows may be polled for changes. If this option is set then VNC Server will track the visible parts of console windows and poll those areas for changes.

Use VNC Mirror driver to track changes
The VNC Mirror driver is not supported by VNC Open.
Capture alpha-blended windows

This option selects between two screen capture methods. If UseCaptureBlt is false then the faster of the two methods is used, which may in some cases cause alpha-blended windows and tool-tips not to be visible remotely. If UseCaptureBlt is true then these windows will be visible remotely but the VNC Server overhead will be increased.

Note that one aspect of the extra server overhead is that the local cursor will flicker if UserCaptureBlt is enabled.


winvnc4 legacy

Import VNC Open 3.3 Settings

If you have configured WinVNC 3.3 on a machine then you can automatically have VNC Server 4 configure itself to match your existing 3.3 settings as closely as possible. VNC Server 4 will warn you when it cannot match existing settings completely, or if they are no longer relevant.

If you choose to import settings to configure a User-Mode VNC Server then VNC Server will attempt to import your personal WinVNC 3.3 settings. If you choose to import settings to configure a Service-Mode VNC Server then the WinVNC 3.3 Default settings on the local machine will be used.

Note that you must separately uninstall the WinVNC 3.3 service if you import the settings into VNC Server 4, or configure VNC Server 4 to operate on a different port number.

Only use protocol version 3.3

VNC Server 4 supports both the original VNC version 3.3 protocol, and the new VNC protocol version 3.8. Some third-party VNC software use non-standard version numbers which may cause incompatibility issues. VNC Server 4 can therefore be configured only to use the original VNC protocol version, ensuring compatibility even with non-standard VNC Viewers.

Note that this option applies to all VNC connections and reduces the functionality available to connecting VNC Viewers.

Other Options

In addition to the settings described above, the VNC server supports several advanced options. These options can be set on the command-line or by adding an appropriate value to the Windows registry. For User-Mode servers, this value should be added under the HKEY_CURRENT_USER\Software\RealVNC\WinVNC4 key; for Service-Mode servers, the appropriate key is HKEY_LOCAL_MACHINE\Software\RealVNC\WinVNC4.


Disable or enable the Close menu item in the system tray menu. Note that this does not prevent users from shutting down the WinVNC4 process using the Task Manager or the Service Control Manager if they have sufficient access rights to do so.


Disable or enable the Options... menu item in the system tray menu. Note that this does not prevent users from changing the settings in the Windows registry if they have sufficient access rights to do so.


The display device to remote, or empty to remote all displays. The format of display is \\.\<device>. For example, \\.\display1.


Keyboard remapping. mappingis a comma-separated string of character mappings, each of the form char->char or char<>char, where char is a hexadecimal keysym. For example, to exchange the " and @ symbols you would specify the following:


For a full list of options, run winvnc4 -help.

Compatibility Notes

Windows 3.11 / Windows NT 3.51 / Windows 95

VNC Open is not designed to operate on Windows 3.11 or older, Windows NT 3.51 or Windows 95.

Windows 98 / Windows Me

VNC Open is designed to operate on both Windows 98 and Windows Me. Because these platforms are inherently insecure, it is not possible to protect the VNC Server settings from unauthorized access.

Windows XP and Windows 2000 Server

VNC Server is only capable of providing access to session zero. If a different user session is the active console session whena VNC viewer connects, VNC Server will attempt to make session zero the console session.


If you have difficulties which are not covered by this document, try reading the Knowledge Base. There are also some pages to help with troubleshooting.