ssvncviewer(1) an X viewer client for VNC


ssvncviewer [options] [host][:display]
ssvncviewer [options] [host][::port]
ssvncviewer [options] exec=[cmd+args...]
ssvncviewer [options] fd=n
ssvncviewer [options] /path/to/unix/socket
ssvncviewer [options] unix=/path/to/unix/socket
ssvncviewer [options] -listen [display]
ssvncviewer -help


ssvncviewer is an Xt-based client application for the VNC (Virtual Network Computing) system. It can connect to any VNC-compatible server such as Xvnc, WinVNC, or x11vnc, allowing you to control desktop environment of a different machine.

ssvncviewer is an enhanced version of the tightvnc unix viewer that can take advantage of features in the x11vnc and UltraVNC VNC servers. See below for the description of these features.

You can use F8 to display a pop-up utility menu (also F7 on MacOSX.) Press F8 twice to pass single F8 to the remote side.


Prints a short usage notice to stderr.
Make the viewer listen on port 5500+display for reverse connections from a server. WinVNC supports reverse connections using the "Add New Client" menu option, or the -connect command line option. Xvnc requires the use of the helper program vncconnect.
-via gateway
Automatically create encrypted TCP tunnel to the gateway machine before connection, connect to the host through that tunnel (TightVNC-specific). By default, this option invokes SSH local port forwarding, assuming that SSH client binary can be accessed as /usr/bin/ssh. Note that when using the -via option, the host machine name should be specified as known to the gateway machine, e.g. "localhost" denotes the gateway, not the machine where vncviewer was launched. See the ENVIRONMENT section below for the information on configuring the -via option.
When connecting, specify that a shared connection is requested. In TightVNC, this is the default mode, allowing you to share the desktop with other clients already using it.
When connecting, specify that the session may not be shared. This would either disconnect other connected clients or refuse your connection, depending on the server configuration.
Disable transfer of mouse and keyboard events from the client to the server.
Start in full-screen mode. Please be aware that operating in full-screen mode may confuse X window managers. Typically, such conflicts cause incorrect handling of input focus or make the viewer window disappear mysteriously. See the grabKeyboard setting in the RESOURCES section below for a method to solve input focus problem.
By default, the viewer shows and raises its window on remote beep (bell) event. This option disables such behaviour (TightVNC-specific).
-user username
User name for Unix login authentication. Default is to use current Unix user name. If this option was given, the viewer will prefer Unix login authentication over the standard VNC authentication.
-passwd passwd-file
File from which to get the password (as generated by the vncpasswd(1) program). This option affects only the standard VNC authentication.
-encodings encoding-list
TightVNC supports several different compression methods to encode screen updates; this option specifies a set of them to use in order of preference. Encodings are specified separated with spaces, and must thus be enclosed in quotes if more than one is specified. Commas may be used to avoid spaces. Available encodings, in default order for a remote connection, are "copyrect tight hextile zlib corre rre raw". For a local connection (to the same machine), the default order to try is "raw copyrect tight hextile zlib corre rre". Raw encoding is always assumed as a last option if no other encoding can be used for some reason. For more information on encodings, see the section ENCODINGS below.
Always use the BGR233 format to encode pixel data. This reduces network traffic, but colors may be represented inaccurately. The bgr233 format is an 8-bit "true color" format, with 2 bits blue, 3 bits green, and 3 bits red.
Try to use a PseudoColor visual and a private colormap. This allows the VNC server to control the colormap.
-truecolour, -truecolor
Try to use a TrueColor visual.
-depth depth
On an X server which supports multiple TrueColor visuals of different depths, attempt to use the specified one (in bits per pixel); if successful, this depth will be requested from the VNC server.
-compresslevel level
Use specified compression level (0..9) for "tight" and "zlib" encodings (TightVNC-specific). Level 1 uses minimum of CPU time and achieves weak compression ratios, while level 9 offers best compression but is slow in terms of CPU time consumption on the server side. Use high levels with very slow network connections, and low levels when working over high-speed LANs. It's not recommended to use compression level 0, reasonable choices start from the level 1.
-quality level
Use the specified JPEG quality level (0..9) for the "tight" encoding (TightVNC-specific). Quality level 0 denotes bad image quality but very impressive compression ratios, while level 9 offers very good image quality at lower compression ratios. Note that the "tight" encoder uses JPEG to encode only those screen areas that look suitable for lossy compression, so quality level 0 does not always mean unacceptable image quality.
Disable lossy JPEG compression in Tight encoding (TightVNC-specific). Disabling JPEG compression is not a good idea in typical cases, as that makes the Tight encoder less efficient. You might want to use this option if it's absolutely necessary to achieve perfect image quality (see also the -quality option).
Disable cursor shape updates, protocol extensions used to handle remote cursor movements locally on the client side (TightVNC-specific). Using cursor shape updates decreases delays with remote cursor movements, and can improve bandwidth usage dramatically.
Use a real X11 cursor with X-style cursor shape updates, instead of drawing the remote cursor on the framebuffer. This option also disables the dot cursor, and disables cursor position updates in non-fullscreen mode.
Read a plain-text password from stdin. This option affects only the standard VNC authentication.

Enhanced TightVNC Viewer (SSVNC) OPTIONS

Enhanced TightVNC Viewer (SSVNC) web page is located at:
Note: ZRLE and ZYWRLE encodings are now supported.
Note: F9 is shortcut to Toggle FullScreen mode.
Note: In -listen mode set the env var. SSVNC_MULTIPLE_LISTEN=1
to allow more than one incoming VNC server at a time. This is the same as -multilisten described below. Set SSVNC_MULTIPLE_LISTEN=MAX:n to allow no more than "n" simultaneous reverse connections.

If the host:port is specified as "exec=command args..." then instead of making a TCP/IP socket connection to the remote VNC server, "command args..." is executed and the viewer is attached to its stdio. This enables tunnelling established via an external command, e.g. an stunnel(8) that does not involve a listening socket. This mode does not work for -listen reverse connections. To not have the exec= pid killed at exit, set SSVNC_NO_KILL_EXEC_CMD=1.

If the host:port is specified as "fd=n" then it is assumed n is an already opened file descriptor to the socket. (i.e the parent did fork+exec)

If the host:port contains a '/' and exists in the file system it is interpreted as a unix-domain socket (AF_LOCAL/AF_UNIX instead of AF_INET) Prefix with unix= to force interpretation as a unix-domain socket.

As in -listen (reverse connection listening) except allow more than one incoming VNC server to be connected at a time. The default for -listen of only one at a time tries to play it safe by not allowing anyone on the network to put (many) desktops on your screen over a long window of time. Use -multilisten for no limit.
In -listen (reverse connection listening) mode when a reverse VNC connection comes in show a popup asking whether to Accept or Reject the connection. The IP address of the connecting host is shown. Same as setting the env. var. SSVNC_ACCEPT_POPUP=1.
As in -acceptpopup except assume UltraVNC Single Click (SC) server. Retrieve User and ComputerName info from UltraVNC Server and display in the Popup.
In -bgr233 mode, use 64 colors instead of 256.
Same as -use64.
In -bgr233 mode, use 8 colors instead of 256.
Same as -use8.
If the vnc viewer X display is depth 24 at 32bpp request a 16bpp format from the VNC server to cut network traffic by up to 2X, then tranlate the pixels to 32bpp locally.
Same as -16bpp.
Use a grey scale for the 16- and 8-bpp modes.
Use alphablending transparency for local cursors requires: x11vnc server, both client and server must be 32bpp and same endianness.
-scale str
Scale the desktop locally. The string "str" can a floating point ratio, e.g. "0.9", or a fraction, e.g. "3/4", or WxH, e.g. 1280x1024. Use "fit" to fit in the current screen size. Use "auto" to fit in the window size. "str" can also be set by the env. var. SSVNC_SCALE.

If you observe mouse trail painting errors, enable X11 Cursor mode (either via Popup or -x11cursor.)

Note that scaling is done in software and so can be slow and requires more memory. Some speedup Tips:

ZRLE is faster than Tight in this mode. When scaling is first detected, the encoding will be automatically switched to ZRLE. Use the Popup menu if you want to go back to Tight. Set SSVNC_PRESERVE_ENCODING=1 to disable this.

Use a solid background on the remote side. (e.g. manually or via x11vnc -solid ...)

If the remote server is x11vnc, try client side caching: x11vnc -ncache 10 ...

-ycrop n
Only show the top n rows of the framebuffer. For use with x11vnc -ncache client caching option to help "hide" the pixel cache region. Use a negative value (e.g. -1) for autodetection. Autodetection will always take place if the remote fb height is more than 2 times the width.
-sbwidth n
Scrollbar width for x11vnc -ncache mode (-ycrop), default is very narrow: 2 pixels, it is narrow to avoid distraction in -ycrop mode.
Disable bell.
Prefer raw encoding for localhost, default is no, i.e. assumes you have a SSH tunnel instead.
Try to avoid using the terminal for interactive responses: use windows for messages and prompting instead. Messages will also be printed to terminal.
Send the X CLIPBOARD selection (i.e. Ctrl+C, Ctrl+V) instead of the X PRIMARY selection (mouse select and middle button paste.)
Whenever the mouse enters the VNC viewer main window, send the selection to the VNC server even if it has not changed. This is like the Xt resource translation SelectionToVNC(always)
str When cut text is received from the VNC server, ssvncviewer will set both the X PRIMARY and the X CLIPBOARD local selections. To control which is set, specify 'str' as 'primary', 'clipboard', or 'both' (the default.)
Grab the entire X server when in fullscreen mode, needed by some old window managers like fvwm2.
Warp the popup back to the pointer position, needed by some old window managers like fvwm2.
Grab the X keyboard when in fullscreen mode, needed by some window managers. Same as -grabkeyboard. -grabkbd is the default, use -nograbkbd to disable.
-bs, -nobs
Whether or not to use X server Backingstore for the main viewer window. The default is to not, mainly because most Linux, etc, systems X servers disable *all* Backingstore by default. To re-enable it put

Option "Backingstore"

in the Device section of /etc/X11/xorg.conf. In -bs mode with no X server backingstore, whenever an area of the screen is re-exposed it must go out to the VNC server to retrieve the pixels. This is too slow.

In -nobs mode, memory is allocated by the viewer to provide its own backing of the main viewer window. This actually makes some activities faster (changes in large regions) but can appear to "flash" too much.

Disable use of MIT shared memory extension (not recommended)
Do the UltraVNC chat in the terminal vncviewer is in instead of in an independent window.
-unixpw str
Useful for logging into x11vnc in -unixpw mode. "str" is a string that allows many ways to enter the Unix Username and Unix Password. These characters: username, newline, password, newline are sent to the VNC server after any VNC authentication has taken place. Under x11vnc they are used for the -unixpw login. Other VNC servers could do something similar.

You can also indicate "str" via the environment variable SSVNC_UNIXPW.

Note that the Escape key is actually sent first to tell x11vnc to not echo the Unix Username back to the VNC viewer. Set SSVNC_UNIXPW_NOESC=1 to override this.

If str is ".", then you are prompted at the command line for the username and password in the normal way. If str is "-" the stdin is read via getpass(3) for username@password. Otherwise if str is a file, it is opened and the first line read is taken as the Unix username and the 2nd as the password. If str prefixed by "rm:" the file is removed after reading. Otherwise, if str has a "@" character, it is taken as username@password. Otherwise, the program exits with an error. Got all that?

-repeater str
This is for use with UltraVNC repeater proxy described here: The "str" is the ID string to be sent to the repeater. E.g. ID:1234 It can also be the hostname and port or display of the VNC server, e.g. or Note that when using -repeater, the host:dpy on the cmdline is the repeater server, NOT the VNC server. The repeater will connect you.

Example: vncviewer ... -repeater ID:3333

Example: vncviewer ... -repeater vhost:0

Use, e.g., '-repeater SCIII=ID:3210' if the repeater is a Single Click III (SSL) repeater (repeater_SSL.exe) and you are passing the SSL part of the connection through stunnel, socat, etc. This way the magic UltraVNC string 'testB' needed to work with the repeater is sent to it.

-rfbversion str
Set the advertised RFB version. E.g.: -rfbversion 3.6 For some servers, e.g. UltraVNC this needs to be done.
UltraVNC has symmetric private encryption DSM plugins. See It is assumed you are using a unix program (e.g. our ultravnc_dsm_helper) to encrypt and decrypt the UltraVNC DSM stream. IN ADDITION TO THAT supply -ultradsm to tell THIS viewer to modify the RFB data sent so as to work with the UltraVNC Server. For some reason, each RFB msg type must be sent twice under DSM.
-mslogon user
Use Windows MS Logon to an UltraVNC server. Supply the username or "1" to be prompted. The default is to autodetect the UltraVNC MS Logon server and prompt for the username and password.

IMPORTANT NOTE: The UltraVNC MS-Logon Diffie-Hellman exchange is very weak and can be brute forced to recover your username and password in a few seconds of CPU time. To be safe, be sure to use an additional encrypted tunnel (e.g. SSL or SSH) for the entire VNC session.

Try to be a client that only does UltraVNC text chat. This mode is used by x11vnc to present a chat window on the physical X11 console (i.e. to chat with the person at the display).
To save writing a shell script to set environment variables, specify as many as you need on the command line. For example, -env SSVNC_MULTIPLE_LISTEN=MAX:5 -env EDITOR=vi
Disable all IPv6 sockets. Same as VNCVIEWER_NO_IPV6=1.
Disable all IPv4 sockets. Same as VNCVIEWER_NO_IPV4=1.
Print out the Ssvnc X resources (appdefaults) and then exit. You can save them to a file and customize them (e.g. the keybindings and Popup menu) Then point to the file via XENVIRONMENT or XAPPLRESDIR.
Like TurboVNC, request the next framebuffer update as soon as possible instead of waiting until the end of the current framebuffer update coming in. Helps 'pipeline' the updates. This is currently the default, use -nopipeline to disable.
Enable features for use with x11vnc's -appshare mode where instead of sharing the full desktop only the application's windows are shared. Viewer multilisten mode is used to create the multiple windows: -multilisten is implied. See 'x11vnc -appshare -help' more information on the mode. Features enabled in the viewer under -appshare are: Minimum extra text in the title, auto -ycrop is disabled, x11vnc -remote_prefix X11VNC_APPSHARE_CMD: message channel, x11vnc initial window position hints. See also Escape Keys below for additional key and mouse bindings.
-escape str
This sets the 'Escape Keys' modifier sequence and enables escape keys mode. When the modifier keys escape sequence is held down, the next keystroke is interpreted locally to perform a special action instead of being sent to the remote VNC server.

Use '-escape default' for the default modifier sequence. (Unix: Alt_L,Super_L and MacOSX: Control_L,Meta_L)

Here are the 'Escape Keys: Help+Set' instructions from the Popup:

Escape Keys: Enter a comma separated list of modifier keys to be the 'escape sequence'. When these keys are held down, the next keystroke is interpreted locally to invoke a special action instead of being sent to the remote VNC server. In other words, a set of 'Hot Keys'.

Here is the list of local key mappings to special actions:

r: refresh desktop b: toggle bell c: toggle full-color

f: file transfer x: x11cursor z: toggle Tight/ZRLE

l: full screen g: graball e: escape keys dialog

s: scale dialog +: scale up (=) -: scale down (_)

t: text chat a: alphablend cursor

V: toggle viewonly Q: quit viewer 123456: UltraVNC scale 1/n

Arrow keys: pan the viewport about 10% for each keypress.

PageUp/PageDown: pan the viewport by a screenful vertically.

Home/End: pan the viewport by a screenful horizontally.

KeyPad Arrows: pan the viewport by 1 pixel for each keypress.

Dragging the Mouse with Button1 pressed also pans the viewport.

Clicking Mouse Button3 brings up the Popup Menu.

The above mappings are always active in ViewOnly mode, unless you set the Escape Keys value to 'never'.

x11vnc -appshare hot-keys: x11vnc has a simple application sharing mode that enables the viewer-side to move, resize, or raise the remote toplevel windows. To enable it, hold down Shift + the Escape Keys and press these:

Arrow keys: move the remote window around in its desktop.

PageUp/PageDn/Home/End: resize the remote window.

+/-: raise or lower the remote window.

M or Button1 move win to local position; D or Button3: delete remote win.

If the Escape Keys value below is set to 'default' then a default list of of modifier keys is used. For Unix it is: Alt_L,Super_L and for MacOSX it is Control_L,Meta_L. Note: the Super_L key usually has a Windows(TM) Flag on it. Also note the _L and _R mean the key is on the LEFT or RIGHT side of the keyboard.

On Unix the default is Alt and Windows keys on Left side of keyboard. On MacOSX the default is Control and Command keys on Left side of keyboard.

Example: Press and hold the Alt and Windows keys on the LEFT side of the keyboard and then press 'c' to toggle the full-color state. Or press 't' to toggle the ultravnc Text Chat window, etc.

To use something besides the default, supply a comma separated list (or a single one) from: Shift_L Shift_R Control_L Control_R Alt_L Alt_R Meta_L Meta_R Super_L Super_R Hyper_L Hyper_R or Mode_switch.

New Popup actions:

 ViewOnly:                ~ -viewonly
 Disable Bell:            ~ -nobell
 Cursor Shape:            ~ -nocursorshape
 X11 Cursor:              ~ -x11cursor
 Cursor Alphablend:       ~ -alpha
 Toggle Tight/Hextile:    ~ -encodings hextile...
 Toggle Tight/ZRLE:       ~ -encodings zrle...
 Toggle ZRLE/ZYWRLE:      ~ -encodings zywrle...
 Quality Level            ~ -quality (both Tight and ZYWRLE)
 Compress Level           ~ -compresslevel
 Disable JPEG:            ~ -nojpeg  (Tight)
 Pipeline Updates         ~ -pipeline

 Full Color                 as many colors as local screen allows.
 Grey scale (16 & 8-bpp)  ~ -grey, for low colors 16/8bpp modes only.
 16 bit color (BGR565)    ~ -16bpp / -bgr565
 8  bit color (BGR233)    ~ -bgr233
 256 colors               ~ -bgr233 default # of colors.
  64 colors               ~ -bgr222 / -use64
   8 colors               ~ -bgr111 / -use8
 Scale Viewer             ~ -scale
 Escape Keys: Toggle      ~ -escape
 Escape Keys: Help+Set    ~ -escape
 Set Y Crop (y-max)       ~ -ycrop
 Set Scrollbar Width      ~ -sbwidth
 XGrabServer              ~ -graball

 UltraVNC Extensions:

   Set 1/n Server Scale     Ultravnc ext. Scale desktop by 1/n.
   Text Chat                Ultravnc ext. Do Text Chat.
   File Transfer            Ultravnc ext. File xfer via Java helper.
   Single Window            Ultravnc ext. Grab and view a single window.
                            (select then click on the window you want).
   Disable Remote Input     Ultravnc ext. Try to prevent input and
                            viewing of monitor at physical display.

 Note: the Ultravnc extensions only apply to servers that support
       them.  x11vnc/libvncserver supports some of them.

 Send Clipboard not Primary  ~ -sendclipboard
 Send Selection Every time   ~ -sendalways


The server supplies information in whatever format is desired by the client, in order to make the client as easy as possible to implement. If the client represents itself as able to use multiple formats, the server will choose one.

Pixel format refers to the representation of an individual pixel. The most common formats are 24 and 16 bit "true-color" values, and 8-bit "color map" representations, where an arbitrary map converts the color number to RGB values.

Encoding refers to how a rectangle of pixels are sent (all pixel information in VNC is sent as rectangles). All rectangles come with a header giving the location and size of the rectangle and an encoding type used by the data which follows. These types are listed below.

The raw encoding simply sends width*height pixel values. All clients are required to support this encoding type. Raw is also the fastest when the server and viewer are on the same machine, as the connection speed is essentially infinite and raw encoding minimizes processing time.
The Copy Rectangle encoding is efficient when something is being moved; the only data sent is the location of a rectangle from which data should be copied to the current location. Copyrect could also be used to efficiently transmit a repeated pattern.
The Rise-and-Run-length-Encoding is basically a 2D version of run-length encoding (RLE). In this encoding, a sequence of identical pixels are compressed to a single value and repeat count. In VNC, this is implemented with a background color, and then specifications of an arbitrary number of subrectangles and color for each. This is an efficient encoding for large blocks of constant color.
This is a minor variation on RRE, using a maximum of 255x255 pixel rectangles. This allows for single-byte values to be used, reducing packet size. This is in general more efficient, because the savings from sending 1-byte values generally outweighs the losses from the (relatively rare) cases where very large regions are painted the same color.
Here, rectangles are split up in to 16x16 tiles, which are sent in a predetermined order. The data within the tiles is sent either raw or as a variant on RRE. Hextile encoding is usually the best choice for using in high-speed network environments (e.g. Ethernet local-area networks).
Zlib is a very simple encoding that uses zlib library to compress raw pixel data. This encoding achieves good compression, but consumes a lot of CPU time. Support for this encoding is provided for compatibility with VNC servers that might not understand Tight encoding which is more efficient than Zlib in nearly all real-life situations.
Like Zlib encoding, Tight encoding uses zlib library to compress the pixel data, but it pre-processes data to maximize compression ratios, and to minimize CPU usage on compression. Also, JPEG compression may be used to encode color-rich screen areas (see the description of -quality and -nojpeg options above). Tight encoding is usually the best choice for low-bandwidth network environments (e.g. slow modem connections).
The SSVNC viewer has ported the RealVNC ( ZRLE encoding to the unix tightvnc viewer.
The SSVNC viewer has ported the Hitachi lossy wavelet based ZRLE encoding from to the unix tightvnc viewer.


X resources that vncviewer knows about, aside from the normal Xt resources, are as follows:
Equivalent of -shared/-noshared options. Default true.
Equivalent of -viewonly option. Default false.
Equivalent of -fullscreen option. Default false.
Grab keyboard in full-screen mode. This can help to solve problems with losing keyboard focus. Default false.
Equivalent of -noraiseonbeep option, when set to false. Default true.
Equivalent of -passwd option.
Equivalent of -user option.
Whether to use a dialog box to get the password (true) or get it from the tty (false). Irrelevant if passwordFile is set. Default false.
Equivalent of -encodings option.
Equivalent of -compresslevel option (TightVNC-specific).
Equivalent of -quality option (TightVNC-specific).
Equivalent of -nojpeg option, when set to false. Default true.
Equivalent of -nocursorshape option, when set to false (TightVNC-specific). Default true.
Equivalent of -bgr233 option. Default false.
When using BGR233, try to allocate this many "exact" colors from the BGR233 color cube. When using a shared colormap, setting this resource lower leaves more colors for other X clients. Irrelevant when using truecolor. Default is 256 (i.e. all of them).
If the number of "exact" BGR233 colors successfully allocated is less than 256 then the rest are filled in using the "nearest" colors available. This resource says whether to only use the "exact" BGR233 colors for this purpose, or whether to use other clients' "shared" colors as well. Default true (i.e. use other clients' colors).
Equivalent of -owncmap option. Default false.
Equivalent of -truecolour option. Default false.
Equivalent of -depth option.
Use MIT shared memory extension if on the same machine as the X server. Default true.
wmDecorationWidth, wmDecorationHeight
The total width and height taken up by window manager decorations. This is used to calculate the maximum size of the VNC viewer window. Default is width 4, height 24.
bumpScrollTime, bumpScrollPixels
When in full screen mode and the VNC desktop is bigger than the X display, scrolling happens whenever the mouse hits the edge of the screen. The maximum speed of scrolling is bumpScrollPixels pixels every bumpScrollTime milliseconds. The actual speed of scrolling will be slower than this, of course, depending on how fast your machine is. Default 20 pixels every 25 milliseconds.
The number of buttons in the popup window. See the README file for more information on how to customize the buttons.
For debugging. Default false.
rawDelay, copyRectDelay
For debugging, see the README file for details. Default 0 (off).


When started with the -via option, vncviewer reads the VNC_VIA_CMD environment variable, expands patterns beginning with the "%" character, and executes result as a command assuming that it would create TCP tunnel that should be used for VNC connection. If not set, this environment variable defaults to "/usr/bin/ssh -f -L %L:%H:%R %G sleep 20".

The following patterns are recognized in the VNC_VIA_CMD (note that all the patterns %G, %H, %L and %R must be present in the command template):

A literal "%";
gateway host name;
remote VNC host name, as known to the gateway;
local TCP port number;
remote TCP port number.


Original VNC was developed in AT&T Laboratories Cambridge. TightVNC additions was implemented by Constantin Kaplinsky. Many other people participated in development, testing and support. Karl J. Runge added all of the SSVNC related features and improvements.

Man page authors:
Marcus Brinkmann <[email protected]>,
Terran Melconian <[email protected]>,
Tim Waugh <[email protected]>,
Constantin Kaplinsky <[email protected]>
Karl J. Runge <[email protected]>