# xvnc(1) - the X VNC server

KasmVNC, ""

```
Xvnc [options] :display#
```

<a name="description"></a>

## Description

**Xvnc**
is the X VNC (Virtual Network Computing) server.  It is based on a standard X
server, but it has a "virtual" screen rather than a physical one.  X
applications display themselves on it as if it were a normal X display, but
they can only be accessed via a VNC viewer - see **vncviewer**(1).

So Xvnc is really two servers in one. To the applications it is an X server,
and to the remote VNC users it is a VNC server. By convention we have arranged
that the VNC server display number will be the same as the X server display
number, which means you can use eg. snoopy:2 to refer to display 2 on machine
"snoopy" in both the X world and the VNC world.

The best way of starting **Xvnc** is via the **vncserver** script.  This
sets up the environment appropriately and runs some X applications to get you
going.  See the manual page for **vncserver**(1) for more information.


<a name="options"></a>

## Options

**Xvnc**
takes lots of options - running **Xvnc -help** gives a list.  Many of these
are standard X server options, which are described in the **Xserver**(1)
manual page.  In addition to options which can only be set via the
command-line, there are also "parameters" which can be set both via the
command-line and through the **vncconfig**(1) program.


* **-geometry _width_x_height_**  
  Specify the size of the desktop to be created. Default is 1024x768.
* **-depth _depth_**  
  Specify the pixel depth in bits of the desktop to be created. Default is 24,
  other possible values are 16 and 32. Anything else is likely to cause strange
  behaviour by applications and may prevent the server from starting at all.
* **-pixelformat _format_**  
  Specify pixel format for server to use (BGRnnn or RGBnnn). The default for
  depth 16 is RGB565 and for depth 24 and 32 is RGB888.
* **-interface _IP address_**  
  Listen on interface. By default Xvnc listens on all available interfaces.
* **-inetd**  
  This significantly changes Xvnc's behaviour so that it can be launched from
  inetd.  See the section below on usage with inetd.
* **-help**  
  List all the options and parameters
  

<a name="parameters"></a>

## Parameters

VNC parameters can be set both via the command-line and through the
**vncconfig**(1) program, and with a VNC-enabled Xorg server via Options
entries in the xorg.conf file.

Parameters can be turned on with -_param_ or off with
-_param_=0.  Parameters which take a value can be specified as
-_param_ _value_.  Other valid forms are _param_**=**_value_
-_param_=_value_ --_param_=_value_.  Parameter names are
case-insensitive.


* **-desktop _desktop-name_**  
  Each desktop has a name which may be displayed by the viewer. It defaults to
  "x11".
* **-rfbport _port_**  
  Specifies the TCP port on which Xvnc listens for connections from viewers (the
  protocol used in VNC is called RFB - "remote framebuffer").  The default is
  5900 plus the display number.
* **-UseIPv4**  
  Use IPv4 for incoming and outgoing connections. Default is on.
* **-UseIPv6**  
  Use IPv6 for incoming and outgoing connections. Default is on.
* **-rfbunixpath _path_**  
  Specifies the path of a Unix domain socket on which Xvnc listens for
  connections from viewers, instead of listening on a TCP port.
* **-rfbunixmode _mode_**  
  Specifies the mode of the Unix domain socket.  The default is 0600.
* **-rfbwait _time_, -ClientWaitTimeMillis _time_**  
  Time in milliseconds to wait for a viewer which is blocking the server. This is
  necessary because the server is single-threaded and sometimes blocks until the
  viewer has finished sending or receiving a message - note that this does not
  mean an update will be aborted after this time.  Default is 20000 (20 seconds).
* **-httpd _directory_**  
  Run a mini-HTTP server which serves files from the given directory.  Normally
  the directory will contain the kasmweb client. It will use the websocket port.
* **-http-header _header=val_**  
  Append this header to all HTTP responses (file and API). May be given multiple
  times.
* **-rfbauth _passwd-file_, -PasswordFile _passwd-file_**  
  Password file for VNC authentication.  There is no default, you should
  specify the password file explicitly.  Password file should be created with
  the **vncpasswd**(1) utility.  The file is accessed each time a connection
  comes in, so it can be changed on the fly.
* **-KasmPasswordFile _passwd-file_**  
  Password file for BasicAuth, created with the **kasmvncpasswd** utility.
  Default _~/.kasmpasswd_.
* **-PublicIP _my-ip_**  
  The server's public IP, for UDP negotiation. If not set, will be queried via the internet.
  Default unset.
* **-StunServer _srv_**  
  Use this STUN server for querying the server's public IP. If not set, a hardcoded list of
  STUN servers is used.
  Default unset.
* **-udpFullFrameFrequency _frames_**  
  Send a full frame every N frames for clients using UDP. 0 to disable. Default _0_.
* **-udpPort _port_**  
  Which port to use for UDP. Default same as websocket.
* **-AcceptCutText**  
  Accept clipboard updates from clients. Default is on.
* **-SendCutText**  
  Send clipboard changes to clients. Default is on.
* **-SendPrimary**  
  Send the primary selection and cut buffer to the server as well as the
  clipboard selection. Default is off.
* **-AcceptPointerEvents**  
  Accept pointer press and release events from clients. Default is on.
* **-AcceptKeyEvents**  
  Accept key press and release events from clients. Default is on.
* **-AcceptSetDesktopSize**  
  Accept requests to resize the size of the desktop. Default is on.
* **-DisconnectClients**  
  Disconnect existing clients if an incoming connection is non-shared. Default is
  on. If **DisconnectClients** is false, then a new non-shared connection will
  be refused while there is a client active.  When combined with
  **NeverShared** this means only one client is allowed at a time.
* **-NeverShared**  
  Never treat incoming connections as shared, regardless of the client-specified
  setting. Default is off.
* **-AlwaysShared**  
  Always treat incoming connections as shared, regardless of the client-specified
  setting. Default is off.
* **-Protocol3.3**  
  Always use protocol version 3.3 for backwards compatibility with badly-behaved
  clients. Default is off.
* **-FrameRate _fps_**  
  The maximum number of updates per second sent to each client. If the screen
  updates any faster then those changes will be aggregated and sent in a single
  update to the client. Note that this only controls the maximum rate and a
  client may get a lower rate when resources are limited. Default is **60**.
* **-DynamicQualityMin _min_**  
  The minimum quality to with dynamic JPEG quality scaling. The accepted values
  are 0-9 where 0 is low and 9 is high, with the same meaning as the client-side
  -quality parameter. Default is **7**.
* **-DynamicQualityMax _max_**  
  The maximum quality to use with dynamic JPEG quality scaling. Setting this to
  zero disables dynamic JPEG quality scaling. The accepted values are 0-9 where 0
  is low and 9 is high, with the same meaning as the client-side -quality parameter.
  Default is **8**.
* **-TreatLossless _quality_**  
  Treat lossy quality levels above and including this as lossless, without
  sending lossless updates for them. 0-9, 10 disables this.
  Default is **10**.
* **-PreferBandwidth**  
  Prefer bandwidth over quality, and set various options for lower bandwidth use.
  The default is off, aka to prefer quality. You can override individual values
  by setting them after this switch on the command line. This switch sets the
  following:  
  - dynamic JPEG quality range 2-9  
  - TreatLossless 8
* **-RectThreads _num_**  
  Use this many threads to compress rects in parallel. Default **0** (automatic),
  set to **1** to disable.
* **-JpegVideoQuality _num_**  
  The JPEG quality to use when in video mode.
  Default **-1**.
* **-WebpVideoQuality _num_**  
  The WEBP quality to use when in video mode.
  Default **-1**.
  **-MaxVideoResolution _1920x1080_**
  When in video mode, downscale the screen to max this size. Keeps aspect ratio.
  Default **1920x1080**.
* **-VideoTime _seconds_**  
  High rate of change must happen for this many seconds to switch to video mode.
  Default **5**, set **0** to always enable.
* **-VideoOutTime _seconds_**  
  The rate of change must be below the VideoArea threshold for this many seconds
  to switch out of video mode.
  Default **3**.
* **-VideoArea _percentage_**  
  High rate of change must happen for this % of the screen to switch to video mode.
  Default **45**.
* **-PrintVideoArea**  
  Print the detected video area % value.
  Default off.
* **-VideoScaling _type_**  
  Scaling method to use when in downscaled video mode. 0 = nearest, 1 = bilinear,
  2 = progressive bilinear.
  Default **2**.
* **-CompareFB _mode_**  
  Perform pixel comparison on framebuffer to reduce unnecessary updates. Can
  be either **0** (off), **1** (always) or **2** (auto). Default is
  **2**.
* **-hw3d**  
  Enable hardware 3d acceleration. Default is software (llvmpipe usually).
* **-drinode _path_**  
  Use another path instead of /dev/dri/renderD128. You may need this if you have
  more than one GPU.
* **-ZlibLevel _level_**  
  Zlib compression level for ZRLE encoding (it does not affect Tight encoding).
  Acceptable values are between 0 and 9.  Default is to use the standard
  compression level provided by the **zlib**(3) compression library.
* **-ImprovedHextile**  
  Use improved compression algorithm for Hextile encoding which achieves better
  compression ratios by the cost of using slightly more CPU time.  Default is
  on.
* **-IgnoreClientSettingsKasm**  
  Ignore the additional client settings exposed in Kasm. Default off.
  Kasm exposes a few settings to the client the standard VNC does not.
  This param lets the server ignore those.
* **-DLP_Region _x1,y1,x2,y2_**  
  Black out anything outside this region. x1,y1 is the upper-left corner,
  and x2,y2 the lower-left. In addition to absolute pixel values, percentages
  are allowed, zero means "default", and a negative number means "border".
* **-DLP_RegionAllowClick _bool_**  
  Allow clicks inside the blacked-out region.
* **-DLP_RegionAllowRelease _bool_**  
  Allow click releases inside the blacked-out region.
* **-DLP_ClipSendMax _bytes_**  
  Limit clipboard bytes to send to clients in one transaction. Default 0.
  0 disables the limit, use **SendCutText** to disable clipboard sending entirely.
* **-DLP_ClipAcceptMax _bytes_**  
  Limit clipboard bytes to receive from clients in one transaction. Default 0.
  0 disables the limit, use **AcceptCutText** to disable clipboard receiving entirely.
* **-DLP_ClipDelay _ms_**  
  This many milliseconds must pass between clipboard actions. Default 0, 0 disables the limit.
* **-DLP_ClipTypes _a,b_**  
  Allowed binary clipboard mimetypes, separated by commas. Default
  chromium/x-web-custom-data,text/html,image/png
* **-DLP_KeyRateLimit _keys-per-second_**  
  Reject keyboard presses over this many per second. Default 0 (disabled).
* **-DLP_Log _off/info/verbose_**  
  Log clipboard and keyboard actions. Info logs just clipboard direction and size,
  verbose adds the contents for both.
* **-DLP_WatermarkImage _path/to/file.png_**  
  Add a watermark. The PNG file should be greyscale, black is treated as transparent
  and white as opaque.
* **-DLP_WatermarkLocation _x,y_**  
  Place the watermark at this position from the corner. Positive numbers are from top-left,
  negative from bottom-right. Negative numbers count from the bottom-right edge of the image.
  If not set, the watermark will be centered. Cannot be used together with repeat.
* **-DLP_WatermarkRepeatSpace _num_**  
  If set, repeat the watermark over the entire image, with **num** pixels between
  repetitions. Cannot be used together with location.
* **-DLP_WatermarkTint _r,g,b,a_**  
  Tint the greyscale watermark by this color. Default is 255,255,255,255 - full white.
  The color components can be used to colorize the greyscale watermark, and the alpha
  can be used to make it fainter.
* **-selfBench**  
  Run a set of self-benchmarks and exit.
* **-noWebsocket**  
  Disable websockets and expose a traditional VNC port (5901, etc.).
* **-websocketPort _port_**  
  Listen for websocket connections on this port, default 6800.
* **-cert _path_**  
  SSL pem cert to use for websocket connections, default empty/not used.
* **-key _path_**  
  SSL pem key to use for websocket connections, default empty/not used.
  Only use this if you have the cert and key in separate files. If they
  are in the same file, use **-cert**.
* **-sslOnly**  
  Require SSL for websocket connections. Default off, non-SSL allowed.
* **-disableBasicAuth**  
  Disable basic auth for websocket connections. Default enabled, details read from
  the **-KasmPasswordFile**.
* **-SecurityTypes _sec-types_**  
  Specify which security scheme to use for incoming connections.  Valid values
  are a comma separated list of **None**, **VncAuth**, **Plain**,
  **TLSNone**, **TLSVnc**, **TLSPlain**, **X509None**, **X509Vnc**
  and **X509Plain**. Default is **VncAuth,TLSVnc**.
* **-Password _password_**  
  Obfuscated binary encoding of the password which clients must supply to
  access the server.  Using this parameter is insecure, use **PasswordFile**
  parameter instead.
* **-PlainUsers _user-list_**  
  A comma separated list of user names that are allowed to authenticate via
  any of the "Plain" security types (Plain, TLSPlain, etc.). Specify <b>\*</b>
  to allow any user to authenticate using this security type. Default is to
  deny all users.
* **-pam_service _name_, -PAMService _name_**  
  PAM service name to use when authentication users using any of the "Plain"
  security types. Default is **vnc**.
* **-X509Cert _path_**  
  Path to a X509 certificate in PEM format to be used for all X509 based
  security types (X509None, X509Vnc, etc.).
* **-X509Key _path_**  
  Private key counter part to the certificate given in **X509Cert**. Must
  also be in PEM format.
* **-GnuTLSPriority _priority_**  
  GnuTLS priority string that controls the TLS session’s handshake algorithms.
  See the GnuTLS manual for possible values. Default is **NORMAL**.
* **-BlacklistThreshold _count_**  
  The number of unauthenticated connection attempts allowed from any individual
  host before that host is black-listed.  Default is 5.
* **-BlacklistTimeout _seconds_**  
  The initial timeout applied when a host is first black-listed.  The host
  cannot re-attempt a connection until the timeout expires.  Default is 10.
* **-IdleTimeout _seconds_**  
  The number of seconds after which an idle VNC connection will be dropped.
  Default is 0, which means that idle connections will never be dropped.
* **-MaxDisconnectionTime _seconds_**  
  Terminate when no client has been connected for _N_ seconds.  Default is
  0.
* **-MaxConnectionTime _seconds_**  
  Terminate when a client has been connected for _N_ seconds.  Default is
  0.
* **-MaxIdleTime _seconds_**  
  Terminate after _N_ seconds of user inactivity.  Default is 0.
* **-QueryConnect**  
  Prompts the user of the desktop to explicitly accept or reject incoming
  connections. Default is off.
  
  The **vncconfig**(1) program must be running on the desktop in order for
  QueryConnect to be supported.
* **-QueryConnectTimeout _seconds_**  
  Number of seconds to show the Accept Connection dialog before rejecting the
  connection.  Default is **10**.
* **-localhost**  
  Only allow connections from the same machine. Useful if you use SSH and want to
  stop non-SSH connections from any other hosts.
* **-Log _logname_:_dest_:_level_**  
  Configures the debug log settings.  _dest_ can currently be **stderr**,
  **stdout** or **syslog**, and _level_ is between 0 and 100, 100 meaning
  most verbose output.  _logname_ is usually <b>\*</b> meaning all, but you can
  target a specific source file if you know the name of its "LogWriter".  Default
  is ***:stderr:30**.
* **-RemapKeys mapping**  
  Sets up a keyboard mapping.
  _mapping_
  is a comma-separated string of character mappings, each of the form
  _char_-&gt;_char_,
  or
  _char_&lt;&gt;_char_,
  where
  _char_
  is a hexadecimal keysym. For example, to exchange the " and @ symbols you would specify the following:
  
      RemapKeys=0x22&lt;&gt;0x40
* **-AvoidShiftNumLock**  
  Key affected by NumLock often require a fake Shift to be inserted in order
  for the correct symbol to be generated. Turning on this option avoids these
  extra fake Shift events but may result in a slightly different symbol
  (e.g. a Return instead of a keypad Enter).
* **-RawKeyboard**  
  Send keyboard events straight through and avoid mapping them to the current
  keyboard layout. This effectively makes the keyboard behave according to the
  layout configured on the server instead of the layout configured on the
  client. Default is off.
* **-AllowOverride**  
  Comma separated list of parameters that can be modified using VNC extension.
  Parameters can be modified for example using **vncconfig**(1) program from
  inside a running session.
  
  Allowing override of parameters such as **PAMService** or **PasswordFile**
  can negatively impact security if Xvnc runs under different user than the
  programs allowed to override the parameters.
  
  When **NoClipboard** parameter is set, allowing override of **SendCutText**
  and **AcceptCutText** has no effect.
  
  Default is **desktop,AcceptPointerEvents,SendCutText,AcceptCutText,SendPrimary,SetPrimary**.
  

<a name="usage-with-inetd"></a>

## Usage with Inetd

By configuring the **inetd**(1) service appropriately, Xvnc can be launched
on demand when a connection comes in, rather than having to be started
manually.  When given the **-inetd** option, instead of listening for TCP
connections on a given port it uses its standard input and standard output.
There are two modes controlled by the wait/nowait entry in the inetd.conf file.

In the nowait mode, Xvnc uses its standard input and output directly as the
connection to a viewer.  It never has a listening socket, so cannot accept
further connections from viewers (it can however connect out to listening
viewers by use of the vncconfig program).  Further viewer connections to the
same TCP port result in inetd spawning off a new Xvnc to deal with each
connection.  When the connection to the viewer dies, the Xvnc and any
associated X clients die.  This behaviour is most useful when combined with the
XDMCP options -query and -once.  An typical example in inetd.conf might be (all
on one line):

5950   stream   tcp nowait nobody  /usr/local/bin/Xvnc Xvnc -inetd -query
localhost -once securitytypes=none

In this example a viewer connection to :50 will result in a new Xvnc for that
connection which should display the standard XDM login screen on that machine.
Because the user needs to login via XDM, it is usually OK to accept connections
without a VNC password in this case.

In the wait mode, when the first connection comes in, inetd gives the listening
socket to Xvnc.  This means that for a given TCP port, there is only ever one
Xvnc at a time.  Further viewer connections to the same port are accepted by
the same Xvnc in the normal way.  Even when the original connection is broken,
the Xvnc will continue to run.  If this is used with the XDMCP options -query
and -once, the Xvnc and associated X clients will die when the user logs out of
the X session in the normal way.  It is important to use a VNC password in this
case.  A typical entry in inetd.conf might be:

5951   stream   tcp wait   james     /usr/local/bin/Xvnc Xvnc -inetd -query localhost -once passwordFile=/home/james/.vnc/passwd

In fact typically, you would have one entry for each user who uses VNC
regularly, each of whom has their own dedicated TCP port which they use.  In
this example, when user "james" connects to :51, he enters his VNC password,
then gets the XDM login screen where he logs in in the normal way.  However,
unlike the previous example, if he disconnects, the session remains persistent,
and when he reconnects he will get the same session back again.  When he logs
out of the X session, the Xvnc will die, but of course a new one will be
created automatically the next time he connects.


<a name="see-also"></a>

## See Also

**vncconfig**(1),
**vncpasswd**(1),
**vncserver**(1),
**vncviewer**(1),
**Xserver**(1),
**inetd**(1)  
http://kasmweb.com


<a name="author"></a>

## Author

Kasm Technologies Corp., Tristan Richardson, RealVNC Ltd., D. R. Commander and others.

VNC was originally developed by the RealVNC team while at Olivetti
Research Ltd / AT&T Laboratories Cambridge.  TightVNC additions were
implemented by Constantin Kaplinsky. Many other people have since
participated in development, testing and support. KasmVNC has since
forked and the project and has added many modern features and made
the solution web native.

This manual is part of the KasmVNC software suite.