1Xvnc(1) Virtual Network Computing Xvnc(1)
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6 Xvnc - the X VNC server
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9 Xvnc [options] :display#
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12 Xvnc is the X VNC (Virtual Network Computing) server. It is based on a
13 standard X server, but it has a "virtual" screen rather than a physical
14 one. X applications display themselves on it as if it were a normal X
15 display, but they can only be accessed via a VNC viewer - see
16 vncviewer(1).
17 So Xvnc is really two servers in one. To the applications it is an X
19 server, and to the remote VNC users it is a VNC server. By convention
20 we have arranged that the VNC server display number will be the same as
21 the X server display number, which means you can use eg. snoopy:2 to
22 refer to display 2 on machine "snoopy" in both the X world and the VNC
23 world.
24 The best way of starting Xvnc is via the vncserver script. This sets
26 up the environment appropriately and runs some X applications to get
27 you going. See the manual page for vncserver(1) for more information.
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31 Xvnc takes lots of options - running Xvnc -help gives a list. Many of
32 these are standard X server options, which are described in the
33 Xserver(1) manual page. In addition to options which can only be set
34 via the command-line, there are also "parameters" which can be set both
35 via the command-line and through the vncconfig(1) program.
36 -geometry widthxheight
39 Specify the size of the desktop to be created. Default is
40 1024x768.
41 -depth depth
44 Specify the pixel depth in bits of the desktop to be created.
45 Default is 24, other possible values are 8, 15, and 16 - any‐
46 thing else is likely to cause strange behaviour by applications.
47 -pixelformat format
50 Specify pixel format for server to use (BGRnnn or RGBnnn). The
51 default for depth 8 is BGR233 (meaning the most significant two
52 bits represent blue, the next three green, and the least signif‐
53 icant three represent red), the default for depth 16 is RGB565
54 and for depth 24 is RGB888.
55 -interface IP address or -i IP address
58 Listen on interface. By default Xvnc listens on all available
59 interfaces.
60 -cc 3 As an alternative to the default TrueColor visual, this allows
63 you to run an Xvnc server with a PseudoColor visual (i.e. one
64 which uses a color map or palette), which can be useful for run‐
65 ning some old X applications which only work on such a display.
66 Values other than 3 (PseudoColor) and 4 (TrueColor) for the -cc
67 option may result in strange behaviour, and PseudoColor desktops
68 must be 8 bits deep (i.e. -depth 8).
69 -inetd This significantly changes Xvnc's behaviour so that it can be
72 launched from inetd. See the section below on usage with inetd.
73 -help List all the options and parameters
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79 VNC parameters can be set both via the command-line and through the
80 vncconfig(1) program, and with a VNC-enabled Xorg server via Options
81 entries in the xorg.conf file.
82 Parameters can be turned on with -param or off with -param=0. Parame‐
84 ters which take a value can be specified as -param value. Other valid
85 forms are param=value -param=value --param=value. Parameter names are
86 case-insensitive.
87 -desktop desktop-name
90 Each desktop has a name which may be displayed by the viewer. It
91 defaults to "x11".
92 -rfbport port
95 Specifies the TCP port on which Xvnc listens for connections
96 from viewers (the protocol used in VNC is called RFB - "remote
97 framebuffer"). The default is 5900 plus the display number.
98 -rfbwait time, -ClientWaitTimeMillis time
101 Time in milliseconds to wait for a viewer which is blocking
103 Xvnc. This is necessary because Xvnc is single-threaded and
104 sometimes blocks until the viewer has finished sending or
105 receiving a message - note that this does not mean an update
106 will be aborted after this time. Default is 20000 (20 seconds).
107 -httpd directory
110 Run a mini-HTTP server which serves files from the given direc‐
111 tory. Normally the directory will contain the classes for the
112 Java viewer. In addition, files with a .vnc extension will have
113 certain substitutions made so that a single installation of the
114 Java VNC viewer can be served by separate instances of Xvnc.
115 -httpPort port
118 Specifies the port on which the mini-HTTP server runs. Default
119 is 5800 plus the display number.
120 -rfbauth passwd-file, -PasswordFile passwd-file
123 Specifies the file containing the password used to authenticate
124 viewers. The file is accessed each time a connection comes in,
125 so it can be changed on the fly via vncpasswd(1).
126 -deferUpdate time
129 Xvnc uses a "deferred update" mechanism which enhances perfor‐
130 mance in many cases. After any change to the framebuffer, Xvnc
131 waits for this number of milliseconds (default 1) before sending
132 an update to any waiting clients. This means that more changes
133 tend to get coalesced together in a single update. Setting it to
134 0 results in the same behaviour as earlier versions of Xvnc,
135 where the first change to the framebuffer causes an immediate
136 update to any waiting clients.
137 -SendCutText
140 Send clipboard changes to clients (default is on). Note that
141 you must also run vncconfig(1) to get the clipboard to work.
142 -AcceptCutText
145 Accept clipboard updates from clients (default is on). Note
146 that you must also run vncconfig(1) to get the clipboard to
147 work.
148 -AcceptPointerEvents
151 Accept pointer press and release events from clients (default is
152 on).
153 -AcceptKeyEvents
156 Accept key press and release events from clients (default is
157 on).
158 -DisconnectClients
161 Disconnect existing clients if an incoming connection is non-
162 shared (default is on). If DisconnectClients is false, then a
163 new non-shared connection will be refused while there is a
164 client active. When combined with NeverShared this means only
165 one client is allowed at a time.
166 -NeverShared
169 Never treat incoming connections as shared, regardless of the
170 client-specified setting (default is off).
171 -AlwaysShared
174 Always treat incoming connections as shared, regardless of the
175 client-specified setting (default is off).
176 -Protocol3.3
179 Always use protocol version 3.3 for backwards compatibility with
180 badly-behaved clients (default is off).
181 -CompareFB
184 Perform pixel comparison on framebuffer to reduce unnecessary
185 updates (default is on).
186 -SecurityTypes sec-types
189 Specify which security schemes to use separated by commas. At
190 present only "None" and "VncAuth" are supported. The default is
191 "VncAuth" - note that if you want a server which does not
192 require a password, you must set this parameter to "None".
193 -IdleTimeout seconds
196 The number of seconds after which an idle VNC connection will be
197 dropped (default is 0, which means that idle connections will
198 never be dropped).
199 -QueryConnect
202 Prompts the user of the desktop to explicitly accept or reject
203 incoming connections. This is most useful when using the vnc.so
204 module or x0vncserver(1) program to access an existing X desktop
205 via VNC.
206 The vncconfig(1) program must be running on the desktop in order
208 for QueryConnect to be supported by the vnc.so(1) module or
209 Xvnc(1) program. The x0vncserver(1) program does not require
210 vncconfig(1) to be running.
211 -localhost
214 Only allow connections from the same machine. Useful if you use
215 SSH and want to stop non-SSH connections from any other hosts.
216 See the guide to using VNC with SSH on the web site.
217 -log logname:dest:level
220 Configures the debug log settings. dest can currently be stderr
221 or stdout, and level is between 0 and 100, 100 meaning most ver‐
222 bose output. logname is usually * meaning all, but you can tar‐
223 get a specific source file if you know the name of its "Log‐
224 Writer". Default is *:stderr:30.
225 -RemapKeys mapping
228 Sets up a keyboard mapping. mapping is a comma-separated string
229 of character mappings, each of the form char->char, or
230 char<>char, where char is a hexadecimal keysym. For example, to
231 exchange the " and @ symbols you would specify the following:
232 RemapKeys=0x22<>0x40
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237 By configuring the inetd(1) service appropriately, Xvnc can be launched
238 on demand when a connection comes in, rather than having to be started
239 manually. When given the -inetd option, instead of listening for TCP
240 connections on a given port it uses its standard input and standard
241 output. There are two modes controlled by the wait/nowait entry in the
242 inetd.conf file.
243 In the nowait mode, Xvnc uses its standard input and output directly as
245 the connection to a viewer. It never has a listening socket, so cannot
246 accept further connections from viewers (it can however connect out to
247 listening viewers by use of the vncconfig program). Further viewer
248 connections to the same TCP port result in inetd spawning off a new
249 Xvnc to deal with each connection. When the connection to the viewer
250 dies, the Xvnc and any associated X clients die. This behaviour is
251 most useful when combined with the XDMCP options -query and -once. An
252 typical example in inetd.conf might be (all on one line):
253 5950 stream tcp nowait nobody /usr/local/bin/Xvnc Xvnc -inetd
255 -query localhost -once securitytypes=none
256 In this example a viewer connection to :50 will result in a new Xvnc
258 for that connection which should display the standard XDM login screen
259 on that machine. Because the user needs to login via XDM, it is usu‐
260 ally OK to accept connections without a VNC password in this case.
261 In the wait mode, when the first connection comes in, inetd gives the
263 listening socket to Xvnc. This means that for a given TCP port, there
264 is only ever one Xvnc at a time. Further viewer connections to the
265 same port are accepted by the same Xvnc in the normal way. Even when
266 the original connection is broken, the Xvnc will continue to run. If
267 this is used with the XDMCP options -query and -once, the Xvnc and
268 associated X clients will die when the user logs out of the X session
269 in the normal way. It is important to use a VNC password in this case.
270 A typical entry in inetd.conf might be:
271 5951 stream tcp wait james /usr/local/bin/Xvnc Xvnc -inetd
273 -query localhost -once passwordFile=/home/james/.vnc/passwd
274 In fact typically, you would have one entry for each user who uses VNC
276 regularly, each of whom has their own dedicated TCP port which they
277 use. In this example, when user "james" connects to :51, he enters his
278 VNC password, then gets the XDM login screen where he logs in in the
279 normal way. However, unlike the previous example, if he disconnects,
280 the session remains persistent, and when he reconnects he will get the
281 same session back again. When he logs out of the X session, the Xvnc
282 will die, but of course a new one will be created automatically the
283 next time he connects.
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287 vncconfig(1), vncpasswd(1), vncserver(1), vncviewer(1), Xserver(1),
288 inetd(1)
289 http://www.tigervnc.org
290
293 Tristan Richardson, RealVNC Ltd.
294 VNC was originally developed by the RealVNC team while at Olivetti
296 Research Ltd / AT&T Laboratories Cambridge. TightVNC additions were
297 implemented by Constantin Kaplinsky. Many other people participated in
298 development, testing and support.
299TigerVNC 17 Apr 2006 Xvnc(1)