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 16, other possible values are 8, 15, and 24 - 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 -cc 3 As an alternative to the default TrueColor visual, this allows
58 you to run an Xvnc server with a PseudoColor visual (i.e. one
59 which uses a colour map or palette), which can be useful for
60 running some old X applications which only work on such a dis‐
61 play. Values other than 3 (PseudoColor) and 4 (TrueColor) for
62 the -cc option may result in strange behaviour, and PseudoColor
63 desktops must be 8 bits deep (i.e. -depth 8).
64 -inetd This significantly changes Xvnc's behaviour so that it can be
67 launched from inetd. See the section below on usage with inetd.
68 -help List all the options and parameters
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74 VNC parameters can be set both via the command-line and through the
75 vncconfig(1) program, and with a VNC-enabled XFree86 server via Options
76 entries in the XF86Config file.
77 Parameters can be turned on with -param or off with -param=0. Parame‐
79 ters which take a value can be specified as -param value. Other valid
80 forms are param=value -param=value --param=value. Parameter names are
81 case-insensitive.
82 -desktop desktop-name
85 Each desktop has a name which may be displayed by the viewer. It
86 defaults to "x11".
87 -rfbport port
90 Specifies the TCP port on which Xvnc listens for connections
91 from viewers (the protocol used in VNC is called RFB - "remote
92 framebuffer"). The default is 5900 plus the display number.
93 -rfbwait time, -ClientWaitTimeMillis time
96 Time in milliseconds to wait for a viewer which is blocking
98 Xvnc. This is necessary because Xvnc is single-threaded and
99 sometimes blocks until the viewer has finished sending or
100 receiving a message - note that this does not mean an update
101 will be aborted after this time. Default is 20000 (20 seconds).
102 -httpd directory
105 Run a mini-HTTP server which serves files from the given direc‐
106 tory. Normally the directory will contain the classes for the
107 Java viewer. In addition, files with a .vnc extension will have
108 certain substitutions made so that a single installation of the
109 Java VNC viewer can be served by separate instances of Xvnc.
110 -httpPort port
113 Specifies the port on which the mini-HTTP server runs. Default
114 is 5800 plus the display number.
115 -rfbauth passwd-file, -PasswordFile passwd-file
118 Specifies the file containing the password used to authenticate
119 viewers. The file is accessed each time a connection comes in,
120 so it can be changed on the fly via vncpasswd(1).
121 -deferUpdate time
124 Xvnc uses a "deferred update" mechanism which enhances perfor‐
125 mance in many cases. After any change to the framebuffer, Xvnc
126 waits for this number of milliseconds (default 40) before send‐
127 ing an update to any waiting clients. This means that more
128 changes tend to get coalesced together in a single update. Set‐
129 ting it to 0 results in the same behaviour as earlier versions
130 of Xvnc, where the first change to the framebuffer causes an
131 immediate update to any waiting clients.
132 -SendCutText
135 Send clipboard changes to clients (default is on). Note that
136 you must also run vncconfig(1) to get the clipboard to work.
137 -AcceptCutText
140 Accept clipboard updates from clients (default is on). Note
141 that you must also run vncconfig(1) to get the clipboard to
142 work.
143 -AcceptPointerEvents
146 Accept pointer press and release events from clients (default is
147 on).
148 -AcceptKeyEvents
151 Accept key press and release events from clients (default is
152 on).
153 -DisconnectClients
156 Disconnect existing clients if an incoming connection is non-
157 shared (default is on). If DisconnectClients is false, then a
158 new non-shared connection will be refused while there is a
159 client active. When combined with NeverShared this means only
160 one client is allowed at a time.
161 -NeverShared
164 Never treat incoming connections as shared, regardless of the
165 client-specified setting (default is off).
166 -AlwaysShared
169 Always treat incoming connections as shared, regardless of the
170 client-specified setting (default is off).
171 -Protocol3.3
174 Always use protocol version 3.3 for backwards compatibility with
175 badly-behaved clients (default is off).
176 -CompareFB
179 Perform pixel comparison on framebuffer to reduce unnecessary
180 updates (default is on).
181 -SecurityTypes sec-types
184 Specify which security schemes to use separated by commas. At
185 present only "None" and "VncAuth" are supported. The default is
186 "VncAuth" - note that if you want a server which does not
187 require a password, you must set this parameter to "None".
188 -IdleTimeout seconds
191 The number of seconds after which an idle VNC connection will be
192 dropped (default is 3600 i.e. an hour).
193 -QueryConnect
196 Prompts the user of the desktop to explicitly accept or reject
197 incoming connections. This is most useful when using the vnc.so
198 module or x0vncserver(1) program to access an existing X desktop
199 via VNC.
200 The vncconfig(1) program must be running on the desktop in order
202 for QueryConnect to be supported by the vnc.so(1) module or
203 Xvnc(1) program. The x0vncserver(1) program does not require
204 vncconfig(1) to be running.
205 -localhost
208 Only allow connections from the same machine. Useful if you use
209 SSH and want to stop non-SSH connections from any other hosts.
210 See the guide to using VNC with SSH on the web site.
211 -log logname:dest:level
214 Configures the debug log settings. dest can currently be stderr
215 or stdout, and level is between 0 and 100, 100 meaning most ver‐
216 bose output. logname is usually * meaning all, but you can tar‐
217 get a specific source file if you know the name of its "Log‐
218 Writer". Default is *:stderr:30.
219 -RemapKeys mapping
222 Sets up a keyboard mapping. mapping is a comma-separated string
223 of character mappings, each of the form char->char, or
224 char<>char, where char is a hexadecimal keysym. For example, to
225 exchange the " and @ symbols you would specify the following:
226 RemapKeys=0x22<>0x40
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231 By configuring the inetd(1) service appropriately, Xvnc can be launched
232 on demand when a connection comes in, rather than having to be started
233 manually. When given the -inetd option, instead of listening for TCP
234 connections on a given port it uses its standard input and standard
235 output. There are two modes controlled by the wait/nowait entry in the
236 inetd.conf file.
237 In the nowait mode, Xvnc uses its standard input and output directly as
239 the connection to a viewer. It never has a listening socket, so cannot
240 accept further connections from viewers (it can however connect out to
241 listening viewers by use of the vncconfig program). Further viewer
242 connections to the same TCP port result in inetd spawning off a new
243 Xvnc to deal with each connection. When the connection to the viewer
244 dies, the Xvnc and any associated X clients die. This behaviour is
245 most useful when combined with the XDMCP options -query and -once. An
246 typical example in inetd.conf might be (all on one line):
247 5950 stream tcp nowait nobody /usr/local/bin/Xvnc Xvnc -inetd
249 -query localhost -once securitytypes=none
250 In this example a viewer connection to :50 will result in a new Xvnc
252 for that connection which should display the standard XDM login screen
253 on that machine. Because the user needs to login via XDM, it is usu‐
254 ally OK to accept connections without a VNC password in this case.
255 In the wait mode, when the first connection comes in, inetd gives the
257 listening socket to Xvnc. This means that for a given TCP port, there
258 is only ever one Xvnc at a time. Further viewer connections to the
259 same port are accepted by the same Xvnc in the normal way. Even when
260 the original connection is broken, the Xvnc will continue to run. If
261 this is used with the XDMCP options -query and -once, the Xvnc and
262 associated X clients will die when the user logs out of the X session
263 in the normal way. It is important to use a VNC password in this case.
264 A typical entry in inetd.conf might be:
265 5951 stream tcp wait james /usr/local/bin/Xvnc Xvnc -inetd
267 -query localhost -once passwordFile=/home/james/.vnc/passwd
268 In fact typically, you would have one entry for each user who uses VNC
270 regularly, each of whom has their own dedicated TCP port which they
271 use. In this example, when user "james" connects to :51, he enters his
272 VNC password, then gets the XDM login screen where he logs in in the
273 normal way. However, unlike the previous example, if he disconnects,
274 the session remains persistent, and when he reconnects he will get the
275 same session back again. When he logs out of the X session, the Xvnc
276 will die, but of course a new one will be created automatically the
277 next time he connects.
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281 vncconfig(1), vncpasswd(1), vncserver(1), vncviewer(1), Xserver(1),
282 inetd(1)
283 http://www.realvnc.com
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287 Tristan Richardson, RealVNC Ltd.
288 VNC was originally developed by the RealVNC team while at Olivetti
290 Research Ltd / AT&T Laboratories Cambridge. It is now being maintained
291 by RealVNC Ltd. See http://www.realvnc.com for details.
292RealVNC Ltd 03 Mar 2005 Xvnc(1)