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
43 Specify the pixel depth in bits of the desktop to be created.
44 Default is 24, other possible values are 8, 15, and 16 - any‐
45 thing else is likely to cause strange behaviour by applications.
46 -pixelformat format
48 Specify pixel format for server to use (BGRnnn or RGBnnn). The
49 default for depth 8 is BGR233 (meaning the most significant two
50 bits represent blue, the next three green, and the least signif‐
51 icant three represent red), the default for depth 16 is RGB565
52 and for depth 24 is RGB888.
53 -interface IP address
55 Listen on interface. By default Xvnc listens on all available
56 interfaces.
57 -inetd This significantly changes Xvnc's behaviour so that it can be
59 launched from inetd. See the section below on usage with inetd.
60 -help List all the options and parameters
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65 VNC parameters can be set both via the command-line and through the
66 vncconfig(1) program, and with a VNC-enabled Xorg server via Options
67 entries in the xorg.conf file.
68 Parameters can be turned on with -param or off with -param=0. Parame‐
70 ters which take a value can be specified as -param value. Other valid
71 forms are param=value -param=value --param=value. Parameter names are
72 case-insensitive.
73 -desktop desktop-name
76 Each desktop has a name which may be displayed by the viewer. It
77 defaults to "x11".
78 -rfbport port
80 Specifies the TCP port on which Xvnc listens for connections
81 from viewers (the protocol used in VNC is called RFB - "remote
82 framebuffer"). The default is 5900 plus the display number.
83 -UseIPv4
85 Use IPv4 for incoming and outgoing connections. Default is on.
86 -UseIPv6
88 Use IPv6 for incoming and outgoing connections. Default is on.
89 -rfbunixpath path
91 Specifies the path of a Unix domain socket on which Xvnc listens
92 for connections from viewers, instead of listening on a TCP
93 port.
94 -rfbunixmode mode
96 Specifies the mode of the Unix domain socket. The default is
97 0600.
98 -rfbwait time, -ClientWaitTimeMillis time
100 Time in milliseconds to wait for a viewer which is blocking the
101 server. This is necessary because the server is single-threaded
102 and sometimes blocks until the viewer has finished sending or
103 receiving a message - note that this does not mean an update
104 will be aborted after this time. Default is 20000 (20 seconds).
105 -httpd directory
107 Run a mini-HTTP server which serves files from the given direc‐
108 tory. Normally the directory will contain the classes for the
109 Java viewer. In addition, files with a .vnc extension will have
110 certain substitutions made so that a single installation of the
111 Java VNC viewer can be served by separate instances of Xvnc.
112 -httpPort port
114 Specifies the port on which the mini-HTTP server runs. Default
115 is 5800 plus the display number.
116 -rfbauth passwd-file, -PasswordFile passwd-file
118 Password file for VNC authentication. There is no default, you
119 should specify the password file explicitly. Password file
120 should be created with the vncpasswd(1) utility. The file is
121 accessed each time a connection comes in, so it can be changed
122 on the fly.
123 -AcceptCutText
125 Accept clipboard updates from clients. Default is on.
126 -MaxCutText bytes
128 The maximum size of a clipboard update that will be accepted
129 from a client. Default is 262144.
130 -SendCutText
132 Send clipboard changes to clients. Default is on.
133 -SendPrimary
135 Send the primary selection and cut buffer to the server as well
136 as the clipboard selection. Default is on.
137 -AcceptPointerEvents
139 Accept pointer press and release events from clients. Default is
140 on.
141 -AcceptKeyEvents
143 Accept key press and release events from clients. Default is on.
144 -AcceptSetDesktopSize
146 Accept requests to resize the size of the desktop. Default is
147 on.
148 -DisconnectClients
150 Disconnect existing clients if an incoming connection is non-
151 shared. Default is on. If DisconnectClients is false, then a new
152 non-shared connection will be refused while there is a client
153 active. When combined with NeverShared this means only one
154 client is allowed at a time.
155 -NeverShared
157 Never treat incoming connections as shared, regardless of the
158 client-specified setting. Default is off.
159 -AlwaysShared
161 Always treat incoming connections as shared, regardless of the
162 client-specified setting. Default is off.
163 -Protocol3.3
165 Always use protocol version 3.3 for backwards compatibility with
166 badly-behaved clients. Default is off.
167 -FrameRate fps
169 The maximum number of updates per second sent to each client. If
170 the screen updates any faster then those changes will be aggre‐
171 gated and sent in a single update to the client. Note that this
172 only controls the maximum rate and a client may get a lower rate
173 when resources are limited. Default is 60.
174 -CompareFB mode
176 Perform pixel comparison on framebuffer to reduce unnecessary
177 updates. Can be either 0 (off), 1 (always) or 2 (auto). Default
178 is 2.
179 -ZlibLevel level
181 Zlib compression level for ZRLE encoding (it does not affect
182 Tight encoding). Acceptable values are between 0 and 9.
183 Default is to use the standard compression level provided by the
184 zlib(3) compression library.
185 -ImprovedHextile
187 Use improved compression algorithm for Hextile encoding which
188 achieves better compression ratios by the cost of using slightly
189 more CPU time. Default is on.
190 -SecurityTypes sec-types
192 Specify which security scheme to use for incoming connections.
193 Valid values are a comma separated list of None, VncAuth, Plain,
194 TLSNone, TLSVnc, TLSPlain, X509None, X509Vnc and X509Plain.
195 Default is VncAuth,TLSVnc.
196 -Password password
198 Obfuscated binary encoding of the password which clients must
199 supply to access the server. Using this parameter is insecure,
200 use PasswordFile parameter instead.
201 -PlainUsers user-list
203 A comma separated list of user names that are allowed to authen‐
204 ticate via any of the "Plain" security types (Plain, TLSPlain,
205 etc.). Specify * to allow any user to authenticate using this
206 security type. Default is to deny all users.
207 -pam_service name, -PAMService name
209 PAM service name to use when authentication users using any of
210 the "Plain" security types. Default is vnc.
211 -X509Cert path
213 Path to a X509 certificate in PEM format to be used for all X509
214 based security types (X509None, X509Vnc, etc.).
215 -X509Key path
217 Private key counter part to the certificate given in X509Cert.
218 Must also be in PEM format.
219 -GnuTLSPriority priority
221 GnuTLS priority string that controls the TLS session’s handshake
222 algorithms. See the GnuTLS manual for possible values. Default
223 is NORMAL.
224 -BlacklistThreshold count
226 The number of unauthenticated connection attempts allowed from
227 any individual host before that host is black-listed. Default
228 is 5.
229 -BlacklistTimeout seconds
231 The initial timeout applied when a host is first black-listed.
232 The host cannot re-attempt a connection until the timeout
233 expires. Default is 10.
234 -IdleTimeout seconds
236 The number of seconds after which an idle VNC connection will be
237 dropped. Default is 0, which means that idle connections will
238 never be dropped.
239 -MaxDisconnectionTime seconds
241 Terminate when no client has been connected for N seconds.
242 Default is 0.
243 -MaxConnectionTime seconds
245 Terminate when a client has been connected for N seconds.
246 Default is 0.
247 -MaxIdleTime seconds
249 Terminate after N seconds of user inactivity. Default is 0.
250 -QueryConnect
252 Prompts the user of the desktop to explicitly accept or reject
253 incoming connections. Default is off.
254 The vncconfig(1) program must be running on the desktop in order
256 for QueryConnect to be supported.
257 -QueryConnectTimeout seconds
259 Number of seconds to show the Accept Connection dialog before
260 rejecting the connection. Default is 10.
261 -localhost
263 Only allow connections from the same machine. Useful if you use
264 SSH and want to stop non-SSH connections from any other hosts.
265 -Log logname:dest:level
267 Configures the debug log settings. dest can currently be
268 stderr, stdout or syslog, and level is between 0 and 100, 100
269 meaning most verbose output. logname is usually * meaning all,
270 but you can target a specific source file if you know the name
271 of its "LogWriter". Default is *:stderr:30.
272 -RemapKeys mapping
274 Sets up a keyboard mapping. mapping is a comma-separated string
275 of character mappings, each of the form char->char, or
276 char<>char, where char is a hexadecimal keysym. For example, to
277 exchange the " and @ symbols you would specify the following:
278 RemapKeys=0x22<>0x40
280 -AvoidShiftNumLock
282 Key affected by NumLock often require a fake Shift to be
283 inserted in order for the correct symbol to be generated. Turn‐
284 ing on this option avoids these extra fake Shift events but may
285 result in a slightly different symbol (e.g. a Return instead of
286 a keypad Enter).
287 -RawKeyboard
289 Send keyboard events straight through and avoid mapping them to
290 the current keyboard layout. This effectively makes the keyboard
291 behave according to the layout configured on the server instead
292 of the layout configured on the client. Default is off.
293 -AllowOverride
295 Comma separated list of parameters that can be modified using
296 VNC extension. Parameters can be modified for example using
297 vncconfig(1) program from inside a running session.
298 Allowing override of parameters such as PAMService or Password‐
300 File can negatively impact security if Xvnc runs under different
301 user than the programs allowed to override the parameters.
302 When NoClipboard parameter is set, allowing override of SendCut‐
304 Text and AcceptCutText has no effect.
305 Default is desktop,AcceptPointerEvents,SendCutText,AcceptCut‐
307 Text,SendPrimary,SetPrimary.
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311 By configuring the inetd(1) service appropriately, Xvnc can be launched
312 on demand when a connection comes in, rather than having to be started
313 manually. When given the -inetd option, instead of listening for TCP
314 connections on a given port it uses its standard input and standard
315 output. There are two modes controlled by the wait/nowait entry in the
316 inetd.conf file.
317 In the nowait mode, Xvnc uses its standard input and output directly as
319 the connection to a viewer. It never has a listening socket, so cannot
320 accept further connections from viewers (it can however connect out to
321 listening viewers by use of the vncconfig program). Further viewer
322 connections to the same TCP port result in inetd spawning off a new
323 Xvnc to deal with each connection. When the connection to the viewer
324 dies, the Xvnc and any associated X clients die. This behaviour is
325 most useful when combined with the XDMCP options -query and -once. An
326 typical example in inetd.conf might be (all on one line):
327 5950 stream tcp nowait nobody /usr/local/bin/Xvnc Xvnc -inetd
329 -query localhost -once securitytypes=none
330 In this example a viewer connection to :50 will result in a new Xvnc
332 for that connection which should display the standard XDM login screen
333 on that machine. Because the user needs to login via XDM, it is usu‐
334 ally OK to accept connections without a VNC password in this case.
335 In the wait mode, when the first connection comes in, inetd gives the
337 listening socket to Xvnc. This means that for a given TCP port, there
338 is only ever one Xvnc at a time. Further viewer connections to the
339 same port are accepted by the same Xvnc in the normal way. Even when
340 the original connection is broken, the Xvnc will continue to run. If
341 this is used with the XDMCP options -query and -once, the Xvnc and
342 associated X clients will die when the user logs out of the X session
343 in the normal way. It is important to use a VNC password in this case.
344 A typical entry in inetd.conf might be:
345 5951 stream tcp wait james /usr/local/bin/Xvnc Xvnc -inetd
347 -query localhost -once passwordFile=/home/james/.vnc/passwd
348 In fact typically, you would have one entry for each user who uses VNC
350 regularly, each of whom has their own dedicated TCP port which they
351 use. In this example, when user "james" connects to :51, he enters his
352 VNC password, then gets the XDM login screen where he logs in in the
353 normal way. However, unlike the previous example, if he disconnects,
354 the session remains persistent, and when he reconnects he will get the
355 same session back again. When he logs out of the X session, the Xvnc
356 will die, but of course a new one will be created automatically the
357 next time he connects.
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361 vncconfig(1), vncpasswd(1), vncserver(1), vncviewer(1), Xserver(1),
362 inetd(1)
363 http://www.tigervnc.org
364
367 Tristan Richardson, RealVNC Ltd. and others.
368 VNC was originally developed by the RealVNC team while at Olivetti
370 Research Ltd / AT&T Laboratories Cambridge. TightVNC additions were
371 implemented by Constantin Kaplinsky. Many other people have since par‐
372 ticipated in development, testing and support. This manual is part of
373 the TigerVNC software suite.
374TigerVNC Xvnc(1)