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<title>User’s Guide for TurboVNC 3.2</title>
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<link rel="chapter" href="index.html#hd002" title="2 Conventions Used in This Document">
<link rel="chapter" href="index.html#hd003" title="3 Overview">
<link rel="chapter" href="index.html#hd004" title="4 System Requirements">
<link rel="chapter" href="index.html#hd005" title="5 Obtaining and Installing TurboVNC">
<link rel="chapter" href="index.html#hd006" title="6 Using TurboVNC">
<link rel="chapter" href="index.html#hd007" title="7 Performance and Image Quality">
<link rel="chapter" href="index.html#hd008" title="8 TurboVNC Security Extensions">
<link rel="chapter" href="index.html#hd009" title="9 GPU-Accelerated OpenGL (Using VirtualGL with TurboVNC)">
<link rel="chapter" href="index.html#hd0010" title="10 GPU-Accelerated OpenGL and Vulkan (Using the DRI3 X11 Extension)">
<link rel="chapter" href="index.html#hd0011" title="11 Compatibility Guide">
<link rel="chapter" href="index.html#hd0012" title="12 Advanced Configuration">
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<div class="title">
<p class="title">User’s Guide for TurboVNC 3.2</p>
</div>
<div id="hd">
<div id="hdBlock" class="hd">
<ul class="hd">
<li class="Itemize-1 hd">
<a href="#hd001" class="hd">1 Legal Information</a>
</li>
<li class="Itemize-1 hd">
<a href="#hd002" class="hd">2 Conventions Used in This Document</a>
<ul class="hd">
<li class="Itemize-3 hd">
<a href="#hd002001" class="hd">2.1 Terminology</a>
</li>
</ul>
</li>
<li class="Itemize-1 hd">
<a href="#hd003" class="hd">3 Overview</a>
</li>
<li class="Itemize-1 hd">
<a href="#hd004" class="hd">4 System Requirements</a>
<ul class="hd">
<li class="Itemize-3 hd">
<a href="#hd004001" class="hd">4.1 Linux and Other Un*x Operating
Systems</a>
</li>
<li class="Itemize-3 hd">
<a href="#hd004002" class="hd">4.2 Mac</a>
</li>
<li class="Itemize-3 hd">
<a href="#hd004003" class="hd">4.3 Windows</a>
</li>
</ul>
</li>
<li class="Itemize-1 hd">
<a href="#hd005" class="hd">5 Obtaining and Installing TurboVNC</a>
<ul class="hd">
<li class="Itemize-3 hd">
<a href="#hd005001" class="hd">5.1 Installing TurboVNC on Linux</a>
</li>
<li class="Itemize-3 hd">
<a href="#hd005002" class="hd">5.2 Installing the TurboVNC Viewer on
macOS</a>
</li>
<li class="Itemize-3 hd">
<a href="#hd005003" class="hd">5.3 Installing the TurboVNC Viewer on
Windows</a>
</li>
<li class="Itemize-3 hd">
<a href="#hd005004" class="hd">5.4 Installing TurboVNC from Source</a>
</li>
<li class="Itemize-3 hd">
<a href="#hd005005" class="hd">5.5 Uninstalling TurboVNC</a>
</li>
</ul>
</li>
<li class="Itemize-1 hd">
<a href="#hd006" class="hd">6 Using TurboVNC</a>
<ul class="hd">
<li class="Itemize-3 hd">
<a href="#hd006001" class="hd">6.1 The TurboVNC Session Manager</a>
</li>
<li class="Itemize-3 hd">
<a href="#hd006002" class="hd">6.2 Manually Starting a TurboVNC
Session</a>
</li>
<li class="Itemize-3 hd">
<a href="#hd006003" class="hd">6.3 Choosing a Window Manager</a>
</li>
<li class="Itemize-3 hd">
<a href="#hd006004" class="hd">6.4 Manually Connecting to a VNC
Server</a>
</li>
<li class="Itemize-3 hd">
<a href="#hd006005" class="hd">6.5 Disconnecting and Killing a TurboVNC
Session</a>
</li>
<li class="Itemize-3 hd">
<a href="#hd006006" class="hd">6.6 Using TurboVNC in a Web Browser</a>
</li>
<li class="Itemize-3 hd">
<a href="#hd006007" class="hd">6.7 Using SSH to Manually Secure a
TurboVNC Connection</a>
</li>
<li class="Itemize-3 hd">
<a href="#hd006008" class="hd">6.8 Requiring SSH Tunneling</a>
</li>
<li class="Itemize-3 hd">
<a href="#hd006009" class="hd">6.9 Running OpenGL Applications</a>
</li>
<li class="Itemize-3 hd">
<a href="#hd0060010" class="hd">6.10 Further Reading</a>
</li>
</ul>
</li>
<li class="Itemize-1 hd">
<a href="#hd007" class="hd">7 Performance and Image Quality</a>
<ul class="hd">
<li class="Itemize-3 hd">
<a href="#hd007001" class="hd">7.1 Interframe Comparison</a>
</li>
<li class="Itemize-3 hd">
<a href="#hd007002" class="hd">7.2 Advanced Compression Options</a>
</li>
<li class="Itemize-3 hd">
<a href="#hd007003" class="hd">7.3 Lossless Refresh</a>
</li>
<li class="Itemize-3 hd">
<a href="#hd007004" class="hd">7.4 Automatic Lossless Refresh</a>
</li>
<li class="Itemize-3 hd">
<a href="#hd007005" class="hd">7.5 Multithreading</a>
</li>
</ul>
</li>
<li class="Itemize-1 hd">
<a href="#hd008" class="hd">8 TurboVNC Security Extensions</a>
<ul class="hd">
<li class="Itemize-3 hd">
<a href="#hd008001" class="hd">8.1 Terminology</a>
</li>
<li class="Itemize-3 hd">
<a href="#hd008002" class="hd">8.2 TurboVNC Server Authentication
Methods</a>
</li>
<li class="Itemize-3 hd">
<a href="#hd008003" class="hd">8.3 TurboVNC Viewer Authentication
Schemes</a>
</li>
<li class="Itemize-3 hd">
<a href="#hd008004" class="hd">8.4 Supported Encryption Methods</a>
</li>
<li class="Itemize-3 hd">
<a href="#hd008005" class="hd">8.5 Supported Security Types</a>
</li>
<li class="Itemize-3 hd">
<a href="#hd008006" class="hd">8.6 Enabling Security Types</a>
</li>
<li class="Itemize-3 hd">
<a href="#hd008007" class="hd">8.7 Further Reading</a>
</li>
</ul>
</li>
<li class="Itemize-1 hd">
<a href="#hd009" class="hd">9 GPU-Accelerated OpenGL (Using VirtualGL
with TurboVNC)</a>
<ul class="hd">
<li class="Itemize-3 hd">
<a href="#hd009001" class="hd">9.1 Using VirtualGL on a TurboVNC Host</a>
<ul class="hd">
<li class="Itemize-5 hd">
<a href="#hd009001002" class="hd">9.1.2 Running the Window Manager Using
VirtualGL</a>
</li>
</ul>
</li>
<li class="Itemize-3 hd">
<a href="#hd009002" class="hd">9.2 Using VirtualGL on a Machine Other
Than a TurboVNC Host</a>
</li>
<li class="Itemize-3 hd">
<a href="#hd009003" class="hd">9.3 NV-CONTROL Emulation</a>
</li>
</ul>
</li>
<li class="Itemize-1 hd">
<a href="#hd0010" class="hd">10 GPU-Accelerated OpenGL and Vulkan (Using
the DRI3 X11 Extension)</a>
</li>
<li class="Itemize-1 hd">
<a href="#hd0011" class="hd">11 Compatibility Guide</a>
<ul class="hd">
<li class="Itemize-3 hd">
<a href="#hd0011001" class="hd">11.1 TightVNC or TigerVNC Servers</a>
</li>
<li class="Itemize-3 hd">
<a href="#hd0011002" class="hd">11.2 TightVNC or TigerVNC Viewers</a>
</li>
<li class="Itemize-3 hd">
<a href="#hd0011003" class="hd">11.3 RealVNC</a>
</li>
</ul>
</li>
<li class="Itemize-1 hd">
<a href="#hd0012" class="hd">12 Advanced Configuration</a>
<ul class="hd">
<li class="Itemize-3 hd">
<a href="#hd0012001" class="hd">12.1 Server Settings</a>
</li>
<li class="Itemize-3 hd">
<a href="#hd0012002" class="hd">12.2 Viewer Settings</a>
</li>
</ul>
</li>
</ul>
</div></div>
<a name="file000"></a>
<p><br /></p>
<hr class="break" />
<h1 id="hd001"><a name="file001"></a>1 Legal Information</h1>
<p><img src="somerights20.png" alt="somerights20" class="inline" id="imgid_0" name="imgid_0"/></p>
<p>This document and all associated illustrations are licensed under the
<span class="remote"><a href="https://creativecommons.org/licenses/by/2.5" target="_blank" class="remote">Creative
Commons Attribution 2.5 License</a></span><a name="idx001"></a>. Any
works that contain material derived from this document must cite The
VirtualGL Project as the source of the material and list the current URL
for the TurboVNC web site.</p>
<p>The official TurboVNC binaries contain libjpeg-turbo, which is based in
part on the work of the Independent JPEG Group.</p>
<p>TurboVNC is licensed under the <a href="LICENSE.txt" target="_blank">GNU
General Public License, v2</a><a name="idx002"></a>.</p>
<p><br /></p>
<hr class="break" />
<h1 id="hd002"><a name="file002"></a>2 Conventions Used in This Document</h1>
<p>This document assumes that TurboVNC will be installed in the default
directory (<strong class="filename">/opt/TurboVNC</strong> on Linux/Un*x
and Mac systems and <strong class="filename">c:\Program
Files\TurboVNC</strong> on Windows systems.) If your installation of
TurboVNC resides in a different directory, then adjust the instructions
accordingly.</p>
<h2 id="hd002001">2.1 Terminology</h2>
<dl class="Description">
<dt class="Description-1 Description">VNC server (sometimes just “server”)</dt>
<dd class="Description-1 Description">
A computer program, implementing the Remote Framebuffer (RFB) protocol
and usually designed to run as a background process, that provides an
interactive remote desktop environment through which authenticated users
can run graphical programs remotely from other computers on the network.
VNC servers can be implemented as single-user screen scrapers, which
transmit the contents of the host’s physical display (most common
with Windows and Mac VNC servers), or as virtual display servers, which
provide isolated remote desktop environments for an arbitrary number of
simultaneous users on the same host (most common with Un*x VNC servers.)
</dd>
<dt class="Description-1 Description">VNC host (sometimes just “host”)</dt>
<dd class="Description-1 Description">
The machine on which a VNC server is running
</dd>
<dt class="Description-1 Description">VNC viewer (sometimes just “viewer”)</dt>
<dd class="Description-1 Description">
A computer program, implementing the Remote Framebuffer (RFB) protocol,
that connects to a VNC server running on another computer, thus allowing
users to run graphical programs remotely.
</dd>
<dt class="Description-1 Description">client machine (sometimes just “client”)</dt>
<dd class="Description-1 Description">
The machine on which a VNC viewer is running
</dd>
<dt class="Description-1 Description">VNC session (sometimes just “session”)</dt>
<dd class="Description-1 Description">
A specific instance of a Un*x VNC server (Xvnc.) Each instance of an
Xvnc server, including the TurboVNC Server, acts as an independent
virtual X server, listening on a unique X11 display number for
connections from X11 clients and listening on a unique TCP port number
or Unix domain socket for connections from VNC viewers. Multiple
simultaneous VNC sessions can exist on a given host, under any number of
different user accounts.
</dd>
</dl>
<p><br /></p>
<hr class="break" />
<h1 id="hd003"><a name="file003"></a>3 Overview</h1>
<p>TurboVNC is a derivative of VNC (Virtual Network Computing) that is
tuned to provide peak performance for 3D and video workloads. TurboVNC
was originally a fork of
<span class="remote"><a href="https://tightvnc.com" target="_blank" class="remote">TightVNC</a></span><a name="idx003"></a>
1.3.x. However, the current version of TurboVNC contains a modern X
server code base (based on X.org) and a variety of other
<span class="remote"><a href="https://turbovnc.org/About/Features" target="_blank" class="remote">notable
features</a></span><a name="idx004"></a> and fixes relative to TightVNC
1.3.x, including a high-performance cross-platform VNC viewer with
session management capabilities, as well as some unique features
designed specifically for visualization applications. Some of those
features are not available in any other open source Linux/Un*x remote
display solutions. TurboVNC compresses 3D and video workloads
significantly better than the “tightest” compression mode in
TightVNC 1.3.x while using only typically 15-20% of the CPU time of the
latter. Using non-default settings, TurboVNC can also match the best
compression ratios produced by TightVNC 1.3.x for 2D workloads. (See
Section <a href="#AdvancedCompression" class="ref">7.2</a>.)</p>
<p>All VNC implementations, including TurboVNC, use the RFB (remote
framebuffer) protocol to send “framebuffer updates” from the
VNC server to any connected viewers. Each framebuffer update can
contain multiple “rectangles” (regions that have changed
since the last update.) As with TightVNC, TurboVNC analyzes each
rectangle, splits it into multiple “subrectangles”, and
attempts to encode each subrectangle using the “subencoding
type” that will provide the most efficient compression, given the
number of unique colors in the subrectangle. The process by which
TurboVNC does this is referred to as an “encoding method.” A
rectangle is first analyzed to determine if any significant portion of
it is solid, and if so, that portion is encoded as a bounding box and a
fill color (“Solid subencoding.”) Of the remaining
subrectangles, those with only two colors are encoded as a
1-bit-per-pixel bitmap with a 2-color palette (“Mono
subencoding”), those with low numbers of unique colors are encoded
as a color palette and an 8-bit-per-pixel bitmap (“Indexed color
subencoding”), and subrectangles with high numbers of unique
colors are encoded using either JPEG or arrays of RGB pixels (“Raw
subencoding”), depending on the encoding method. zlib can
optionally be used to compress the indexed color, mono and raw
subrectangles.</p>
<p>Part of TurboVNC’s speedup comes from the use of
<span class="remote"><a href="https://libjpeg-turbo.org" target="_blank" class="remote">libjpeg-turbo</a></span><a name="idx005"></a>,
a SIMD-accelerated JPEG codec. However, TurboVNC also eliminates the
CPU-hungry smoothness detection routines that TightVNC uses to determine
whether a subrectangle is a good candidate for JPEG compression, and
TurboVNC’s encoding methods tend to favor the use of JPEG more,
since it is now generally the fastest subencoding type. Furthermore,
TurboVNC eliminates buffer copies, it maximizes network efficiency by
splitting framebuffer updates into relatively large subrectangles, and
it uses only the zlib compression levels that can be shown to have a
measurable performance benefit.</p>
<p>TurboVNC is the product of
<span class="remote"><a href="https://TurboVNC.org/pmwiki/uploads/About/tighttoturbo.pdf" target="_blank" class="remote">extensive
research</a></span><a name="idx006"></a>, in which many different
permutations of the TightVNC encoder were benchmarked at the low level
against a variety of RFB session captures that simulate real-world
application workloads, both 2D and 3D. TurboVNC’s encoding
methods have been adopted by
<span class="remote"><a href="https://tigervnc.org" target="_blank" class="remote">TigerVNC</a></span><a name="idx007"></a>,
<span class="remote"><a href="https://libvnc.github.io" target="_blank" class="remote">LibVNC</a></span><a name="idx008"></a>,
<span class="remote"><a href="https://uvnc.com/" target="_blank" class="remote">UltraVNC</a></span><a name="idx009"></a>,
and other projects.</p>
<p>TurboVNC, when used with
<span class="remote"><a href="https://VirtualGL.org" target="_blank" class="remote">VirtualGL</a></span><a name="idx0010"></a>,
provides a highly performant and robust solution for remotely displaying
3D applications over all types of networks.</p>
<p>On “modern” hardware, TurboVNC is capable of streaming 50+
Megapixels/second over a 100 Megabit/second local area network with
perceptually lossless image quality. TurboVNC can stream between 10 and
12 Megapixels/second over a 5 Megabit/second broadband connection at
reduced (but usable) image quality.</p>
<p>TurboVNC is compatible with other VNC distributions. See Chapter
<a href="#Compatibility" class="ref">11</a> for more information. The
official TurboVNC binaries can be installed onto the same system as
other VNC distributions without interference.</p>
<p><br /></p>
<hr class="break" />
<h1 id="hd004"><a name="file004"></a>4 System Requirements</h1>
<h2 id="hd004001">4.1 Linux and Other Un*x Operating Systems</h2>
<div class="table">
<table class="standard">
<thead class="standard">
<tr class="head ">
<th class="head standard"></th>
<th class="head standard">Host</th>
<th class="head standard">Client (Linux)</th>
<th class="head standard">Client (non-Linux)</th>
</tr>
</thead>
<tr class="standard">
<td class="high standard">CPU</td>
<td class="standard"><ul class="Itemize"><li class="Itemize-0">
x86-64 or AArch64 required
</li>
<li class="Itemize-0">
At least two processors or cores recommended
</li></ul></td>
<td class="standard" colspan="2">x86-64 or AArch64 required</td>
</tr>
<tr class="standard">
<td class="high standard">O/S</td>
<td class="standard" colspan="4">TurboVNC should work with a variety of Linux distributions and <span class="remote"><a href="https://freebsd.org" target="_blank" class="remote">FreeBSD</a></span><a name="idx0011"></a>, but currently-supported versions of <span class="remote"><a href="https://redhat.com/products/enterprise-linux" target="_blank" class="remote">Red Hat Enterprise Linux</a></span><a name="idx0012"></a> and its derivatives, <span class="remote"><a href="https://ubuntu.com" target="_blank" class="remote">Ubuntu</a></span><a name="idx0013"></a> LTS, and <span class="remote"><a href="https://suse.com" target="_blank" class="remote">SUSE</a></span><a name="idx0014"></a> Linux Enterprise tend to receive the most attention from the TurboVNC community.</td>
</tr>
<tr class="standard">
<td class="high standard">Other</td>
<td class="standard">SSH server (if using the <a href="#TurboVNC_Session_Manager">TurboVNC Session Manager</a><a name="idx0015"></a>)</td>
<td class="standard">For optimal performance, the X server should be configured to export True Color (24-bit or 32-bit) visuals.</td>
<td class="standard"><ul class="Itemize"><li class="Itemize-0">
For optimal performance, the X server should be configured to export
True Color (24-bit or 32-bit) visuals.
</li>
<li class="Itemize-0">
<span class="remote"><a href="https://www.java.com" target="_blank" class="remote">Oracle
Java</a></span><a name="idx0016"></a> or OpenJDK
</li></ul></td>
</tr>
</table>
</div>
<h2 id="hd004002">4.2 Mac</h2>
<div class="table">
<table class="standard">
<thead class="standard">
<tr class="head ">
<th class="head standard"></th>
<th class="head standard">Client</th>
</tr>
</thead>
<tr class="standard">
<td class="high standard">CPU</td>
<td class="standard">64-bit Intel or Apple silicon required</td>
</tr>
<tr class="standard">
<td class="high standard">O/S</td>
<td class="standard">macOS 10.12 “Sierra” or later (Intel); macOS 11 “Big Sur” or later (Apple silicon)</td>
</tr>
</table>
</div>
<h2 id="hd004003">4.3 Windows</h2>
<div class="table">
<table class="standard">
<thead class="standard">
<tr class="head ">
<th class="head standard"></th>
<th class="head standard">Client</th>
</tr>
</thead>
<tr class="standard">
<td class="high standard">CPU</td>
<td class="standard">x86-64 required</td>
</tr>
<tr class="standard">
<td class="high standard">O/S</td>
<td class="standard">Windows 7 or later</td>
</tr>
<tr class="standard">
<td class="high standard">Other</td>
<td class="standard">For optimal performance, the client display should have a 24-bit or 32-bit (True Color) color depth.</td>
</tr>
</table>
</div>
<p><br /></p>
<hr class="break" />
<h1 id="hd005"><a name="file005"></a>5 Obtaining and Installing TurboVNC</h1>
<h2 id="hd005001">5.1 Installing TurboVNC on Linux</h2>
<h3 id="hd005001001">Installing TurboVNC</h3>
<ol class="Ordered numeric">
<li class="Ordered-1 Ordered">
Download the appropriate TurboVNC binary package for your system from
the
<span class="remote"><a href="https://github.com/TurboVNC/turbovnc/releases" target="_blank" class="remote">Releases
area</a></span><a name="idx0017"></a> of the
<span class="remote"><a href="https://github.com/TurboVNC/turbovnc" target="_blank" class="remote">TurboVNC
GitHub project page</a></span><a name="idx0018"></a>. RPM and Debian
packages are provided for Linux distributions that contain GLIBC 2.17 or
later. <br />
</li>
<li class="Ordered-1 Ordered">
<code>cd</code> to the directory where you downloaded the binary
package, and issue one of the following commands as root:
<dl class="Description">
<dt class="Description-3 Description">RPM-based systems using YUM</dt>
<dd class="Description-3 Description">
<pre class="verbatim">
yum install turbovnc*.rpm
</pre>
</dd>
<dt class="Description-3 Description">RPM-based systems using DNF</dt>
<dd class="Description-3 Description">
<pre class="verbatim">
dnf install turbovnc*.rpm
</pre>
</dd>
<dt class="Description-3 Description">RPM-based systems using YaST2</dt>
<dd class="Description-3 Description">
<pre class="verbatim">
yast2 --install turbovnc*.rpm
</pre>
</dd>
<dt class="Description-3 Description">Other RPM-based systems (dependencies will not be installed automatically)</dt>
<dd class="Description-3 Description">
<pre class="verbatim">
rpm -U turbovnc*.rpm
</pre>
</dd>
<dt class="Description-3 Description">Debian-based systems</dt>
<dd class="Description-3 Description">
<pre class="verbatim">
dpkg -i turbovnc*.deb
apt install -f
</pre>
</dd>
</dl>
</li>
</ol>
<h3 id="hd005001002">Installing TurboVNC for a Single User</h3>
<p>Download the appropriate binary package, as above, then execute the
following commands:</p>
<dl class="Description">
<dt class="Description-1 Description">RPM-based systems</dt>
<dd class="Description-1 Description">
<pre class="verbatim">mkdir ~/turbovnc<br />cd ~/turbovnc<br />rpm2cpio <em>full/path/of/turbovnc*.rpm</em> | cpio -idv</pre>
</dd>
<dt class="Description-1 Description">Debian-based systems</dt>
<dd class="Description-1 Description">
<pre class="verbatim">dpkg-deb –extract <em>full/path/of/turbovnc*.deb</em> ~/turbovnc</pre>
</dd>
</dl>
<p>Add <strong class="filename">~/turbovnc</strong> to any paths specified
in this document.</p>
<div class="important"><p class="important">
If using the TurboVNC Session Manager, set the TurboVNC Viewer’s <code>ServerDir</code> parameter to <code>"~/turbovnc/opt/TurboVNC"</code>. (<code>~</code> must be quoted or escaped if the parameter is specified on the command line.)
</p></div>
<div class="important"><p class="important">
The TurboVNC security configuration file will not work when TurboVNC is installed in this manner.
</p></div>
<h2 id="hd005002">5.2 Installing the TurboVNC Viewer on macOS</h2>
<ol class="Ordered numeric">
<li class="Ordered-1 Ordered">
Download the TurboVNC Mac disk image
(<strong class="filename">TurboVNC-3.1.91-x86_64.dmg</strong> for Intel
CPUs or <strong class="filename">TurboVNC-3.1.91-arm64.dmg</strong> for
Apple silicon CPUs) from the
<span class="remote"><a href="https://github.com/TurboVNC/turbovnc/releases" target="_blank" class="remote">Releases
area</a></span><a name="idx0019"></a> of the
<span class="remote"><a href="https://github.com/TurboVNC/turbovnc" target="_blank" class="remote">TurboVNC
GitHub project page</a></span><a name="idx0020"></a>.
</li>
<li class="Ordered-1 Ordered">
Open the disk image, then open
<strong class="filename">TurboVNC.pkg</strong> inside the disk image.
Follow the instructions to install the Mac TurboVNC Viewer.
</li>
</ol>
<h2 id="hd005003">5.3 Installing the TurboVNC Viewer on Windows</h2>
<ol class="Ordered numeric">
<li class="Ordered-1 Ordered">
Download the TurboVNC Windows installer package
(<strong class="filename">TurboVNC-3.1.91.exe</strong>) from the
<span class="remote"><a href="https://github.com/TurboVNC/turbovnc/releases" target="_blank" class="remote">Releases
area</a></span><a name="idx0021"></a> of the
<span class="remote"><a href="https://github.com/TurboVNC/turbovnc" target="_blank" class="remote">TurboVNC
GitHub project page</a></span><a name="idx0022"></a>.
</li>
<li class="Ordered-1 Ordered">
Run the TurboVNC installer. The installation of TurboVNC should be
self-explanatory. The only configuration option is the directory into
which you want the files to be installed.
</li>
</ol>
<h2 id="hd005004">5.4 Installing TurboVNC from Source</h2>
<p>If you are using a Linux/Un*x platform for which there is not a
pre-built TurboVNC binary package available, then download the TurboVNC
source tarball
(<strong class="filename">turbovnc-3.1.91.tar.gz</strong>) from the
<span class="remote"><a href="https://github.com/TurboVNC/turbovnc/releases" target="_blank" class="remote">Releases
area</a></span><a name="idx0023"></a> of the
<span class="remote"><a href="https://github.com/TurboVNC/turbovnc" target="_blank" class="remote">TurboVNC
GitHub project page</a></span><a name="idx0024"></a>, uncompress it,
<code>cd turbovnc-3.1.91</code>, and read
<strong class="filename">BUILDING.md</strong> for further instructions
on how to build TurboVNC from source.</p>
<h2 id="hd005005">5.5 Uninstalling TurboVNC</h2>
<h3 id="hd005005001">Linux</h3>
<p>As root, issue one of the following commands:</p>
<dl class="Description">
<dt class="Description-1 Description">RPM-based systems</dt>
<dd class="Description-1 Description">
<pre class="verbatim">
rpm -e turbovnc
</pre>
</dd>
<dt class="Description-1 Description">Debian-based systems</dt>
<dd class="Description-1 Description">
<pre class="verbatim">
dpkg -r turbovnc
</pre>
</dd>
</dl>
<h3 id="hd005005002">macOS</h3>
<p>Open the <strong class="filename">Uninstall TurboVNC</strong>
application, located in the <strong class="filename">TurboVNC</strong>
Applications folder. You can also open a terminal and execute:</p>
<pre class="verbatim">
sudo /opt/TurboVNC/bin/uninstall
</pre>
<h3 id="hd005005003">Windows</h3>
<p>Use the <strong class="filename">Programs and Features</strong> applet
in the Control Panel (or the <strong class="filename">Apps &
Features</strong> applet if you are running Windows 10), or select
<strong class="filename">Uninstall TurboVNC</strong> in the
<strong class="filename">TurboVNC</strong> Start Menu group.</p>
<p><br /></p>
<hr class="break" />
<h1 id="hd006"><a name="file006"></a>6 Using TurboVNC</h1>
<p><a name="TurboVNC_Usage"></a></p>
<h2 id="hd006001">6.1 The TurboVNC Session Manager</h2>
<p><a name="TurboVNC_Session_Manager"></a></p>
<p>The TurboVNC Viewer, like any VNC viewer, can be used to connect to any
VNC server. However, the TurboVNC Viewer also includes the TurboVNC
Session Manager, which can be used with the TurboVNC Server to remotely
start or kill a TurboVNC session, list all TurboVNC sessions running
under a particular user account on a particular host, and choose a
TurboVNC session to which to connect. The TurboVNC Session Manager uses
the TurboVNC Viewer’s built-in SSH client, which supports OpenSSH
config files and password-less public key authentication (using
ssh-agent or Pageant.)</p>
<h3 id="hd006001001">Procedure</h3>
<ul class="Itemize">
<li class="Itemize-1 Itemize asterisk">
On the client machine, start the TurboVNC Viewer.
<dl class="Description">
<dt class="Description-3 Description">Linux/Un*x clients</dt>
<dd class="Description-3 Description">
Open a new terminal/xterm and type
<pre class="verbatim">
/opt/TurboVNC/bin/vncviewer
</pre>
</dd>
<dt class="Description-3 Description">Mac clients</dt>
<dd class="Description-3 Description">
Open the <strong class="filename">TurboVNC Viewer</strong> application,
located in the <strong class="filename">TurboVNC</strong> Applications
folder, or open a new terminal and type
<pre class="verbatim">
/opt/TurboVNC/bin/vncviewer
</pre>
</dd>
<dt class="Description-3 Description">Windows clients</dt>
<dd class="Description-3 Description">
Select <strong class="filename">TurboVNC Viewer</strong> in the
<strong class="filename">TurboVNC</strong> Start Menu group, or open a
new command prompt and type
<pre class="verbatim">
c:\Program Files\TurboVNC\vncviewer.bat
</pre>
</dd>
</dl>
</li>
<li class="Itemize-1 Itemize asterisk">
A small dialog box will appear. <br /><br />
<img src="newconn-sessmgr.png" alt="newconn-sessmgr" class="inline" id="imgid_1" name="imgid_1"/>
<br /><br /> Enter the hostname or IP address of the TurboVNC host in
the “VNC server” field, then click “Connect”.
<br /><br />
</li>
<li class="Itemize-1 Itemize asterisk">
The TurboVNC Session Manager will connect to the host using SSH, and it
will prompt for an SSH private key passphrase or an SSH password, if
necessary. (The TurboVNC Viewer’s built-in SSH client will first
try to fetch the private key passphrase from ssh-agent or Pageant, if
either is running.)
<div class="important"><p class="important">
You can specify the SSH username, if it differs from your local username, by prefixing the hostname/IP address with <code><em>user</em>@</code>, where <em><code>user</code></em> is the SSH username.
</p></div>
</li>
<li class="Itemize-1 Itemize asterisk">
If no TurboVNC sessions are currently running under your user account on
the TurboVNC host, then the session manager will: <br /><br />
<ul class="Itemize">
<li class="Itemize-3 Itemize asterisk">
start a new session
</li>
<li class="Itemize-3 Itemize asterisk">
generate a new one-time password (OTP) for the session
</li>
<li class="Itemize-3 Itemize asterisk">
automatically configure the TurboVNC Viewer so that it tunnels the VNC
connection through SSH (reusing the SSH channel that the session manager
already opened) and authenticates using the newly-generated OTP
</li>
<li class="Itemize-3 Itemize asterisk">
connect to the session
</li>
</ul>
<br class="itempara" />Once connected, a TurboVNC desktop window should appear on your client
machine. This window contains a virtual desktop with which you can
interact to launch X-Windows applications on the TurboVNC host.
<br /><br />
</li>
<li class="Itemize-1 Itemize asterisk">
If one or more TurboVNC sessions are currently running under your user
account on the TurboVNC host, then the session manager will enumerate
the sessions and display a dialog similar to the following, allowing you
to manage the sessions remotely, to start a new session, or to choose a
session to which to connect: <br /><br />
<img src="sessmgr.png" alt="sessmgr" class="inline" id="imgid_2" name="imgid_2"/>
<br /><br /> Upon choosing a session to which to connect, the session
manager will (as described above) automatically generate a new OTP for
the session and configure the TurboVNC Viewer so that it tunnels the VNC
connection through SSH and authenticates using the newly-generated OTP.
<br /><br /> One-time passwords can be used with any VNC viewer, so
generating a new OTP for a TurboVNC session (using the “New
OTP” button) is a convenient way of allowing colleagues to
temporarily access the session. Generating a new OTP for a TurboVNC
session is also useful when using
<a href="#noVNC">noVNC</a><a name="idx0025"></a>. If
“View-only” is checked, then users who authenticate using
the new OTP will not be able to remotely control the session.
<div class="important"><p class="important">
The TurboVNC Session Manager automatically uses SSH tunneling and OTP authentication by default, but you can set the TurboVNC Viewer’s <code>NoSessMgrAuto</code> parameter to disable this behavior, thus allowing any authentication/encryption method to be used. Additional parameters can be used to specify the port on which the SSH server is listening and the location of the SSH private key file. The OpenSSH config file (<strong class="filename">~/.ssh/config</strong> by default) can also be used to specify those parameters persistently for a given host.
</p></div>
<div class="important"><p class="important">
The TurboVNC Viewer’s <code>ServerDir</code> and <code>ServerArgs</code> parameters can be used to specify a non-default installation path for the TurboVNC Server or additional arguments to pass to the TurboVNC Server when starting new sessions. TurboVNC Server arguments can also be specified on the host using the system-wide or per-user <strong class="filename">turbovncserver.conf</strong> file.
</p></div>
</li>
</ul>
<h2 id="hd006002">6.2 Manually Starting a TurboVNC Session</h2>
<h3 id="hd006002001">Procedure</h3>
<ol class="Ordered numeric">
<li class="Ordered-1 Ordered">
Open a new Command Prompt/terminal window on your client machine.
</li>
<li class="Ordered-1 Ordered">
In the new Command Prompt/terminal window, open a Secure Shell (SSH)
session into the TurboVNC host:
<pre class="verbatim">ssh <em>user</em>@<em>host</em></pre>
Replace <em><code>user</code></em> with your username on the TurboVNC
host and <em><code>host</code></em> with the hostname or IP address of
the host.
</li>
<li class="Ordered-1 Ordered">
In the SSH session, start a TurboVNC session:
<pre class="verbatim">
/opt/TurboVNC/bin/vncserver
</pre>
</li>
<li class="Ordered-1 Ordered">
Make a note of the X display number that the TurboVNC session is
occupying, for instance: <br /><br />
<code>Desktop 'TurboVNC: my_host:1 (my_user)' started on display my_host:1</code>
<br /><br /> If this is the first time that a TurboVNC session has ever
been run under this user account, and if VNC password authentication is
enabled for the session, then TurboVNC will prompt for a VNC password.
</li>
<li class="Ordered-1 Ordered">
The SSH session can now be exited, if desired.
</li>
</ol>
<h2 id="hd006003">6.3 Choosing a Window Manager</h2>
<p>By default, a window manager is launched in a TurboVNC session after the
session is started. You can specify the window manager by passing
<code>-wm <em>window-manager</em></code> to <code>vncserver</code> or
setting <code>$wm=“<em>window-manager</em>”;</code> in
<strong class="filename">turbovncserver.conf</strong>, where
<em><code>window-manager</code></em> corresponds to a session desktop
file located in the X sessions directory
(<strong class="filename">/usr/share/xsessions</strong> or
<strong class="filename">/usr/local/share/xsessions</strong>) without
the <strong class="filename">.desktop</strong> extension. (For example,
pass <code>-wm xfce</code> to <code>vncserver</code> or set
<code>$wm="xfce";</code> in
<strong class="filename">turbovncserver.conf</strong> to launch the
window manager specified in
<strong class="filename">xfce.desktop</strong>.) If unspecified, the
window manager defaults to</p>
<ul class="Itemize">
<li class="Itemize-1 Itemize asterisk">
<code>gnome</code> if <strong class="filename">gnome.desktop</strong>
exists in the X sessions directory, or
</li>
<li class="Itemize-1 Itemize asterisk">
<code>ubuntu</code> if <strong class="filename">ubuntu.desktop</strong>
exists in the X sessions directory, or
</li>
<li class="Itemize-1 Itemize asterisk">
<code>mate</code> if <strong class="filename">mate.desktop</strong>
exists in the X sessions directory, or
</li>
<li class="Itemize-1 Itemize asterisk">
<code>xfce</code> if <strong class="filename">xfce.desktop</strong>
exists in the X sessions directory.
</li>
</ul>
<p>Specifying <code>2d</code> as the window manager launches GNOME Classic
or Flashback if <strong class="filename">gnome-classic.desktop</strong>
or <strong class="filename">gnome-flashback-metacity.desktop</strong>
exists in the X sessions directory.</p>
<p>The TurboVNC Server can run compositing window managers, such as GNOME
3+ or KDE 5+, using its <a href="#SoftwareOpenGL">built-in software
OpenGL implementation</a><a name="idx0026"></a>. However, for
performance reasons, it is recommended that GPU acceleration (with
<a href="#VGLWM">VirtualGL</a><a name="idx0027"></a> or
<a href="#DRI3">DRI3</a><a name="idx0028"></a>) be used with compositing
window managers. A non-compositing window manager such as MATE or Xfce
is recommended if GPU acceleration will not be used.</p>
<p>Refer to
<span class="remote"><a href="https://www.turbovnc.org/Documentation/Compatibility32" target="_blank" class="remote">this
report</a></span><a name="idx0029"></a> for an up-to-date list of window
managers that have been tested with this version of the TurboVNC Server,
how to configure the TurboVNC Server to use those window managers, and a
list of known compatibility issues.</p>
<h2 id="hd006004">6.4 Manually Connecting to a VNC Server</h2>
<h3 id="hd006004001">Procedure</h3>
<ol class="Ordered numeric">
<li class="Ordered-1 Ordered">
On the client machine, start the TurboVNC Viewer.
<dl class="Description">
<dt class="Description-3 Description">Linux/Un*x clients</dt>
<dd class="Description-3 Description">
Open a new terminal/xterm and type
<pre class="verbatim">
/opt/TurboVNC/bin/vncviewer
</pre>
</dd>
<dt class="Description-3 Description">Mac clients</dt>
<dd class="Description-3 Description">
Open the <strong class="filename">TurboVNC Viewer</strong> application,
located in the <strong class="filename">TurboVNC</strong> Applications
folder, or open a new terminal and type
<pre class="verbatim">
/opt/TurboVNC/bin/vncviewer
</pre>
</dd>
<dt class="Description-3 Description">Windows clients</dt>
<dd class="Description-3 Description">
Select <strong class="filename">TurboVNC Viewer</strong> in the
<strong class="filename">TurboVNC</strong> Start Menu group, or open a
new command prompt and type
<pre class="verbatim">
c:\Program Files\TurboVNC\vncviewer.bat
</pre>
</dd>
</dl>
</li>
<li class="Ordered-1 Ordered">
A small dialog box will appear. <br /><br />
<img src="newconn.png" alt="newconn" class="inline" id="imgid_3" name="imgid_3"/>
<br /><br /> Enter the X display name (hostname, or IP address, and
display number) of the VNC server or TurboVNC session in the “VNC
server” field, then click “Connect”.
</li>
<li class="Ordered-1 Ordered">
Another dialog box appears, prompting for the password (if Standard VNC
authentication is being used) or for the username and password (if Unix
Login authentication is being used.) <br /><br />
<div class="table">
<table class="standard">
<tr class="standard">
<td class="standard">Standard VNC Authentication Dialog</td>
<td class="standard"><img src="vncauth.png" alt="vncauth" class="inline" id="imgid_4" name="imgid_4"/></td>
</tr>
<tr class="standard">
<td class="standard">Unix Login Authentication Dialog</td>
<td class="standard"><img src="unixauth.png" alt="unixauth" class="inline" id="imgid_5" name="imgid_5"/></td>
</tr>
</table>
</div>
<br /> Enter the VNC server password or the Unix username/password and
press Enter. <br /><br /> A VNC desktop window should appear on your
client machine. This window contains a virtual desktop with which you
can interact to launch graphical applications on the VNC host.
<div class="important"><p class="important">
If you are connecting to a non-VeNCrypt-compatible VNC server, then the authentication dialog will warn you that the connection is not encrypted: <br /><br /> <img src="vncauth-insecure.png" alt="vncauth-insecure" class="inline" id="imgid_6" name="imgid_6"/> <br /><br /> You should never use Unix Login authentication with an unencrypted connection. Instead, tunnel the connection through SSH. (See Section <a href="#Secure_TurboVNC_Usage" class="ref">6.7</a> below for more details.)
</p></div>
</li>
</ol>
<h2 id="hd006005">6.5 Disconnecting and Killing a TurboVNC Session</h2>
<p>Closing the TurboVNC Viewer disconnects from the TurboVNC session, but
the TurboVNC session will remain running on the TurboVNC host (as will
any applications that you may have started within the session), and you
can reconnect to the session at any time.</p>
<p>If the TurboVNC session was created with default settings, then the
easiest way to kill it is to log out of the window manager running in
the session. You can also use the
<a href="#TurboVNC_Session_Manager">TurboVNC Session
Manager</a><a name="idx0030"></a> to remotely kill TurboVNC sessions, or
you can type the following command:</p>
<pre class="verbatim">/opt/TurboVNC/bin/vncserver -kill :<em>n</em></pre>
<p>from a terminal in the TurboVNC session or from an SSH session on the
host. Replace <em><code>n</code></em> with the X display number of the
TurboVNC session you want to kill.</p>
<p>To list the X display numbers and process ID’s of all TurboVNC
sessions currently running under your user account on a particular host,
type the following command:</p>
<pre class="verbatim">
/opt/TurboVNC/bin/vncserver -list
</pre>
<p>from a terminal in the TurboVNC session or from an SSH session on the
host.</p>
<h2 id="hd006006">6.6 Using TurboVNC in a Web Browser</h2>
<p><a name="noVNC"></a></p>
<p>When a TurboVNC session is started, the <code>vncserver</code> script
can optionally start a simple web server that serves up
<span class="remote"><a href="https://novnc.com" target="_blank" class="remote">noVNC</a></span><a name="idx0031"></a>,
an HTML 5/JavaScript VNC viewer that works in any web browser (with
reduced performance and features relative to the TurboVNC Viewer.) This
allows you to easily connect to a TurboVNC session from a machine that
does not have the TurboVNC Viewer installed (including mobile devices.)</p>
<p>To launch noVNC along with a TurboVNC session, pass <code>-novnc
<em>dir</em></code> to <code>vncserver</code> when starting the session,
where <em><code>dir</code></em> is the directory containing noVNC.
(Setting the <code>$noVNC</code> variable in
<strong class="filename">turbovncserver.conf</strong> has the same
effect.) The <code>vncserver</code> script will print the noVNC URL,
which will be of the form:</p>
<pre class="verbatim">http://<em>host</em>:<em>5800+n</em>/vnc.html?host=<em>host</em>&port=<em>5900+n</em></pre>
<p>or</p>
<pre class="verbatim">https://<em>host</em>:<em>5800+n</em>/vnc.html?host=<em>host</em>&port=<em>5900+n</em>&encrypt=1</pre>
<p>where <em><code>host</code></em> is the hostname or IP address of the
TurboVNC host and <em><code>n</code></em> is the X display number of the
TurboVNC session.</p>
<p>Point your web browser to that URL in order to access the TurboVNC
session. You can optionally pass <code>-x509cert
<em>certificate-file</em> -x509key <em>private-key-file</em></code> to
<code>vncserver</code> (or set the <code>$x509CertFile</code> and
<code>$x509KeyFile</code> variables in
<strong class="filename">turbovncserver.conf</strong>) to encrypt both
the HTTP and RFB connections. See the <code>vncserver</code> man page
for more details.</p>
<div class="important"><p class="important">
NOTE: noVNC only supports VNC Password authentication, so it is strongly recommended that it be used only with one-time passwords unless the connections are encrypted.
</p></div>
<h2 id="hd006007">6.7 Using SSH to Manually Secure a TurboVNC Connection</h2>
<p><a name="Secure_TurboVNC_Usage"></a></p>
<p>If the <a href="#TurboVNC_Session_Manager">TurboVNC Session
Manager</a><a name="idx0032"></a> is not being used, then the connection
between the TurboVNC Server and the TurboVNC Viewer will, by default,
use Anonymous TLS encryption. (Refer to Chapter
<a href="#Security_Extensions" class="ref">8</a>.) However, it may be
preferable to secure the TurboVNC connection using SSH rather than
Anonymous TLS encryption, particularly if one does not want to open
additional ports in the host’s firewall. This can easily be
accomplished using the TurboVNC Viewer’s <code>Tunnel</code> and
<code>Jump</code> parameters (or the equivalent GUI options, which are
located under the “Security” tab in the TurboVNC Viewer
Options dialog.)</p>
<p>The TurboVNC Viewer’s <code>Tunnel</code> and <code>Jump</code>
parameters take advantage of the port forwarding feature in SSH. For
instance, running</p>
<pre class="verbatim"><em>vncviewer</em> -tunnel <em>user</em>@<em>host</em>:<em>n</em></pre>
<p>is the equivalent of running</p>
<pre class="verbatim">ssh -L <em>fp</em>:localhost:<em>5900+n</em> <em>user</em>@<em>host</em>
<em>vncviewer</em> localhost::<em>fp</em></pre>
<p>where <em><code>fp</code></em> is a free TCP port on the client machine
(this is automatically determined by the TurboVNC Viewer.) Similarly,
running</p>
<pre class="verbatim"><em>vncviewer</em> -jump <em>jump-user</em>@<em>jump-host</em>:<em>jump-port</em> <em>vnc-user</em>@<em>vnc-host</em>:<em>n</em></pre>
<p>is the equivalent of running</p>
<pre class="verbatim">ssh -J <em>jump-user</em>@<em>jump-host</em>:<em>jump-port</em> -L <em>fp</em>:localhost:<em>5900+n</em> <em>vnc-user</em>@<em>vnc-host</em>
<em>vncviewer</em> localhost::<em>fp</em></pre>
<div class="important"><p class="important">
In the above examples, <em><code>vncviewer</code></em> is the command used to launch the TurboVNC Viewer– <code>/opt/TurboVNC/bin/vncviewer</code> on Linux/Un*x and Mac systems and <code>c:\Program Files\TurboVNC\vncviewer.bat</code> on Windows systems.
</p></div>
<div class="important"><p class="important">
When using the <code>Jump</code> parameter, the VNC host is specified from the point of view of the gateway host.
</p></div>
<h2 id="hd006008">6.8 Requiring SSH Tunneling</h2>
<p>Passing an argument of <code>-localhost</code> to <code>vncserver</code>
will force the TurboVNC session to accept inbound connections only from
the TurboVNC host. This effectively forces SSH tunneling to be used for
remote connections. If the <code>no-remote-connections</code> directive
is set in the TurboVNC security configuration file, then that has the
effect of enabling the <code>-localhost</code> option for all new
TurboVNC sessions that are started on the host.</p>
<p>Passing an argument of <code>-noreverse</code> to <code>vncserver</code>
will disable the ability to make outbound (reverse) connections from the
TurboVNC session. If the <code>no-reverse-connections</code> directive
is set in the TurboVNC security configuration file, then that has the
effect of enabling the <code>-noreverse</code> option for all new
TurboVNC sessions that are started on the host.</p>
<p>If the host is configured such that it only allows SSH connections, then
disallowing the TLS* security types on a system-wide basis (by setting
the <code>permitted-security-types</code> directive in the TurboVNC
security configuration file) is recommended. Otherwise, when using the
TurboVNC Viewer with default settings, the connection will have
redundant encryption.</p>
<p><img src="vncauth-redundant.png" alt="vncauth-redundant" class="inline" id="imgid_7" name="imgid_7"/></p>
<p>Note that only the OTP security type is needed when using the
<a href="#TurboVNC_Session_Manager">TurboVNC Session
Manager</a><a name="idx0033"></a> with its default settings.</p>
<h2 id="hd006009">6.9 Running OpenGL Applications</h2>
<p><a name="SoftwareOpenGL"></a></p>
<p>The TurboVNC Server includes a software GLX/OpenGL implementation that
can be used for casual 3D rendering. This implementation uses the
swrast DRI driver provided by Mesa 8.x and later, and it supports only
direct rendering. In general, if the TurboVNC host has a GPU, then you
should use <a href="#VGL">VirtualGL</a><a name="idx0034"></a> or
<a href="#DRI3">DRI3</a><a name="idx0035"></a> rather than relying on
TurboVNC’s software OpenGL implementation.</p>
<p>Passing <code>-extension GLX</code> to <code>vncserver</code>
disables the built-in GLX/OpenGL implementation, thus restoring the
behavior of TurboVNC 2.1.x and earlier (which required VirtualGL in
order to run OpenGL applications.) If the built-in GLX/OpenGL
implementation is not functioning properly, then pass
<code>-verbose</code> to <code>vncserver</code> to log informational
messages that may reveal the source of the problem.</p>
<h2 id="hd0060010">6.10 Further Reading</h2>
<p>For more detailed instructions on the usage of TurboVNC:</p>
<dl class="Description">
<dt class="Description-1 Description">TurboVNC Server</dt>
<dd class="Description-1 Description">
Refer to the TurboVNC man pages:
<pre class="verbatim">
man -M /opt/TurboVNC/man vncserver
man -M /opt/TurboVNC/man Xvnc
man -M /opt/TurboVNC/man vncconnect
man -M /opt/TurboVNC/man vncpasswd
man -M /opt/TurboVNC/man tvncconfig
</pre>
</dd>
<dt class="Description-1 Description">TurboVNC Viewer</dt>
<dd class="Description-1 Description">
Run
<pre class="verbatim">
/opt/TurboVNC/bin/vncviewer -?
</pre>
on Linux/Un*x and Mac systems or
<pre class="verbatim">
c:\Program Files\TurboVNC\vncviewer.bat -?
</pre>
on Windows systems to display a list of command-line options and
commonly-used parameters and their descriptions. Replace
<code>-?</code> with <code>-??</code> to display a list of advanced
parameters and their descriptions.
</dd>
</dl>
<p><br /></p>
<hr class="break" />
<h1 id="hd007"><a name="file007"></a>7 Performance and Image Quality</h1>
<p>The level of image compression in TurboVNC can be adjusted to balance
the (sometimes conflicting) goals of high image quality and high
performance. There are four options that control the manner in which
TurboVNC compresses images:</p>
<dl class="Description">
<dt class="Description-1 Description">Allow JPEG compression</dt>
<dd class="Description-1 Description">
If this option is enabled, then TurboVNC will use JPEG compression for
subrectangles that have a high number of unique colors, and it will use
indexed color subencoding for subrectangles that have a low number of
unique colors. If this option is disabled, then TurboVNC will select
between indexed color or raw subencoding, depending on the size of the
subrectangle and its color count.
</dd>
<dt class="Description-1 Description">JPEG image quality</dt>
<dd class="Description-1 Description">
Lower quality levels produce grainier JPEG images with more noticeable
compression artifacts, but lower quality levels also use less network
bandwidth and CPU time.
</dd>
<dt class="Description-1 Description">JPEG chrominance subsampling</dt>
<dd class="Description-1 Description">
When compressing an image using JPEG, the RGB pixels are first
converted to the YCbCr colorspace, a colorspace in which each pixel is
represented as a brightness (Y, or “luminance”) value and a
pair of color (Cb & Cr, or “chrominance”) values.
After this colorspace conversion, chrominance subsampling can be used
to discard some of the chrominance components in order to save
bandwidth. This works because the human eye is more sensitive to
changes in brightness than to changes in color. 1X subsampling (the
default in TurboVNC) retains the chrominance components for all pixels,
and thus it provides the best image quality but also uses the most
network bandwidth and CPU time. 2X subsampling retains the chrominance
components for every other pixel, and 4X subsampling retains the
chrominance components for every fourth pixel. (This is typically
implemented as 2X subsampling in both X and Y directions.) Grayscale
throws out all of the chrominance components, leaving only luminance.
2X and 4X subsampling typically produce noticeable blurring of lines
and other sharp features, but with photographic or other
“smooth” image content, it may be difficult to detect any
difference between 1X, 2X, and 4X.
</dd>
<dt class="Description-1 Description">Compression level</dt>
<dd class="Description-1 Description">
In TurboVNC, the compression level specifies:
<ol class="Ordered numeric"><li class="Ordered-0">
the level of zlib compression that will be used with indexed color,
mono, and raw subrectangles
</li>
<li class="Ordered-0">
the “palette threshold” (the minimum number of colors
that a
subrectangle must have before it is encoded as JPEG or raw instead
of
indexed color)
</li>
<li class="Ordered-0">
whether or not <a href="#InterframeComparison">interframe
comparison</a><a name="idx0036"></a> should be used
</li></ol> See Section
<a href="#AdvancedCompression" class="ref">7.2</a> below for more
details.
</dd>
</dl>
<p>These parameters can be adjusted by accessing the TurboVNC Viewer
Options dialog box. (Click on the “Options” button in the
New TurboVNC Connection dialog box or, after connecting to the server,
click on the Connection Options button in the toolbar.)</p>
<p>The TurboVNC Viewer provides five preset “encoding methods”
corresponding to the most useful combinations of the image compression
options described above:</p>
<a name="tab007001"></a>
<div class="table">
<table class="standard" summary="TurboVNC Encoding Methods">
<caption>Table 7.1: TurboVNC Encoding Methods</caption>
<thead class="standard">
<tr class="head ">
<th class="head standard">Encoding method</th>
<th class="head standard">Allow JPEG</th>
<th class="head standard">JPEG image quality</th>
<th class="head standard">JPEG chrominance subsampling</th>
<th class="head standard">Compression level</th>
<th class="head standard">Notes</th>
</tr>
</thead>
<tr class="standard">
<td class="standard">“Tight + Perceptually Lossless JPEG”</td>
<td class="standard">Yes</td>
<td class="standard">95</td>
<td class="standard">1x</td>
<td class="standard">1</td>
<td class="standard">This encoding method should be perceptually lossless (that is, any image compression artifacts it produces should be imperceptible to human vision) under most viewing conditions. This encoding method requires a great deal of network bandwidth, however, and is generally not recommended except on 50 Megabit/second and faster networks.</td>
</tr>
<tr class="standard">
<td class="standard">“Tight + Medium-Quality JPEG”</td>
<td class="standard">Yes</td>
<td class="standard">80</td>
<td class="standard">2x</td>
<td class="standard">6</td>
<td class="standard">For subrectangles that have a high number of unique colors, this encoding method produces some minor, but generally not very noticeable, image compression artifacts. All else being equal, this encoding method typically uses about twice the network bandwidth of the “Tight + Low-Quality JPEG” encoding method and about half the bandwidth of the “Tight + Perceptually Lossless JPEG” encoding method, making it appropriate for medium-speed networks such as 10 Megabit Ethernet. Interframe comparison is enabled with this encoding method. (Compression Level 6 = Compression Level 1 + interframe comparison.)</td>
</tr>
<tr class="standard">
<td class="standard">“Tight + Low-Quality JPEG”</td>
<td class="standard">Yes</td>
<td class="standard">30</td>
<td class="standard">4x</td>
<td class="standard">7</td>
<td class="standard">For subrectangles that have a high number of unique colors, this encoding method produces very noticeable image compression artifacts. However, it performs optimally on low-bandwidth connections. If image quality is more critical than performance, then use one of the other encoding methods or take advantage of the <a href="#LR">Lossless Refresh feature</a><a name="idx0037"></a>. In addition to reducing the JPEG quality to a “minimum usable” level, this encoding method also enables interframe comparison and Compression Level 2. (CL 7 = CL 2 + interframe comparison.) Compression Level 2 can reduce network usage for low-color application workloads that are not good candidates for JPEG compression.</td>
</tr>
<tr class="standard">
<td class="standard">“Lossless Tight”</td>
<td class="standard">No</td>
<td class="standard">N/A</td>
<td class="standard">N/A</td>
<td class="standard">0</td>
<td class="standard">This encoding method uses indexed color subencoding for subrectangles that have a low number of unique colors and raw subencoding for subrectangles that have a high number of unique colors. If the VNC viewer supports the “Tight Encoding Without Zlib” RFB extension, then zlib is bypassed, and all subrectangles are sent without compression. Otherwise, all subrectangles are “compressed” using zlib with zlib compression level 0. (Zlib compression level 0 maintains the zlib state but does not perform any actual compression. However, the overhead of maintaining the zlib state reduces overall Tight encoding performance by 10-60% vs. bypassing zlib, depending on the zlib implementation.) Lossless Tight uses significantly less CPU time than any of the JPEG-based encoding methods, but it is suitable only for gigabit and faster networks.</td>
</tr>
<tr class="standard">
<td class="standard">“Lossless Tight + Zlib”</td>
<td class="standard">No</td>
<td class="standard">N/A</td>
<td class="standard">N/A</td>
<td class="standard">6</td>
<td class="standard">This encoding method uses indexed color subencoding for subrectangles that have a low number of unique colors and raw subencoding for subrectangles that have a high number of unique colors. It compresses all subrectangles using zlib with zlib compression level 1. For certain types of low-color workloads (CAD applications, in particular), this encoding method may use less network bandwidth than the “Tight + Perceptually Lossless JPEG” encoding method, but it also uses significantly more CPU time than any of the JPEG-based encoding methods. Interframe comparison is enabled with this encoding method. (Compression Level 6 = Compression Level 1 + interframe comparison.)</td>
</tr>
</table>
</div>
<p>The encoding method can be set in the TurboVNC Viewer Options dialog
box. (Click on the “Options” button in the New TurboVNC
Connection dialog box or, after connecting to the server, click on the
Connection Options button in the toolbar.)</p>
<h2 id="hd007001">7.1 Interframe Comparison</h2>
<p><a name="InterframeComparison"></a></p>
<p>Certain ill-behaved applications can sometimes draw the same thing over
and over again, and this can cause redundant framebuffer updates to be
sent to the VNC viewer. Additionally, modern GUI toolkits often use
image-based drawing methods (the X Rendering Extension, for instance),
which can result in an entire window being redrawn even if only a few
pixels in the window have changed. The TurboVNC Server can guard
against this by maintaining a copy of the remote framebuffer for each
connected viewer, comparing each new framebuffer update rectangle
against the pixels in the framebuffer copy, and discarding any redundant
portions of the rectangle before they are sent to the viewer.</p>
<p>Interframe comparison has some tradeoffs. Perhaps the most important of
these is that it increases the memory usage of the TurboVNC Server by a
factor of N, where N is the number of connected viewers. This can prove
to be quite significant if the remote desktop size is relatively large.
2D applications are most often the ones that generate duplicate
framebuffer updates, so using interframe comparison with such
applications can significantly reduce the network usage and the host CPU
usage (since fewer rectangles are actually being encoded.) However,
with 3D applications, the benefits of interframe comparison are less
clear, since it is less common for those applications to generate
duplicate framebuffer updates. Interframe comparison may benefit
certain classes of 3D applications, such as design applications that
render a model against a static background– particularly when the
model is not zoomed in enough to fill the entire window. In real-world
tests, however, interframe comparison rarely reduces the network usage
for 3D applications by more than 5-10%. Furthermore, with games and
other immersive applications that modify most of the pixels on the
screen each time a frame is rendered, interframe comparison can actually
increase both CPU usage and network usage. Furthermore, the effects of
duplicate framebuffer updates are not typically noticeable on high-speed
networks, but an increase in host CPU usage might be.</p>
<p>For these reasons, interframe comparison is not enabled by default and
should not generally be enabled except on bandwidth-constrained networks
and with applications for which it can be shown to be beneficial.
Interframe comparison can be enabled by passing an argument of
<code>-interframe</code> to <code>vncserver</code> when starting a
TurboVNC session, by using <code>tvncconfig</code> to set the
<code>Interframe</code> parameter for a running TurboVNC session, or by
requesting a compression level of 5 or higher from the viewer (see
below.)</p>
<h2 id="hd007002">7.2 Advanced Compression Options</h2>
<p><a name="AdvancedCompression"></a></p>
<p>One of the underlying principles of TurboVNC’s design is to expose
only the options that have proven to be useful (that is, the options
that have proven to have good performance tradeoffs.) Thus, the
TurboVNC Viewer Options dialog normally only allows you to select
Compression Levels 1-2 if JPEG subencoding is enabled (6-7 if interframe
comparison is also enabled) or Compression Levels 0-1 if JPEG
subencoding is disabled (5-6 if interframe comparison is enabled.) Other
compression levels can, however, be specified using the TurboVNC
Viewer’s <code>CompressLevel</code> parameter, and doing so will
enable a compatibility mode in the TurboVNC Viewer Options dialog that
allows any compression level from 0 to 9 to be requested.</p>
<p>When connected to a TurboVNC session, requesting a particular
compression level has the following effect:</p>
<a name="tab007002"></a>
<div class="table">
<table class="standard" summary="Compression Levels Supported by the TurboVNC Server (JPEG Enabled)">
<caption>Table 7.2: Compression Levels Supported by the TurboVNC Server (JPEG Enabled)</caption>
<thead class="standard">
<tr class="head ">
<th class="head standard">Compression level</th>
<th class="head standard">Zlib compression level (non-JPEG subrectangles)</th>
<th class="head standard">Palette threshold</th>
<th class="head standard">Interframe comparison</th>
<th class="head standard">Notes</th>
</tr>
</thead>
<tr class="standard">
<td class="standard">0</td>
<td class="standard">1</td>
<td class="standard">24</td>
<td class="standard">No</td>
<td class="standard">Same as Compression Level 1. Bypassing zlib when JPEG is enabled would only reduce the CPU usage for non-JPEG subrectangles, which is of limited usefulness. Furthermore, bypassing zlib requires an RFB protocol extension that is not supported by non-TurboVNC viewers (as of this writing.) It is presumed that, if one wants to reduce the CPU usage, then one wants to do so for all subrectangles, so CL 0 without JPEG (AKA “Lossless Tight”) should be used.</td>
</tr>
<tr class="standard">
<td class="standard">1</td>
<td class="standard">1</td>
<td class="standard">24</td>
<td class="standard">No</td>
<td class="standard">See the description of the “Tight + JPEG” encoding methods above.</td>
</tr>
<tr class="standard">
<td class="standard">2</td>
<td class="standard">3</td>
<td class="standard">96</td>
<td class="standard">No</td>
<td class="standard">A higher palette threshold causes indexed color subencoding to be used more often than with CL 1, and indexed color subrectangles are compressed using a higher zlib compression level. This can provide typically 20-40% better compression than CL 1 (with a commensurate increase in CPU usage) for workloads that have a low number of unique colors. However, Compression Level 2 can increase the CPU usage for some high-color workloads without providing significantly better compression.</td>
</tr>
<tr class="standard">
<td class="standard">3-4</td>
<td class="standard">3</td>
<td class="standard">96</td>
<td class="standard">No</td>
<td class="standard">Same as Compression Level 2 (reserved for future expansion)</td>
</tr>
<tr class="standard">
<td class="standard">5-6</td>
<td class="standard">1</td>
<td class="standard">24</td>
<td class="standard">Yes</td>
<td class="standard">Same as Compression Level 1 but with interframe comparison enabled</td>
</tr>
<tr class="standard">
<td class="standard">7-8</td>
<td class="standard">3</td>
<td class="standard">96</td>
<td class="standard">Yes</td>
<td class="standard">Same as Compression Level 2 but with interframe comparison enabled</td>
</tr>
<tr class="standard">
<td class="standard">9</td>
<td class="standard">7</td>
<td class="standard">256</td>
<td class="standard">Yes</td>
<td class="standard">This mode is included only for backward compatibility with TightVNC. It provides approximately the same level of compression for 2D applications as Compression Level 9 in TightVNC 1.3.x while using much less CPU time. It also provides much better compression than TightVNC for 3D and video applications. However, relative to Compression Level 2, this mode uses approximately twice as much CPU time and only achieves about 10-20% better average compression for 2D applications (and has no noticeable benefit for 3D and video applications.) Thus, its usefulness is generally very limited.</td>
</tr>
</table>
</div>
<p></p>
<a name="tab007003"></a>
<div class="table">
<table class="standard" summary="Compression Levels Supported by the TurboVNC Server (JPEG Disabled)">
<caption>Table 7.3: Compression Levels Supported by the TurboVNC Server (JPEG Disabled)</caption>
<thead class="standard">
<tr class="head ">
<th class="head standard">Compression Level</th>
<th class="head standard">Zlib compression level (indexed color subrectangles)</th>
<th class="head standard">Zlib compression level (raw subrectangles)</th>
<th class="head standard">Palette threshold</th>
<th class="head standard">Interframe comparison</th>
<th class="head standard">Notes</th>
</tr>
</thead>
<tr class="standard">
<td class="standard">0</td>
<td class="standard">None</td>
<td class="standard">None</td>
<td class="standard">Subrectangle size / 4</td>
<td class="standard">No</td>
<td class="standard">See the description of the “Lossless Tight” encoding method above.</td>
</tr>
<tr class="standard">
<td class="standard">1</td>
<td class="standard">1</td>
<td class="standard">1</td>
<td class="standard">Subrectangle size / 96</td>
<td class="standard">No</td>
<td class="standard">See the description of the “Lossless Tight + Zlib” encoding method above.</td>
</tr>
<tr class="standard">
<td class="standard">2-4</td>
<td class="standard">1</td>
<td class="standard">1</td>
<td class="standard">Subrectangle size / 96</td>
<td class="standard">No</td>
<td class="standard">Same as Compression Level 1 (reserved for future expansion)</td>
</tr>
<tr class="standard">
<td class="standard">5</td>
<td class="standard">None</td>
<td class="standard">None</td>
<td class="standard">Subrectangle size / 4</td>
<td class="standard">Yes</td>
<td class="standard">Same as Compression Level 0 but with interframe comparison enabled</td>
</tr>
<tr class="standard">
<td class="standard">6-8</td>
<td class="standard">1</td>
<td class="standard">1</td>
<td class="standard">Subrectangle size / 96</td>
<td class="standard">Yes</td>
<td class="standard">Same as Compression Level 1 but with interframe comparison enabled</td>
</tr>
<tr class="standard">
<td class="standard">9</td>
<td class="standard">7</td>
<td class="standard">5</td>
<td class="standard">Subrectangle size / 96</td>
<td class="standard">Yes</td>
<td class="standard">This mode is included only for backward compatibility with TightVNC. It provides approximately the same level of compression for 2D applications as Compression Level 9 in TightVNC 1.3.x, while using much less CPU time. It also provides much better compression than TightVNC for 3D and video applications. However, relative to Compression Level 1, this mode uses approximately twice as much CPU time and only achieves about 10% better average compression for 2D applications (and has no noticeable benefit for 3D and video applications.) Thus, its usefulness is generally very limited.</td>
</tr>
</table>
</div>
<h2 id="hd007003">7.3 Lossless Refresh</h2>
<p><a name="LR"></a></p>
<p>Since both of TurboVNC’s mathematically lossless encoding methods
have performance drawbacks, another option for image-quality-critical
applications is the Lossless Refresh feature. When a lossless refresh
is requested by a TurboVNC viewer, the VNC server will send a
mathematically lossless image of the remote desktop to the requesting
viewer. A user could, for instance, use the “Tight + Low-Quality
JPEG” encoding method on a low-bandwidth network to improve the
performance of rotating/panning/zooming an object in a 3D application,
then the user could request a lossless refresh when they are ready to
interpret or analyze the object.</p>
<p>To perform a lossless refresh, press CTRL-ALT-SHIFT-L or click on the
Lossless Refresh toolbar icon.</p>
<h2 id="hd007004">7.4 Automatic Lossless Refresh</h2>
<p><a name="ALR"></a></p>
<p>Passing an argument of <code>-alr <em>timeout</em></code> to
<code>vncserver</code> (or using <code>tvncconfig</code> to set the
<code>ALR</code> parameter for a running TurboVNC session) enables the
Automatic Lossless Refresh (ALR) feature for the TurboVNC session. ALR
monitors all of the VNC viewer connections, and if more than
<em><code>timeout</code></em> seconds have elapsed since the last
framebuffer update was sent to a given viewer, then the TurboVNC Server
sends that viewer a mathematically lossless copy of any
“ALR-eligible” screen regions that have been affected by
lossy compression. You can also pass arguments of <code>-alrqual</code>
and <code>-alrsamp</code> to <code>vncserver</code> (or use
<code>tvncconfig</code> to set the <code>ALRQual</code> and
<code>ALRSamp</code> parameters for a running TurboVNC session) to
specify that automatic lossless refreshes should be sent using JPEG
instead. (See the <code>Xvnc</code> man page for details.)</p>
<p>The ALR feature is designed mainly for use with interactive
visualization applications. The idea is that, on a low-bandwidth
connection, low-quality JPEG can be used while the 3D scene is
rotated/panned/zoomed, but when the motion stops, a fully lossless copy
of the 3D image is sent and can be studied in detail.</p>
<p>The default is for any regions drawn with <code>X[Shm]PutImage()</code>
to be ALR-eligible– as well as any regions drawn with CopyRect, if
the source of the CopyRect operation was affected by lossy compression.
(CopyRect is an RFB encoding that allows the VNC server to request that
a VNC viewer move a rectangle of pixels from one location to another.)
When used with VirtualGL, this means that ALRs will mainly just be sent
for the OpenGL-rendered regions of the remote desktop. That should be
fine for most 3D applications, since the OpenGL-rendered regions are the
ones that are quality-critical. The default ALR behavior also prevents
what might best be called the “blinking cursor dilemma.”
Certain programs have a blinking cursor that may update more frequently
than the ALR timeout. Since an ALR is triggered based on a period of
inactivity relative to the last framebuffer update, these frequent
updates prevent an ALR from ever being sent. Fortunately, blinking
cursors are not typically drawn using <code>X[Shm]PutImage()</code>, so
the problem is effectively worked around by limiting the ALR-eligible
regions to just the subset of regions that were drawn using
<code>X[Shm]PutImage()</code> and CopyRect.</p>
<div class="important"><p class="important">
NOTE: Ill-behaved applications that continuously render the same image will cause a variation of the “blinking cursor dilemma” and thus defeat ALR unless <a href="#InterframeComparison">interframe comparison</a><a name="idx0038"></a> is enabled.
</p></div>
<p>You can override the default ALR behavior, thus making all screen
regions eligible for ALR, by setting the <code>TVNC_ALRALL</code>
environment variable to <code>1</code> on the TurboVNC host prior to
starting a TurboVNC session or by using <code>tvncconfig</code> to set
the <code>ALRAll</code> parameter for a running TurboVNC session.</p>
<h2 id="hd007005">7.5 Multithreading</h2>
<p><a name="Multithreading"></a></p>
<p>By default, the TurboVNC Server uses multiple threads to perform image
encoding and compression, thus allowing it to take advantage of
multi-core or multi-processor systems. The server splits the screen
vertically into N tiles, where N is the number of threads, and assigns
each tile to a separate thread. The scalability of this algorithm is
nearly linear when used with demanding 3D or video applications that
fill most of the screen. However, whether or not multithreading
improves the overall performance of TurboVNC depends largely on the
performance of the viewer and the network. If either the viewer or the
network is the primary performance bottleneck, then enabling
multithreading in the server will not help. Multithreading is also not
currently implemented with non-Tight encoding types.</p>
<p>To disable server-side multithreading, set the <code>TVNC_MT</code>
environment variable to <code>0</code> on the host prior to starting
<code>vncserver</code>, or pass an argument of <code>-nomt</code> to
<code>vncserver</code>. The default behavior is to use as many threads
as there are cores on the TurboVNC host (up to a maximum of 4), but you
can set the <code>TVNC_NTHREADS</code> environment variable or pass an
argument of <code>-nthreads</code> to <code>vncserver</code> to override
this.</p>
<p><br /></p>
<hr class="break" />
<h1 id="hd008"><a name="file008"></a>8 TurboVNC Security Extensions</h1>
<p><a name="Security_Extensions"></a></p>
<h2 id="hd008001">8.1 Terminology</h2>
<p>In an attempt to be consistent with other VNC implementations, TurboVNC
uses the following terminology when referring to its security extensions:</p>
<dl class="Description">
<dt class="Description-1 Description">Authentication Method</dt>
<dd class="Description-1 Description">
A technique that the VNC server uses to validate authentication
credentials sent from a VNC viewer. If the credentials sent from a
particular VNC viewer are not valid, then that viewer is not allowed to
connect.
</dd>
<dt class="Description-1 Description">Authentication Scheme</dt>
<dd class="Description-1 Description">
A protocol used to send authentication credentials from a VNC viewer to
a VNC server for validation. Some authentication schemes are required
by the RFB protocol specification, and others are implemented as
extensions to that specification.
</dd>
<dt class="Description-1 Description">Encryption Method</dt>
<dd class="Description-1 Description">
A technique used to encrypt the data sent between the VNC server and
the VNC viewer
</dd>
<dt class="Description-1 Description">Security Type</dt>
<dd class="Description-1 Description">
A specific combination of an authentication method, an authentication
scheme, and an encryption method
</dd>
</dl>
<h2 id="hd008002">8.2 TurboVNC Server Authentication Methods</h2>
<dl class="Description">
<dt class="Description-1 Description">No Authentication</dt>
<dd class="Description-1 Description">
The VNC server does not authenticate the VNC viewer at all.
</dd>
<dt class="Description-1 Description">VNC Password Authentication</dt>
<dd class="Description-1 Description">
A session password sent from the VNC viewer is validated against a
password file, which is typically located under the user’s home
directory on the VNC host. The VNC password is separate from any other
login credentials and thus represents less of a security threat if
compromised (that is, assuming the VNC password and the user’s
account password are not the same.)
</dd>
<dt class="Description-1 Description">One-Time Password (OTP) Authentication</dt>
<dd class="Description-1 Description">
Using the <code>vncpasswd</code> program, a unique password is
generated “on the fly” for the TurboVNC session, and the
password is printed on the command line. (See the
<code>vncpasswd</code> man page for more details.) The user enters
this password into the VNC viewer, and the VNC viewer sends the
password to the server as if it were a VNC password. However, once the
OTP has been used to authenticate a viewer, the OTP is forgotten and
cannot be reused. OTP authentication can be used, for instance, to
launch or connect to TurboVNC sessions from an automated web portal or
from a job scheduler. OTP authentication is also useful for allowing
temporary access to a TurboVNC session for collaboration purposes. The
<a href="#TurboVNC_Session_Manager">TurboVNC Session
Manager</a><a name="idx0039"></a> uses OTP authentication by default,
which allows it to securely authenticate with a TurboVNC session
without prompting for additional credentials.
</dd>
<dt class="Description-1 Description">PAM User/Password Authentication</dt>
<dd class="Description-1 Description">
The VNC server uses Pluggable Authentication Modules (PAM) to validate
a username and password received from a VNC viewer. The password
received from the VNC viewer need not necessarily be validated against
the user’s account password. Generally, the TurboVNC Server can
validate the username and password using any authentication credentials
that can be accessed through PAM. Since the user/password
authentication schemes supported by TurboVNC (see below) transmit the
password from the VNC viewer to the VNC server as plain text, it is
strongly recommended that the PAM User/Password authentication method
be used only with session encryption or if the session is restricted to
allow only loopback (SSH) connections and to disallow reverse
connections (see Section
<a href="#Secure_TurboVNC_Usage" class="ref">6.7</a>.)
</dd>
</dl>
<h2 id="hd008003">8.3 TurboVNC Viewer Authentication Schemes</h2>
<dl class="Description">
<dt class="Description-1 Description">None</dt>
<dd class="Description-1 Description">
No authentication credentials are sent to the server.
</dd>
<dt class="Description-1 Description">Standard VNC Authentication</dt>
<dd class="Description-1 Description">
A password is sent to the server using a DES-encrypted
challenge/response scheme. The password can be up to 8 characters
long, so the DES key length is 56 bits. This is not a particularly
strong form of encryption by today’s standards. (56-bit DES was
broken by brute force attack in the late 1990s.)
</dd>
<dt class="Description-1 Description">Unix Login/Plain Authentication</dt>
<dd class="Description-1 Description">
Both the username and password are sent to the VNC server as plain
text. Thus, it is <em>strongly</em> recommended that this
authentication scheme be used only with VNC connections that are
encrypted using TLS (see below) or SSH (see Section
<a href="#Secure_TurboVNC_Usage" class="ref">6.7</a>.) Per the RFB
spec, this authentication scheme is referred to as “Unix
Login” when used with a TightVNC-compatible server and
“Plain” when used with a VeNCrypt-compatible server.
</dd>
</dl>
<h2 id="hd008004">8.4 Supported Encryption Methods</h2>
<p>TurboVNC supports three encryption methods:</p>
<dl class="Description">
<dt class="Description-1 Description">None</dt>
<dd class="Description-1 Description">
No encryption
</dd>
<dt class="Description-1 Description">Anonymous TLS Encryption</dt>
<dd class="Description-1 Description">
The connection is encrypted using TLS (Transport Layer Security)
without authentication (i.e. without a certificate.)
</dd>
<dt class="Description-1 Description">TLS/X.509 Encryption</dt>
<dd class="Description-1 Description">
The connection is encrypted using TLS with a specified X.509
certificate.
</dd>
</dl>
<h2 id="hd008005">8.5 Supported Security Types</h2>
<p>TurboVNC supports the following security types:</p>
<div class="table">
<table class="standard">
<thead class="standard">
<tr class="head ">
<th class="head standard">Server Security Type</th>
<th class="head standard">Authentication Method</th>
<th class="head standard">Encryption Method</th>
<th class="head standard">Viewer Security Type</th>
<th class="head standard">Authentication Scheme</th>
<th class="head standard">Compatibility</th>
</tr>
</thead>
<tr class="standard">
<td class="high standard">None</td>
<td class="standard">None</td>
<td class="standard">None</td>
<td class="high standard">None</td>
<td class="standard">None</td>
<td class="standard">RFB 3.3+</td>
</tr>
<tr class="standard">
<td class="high standard">VNC</td>
<td class="standard">VNC Password</td>
<td class="standard">None</td>
<td class="high standard" rowspan="2">VNC</td>
<td class="standard" rowspan="2">Standard VNC</td>
<td class="standard" rowspan="2">RFB 3.3+</td>
</tr>
<tr class="standard">
<td class="high standard">OTP</td>
<td class="standard">One-Time Password</td>
<td class="standard">None</td>
</tr>
<tr class="standard">
<td class="high standard">Plain</td>
<td class="standard">PAM User/Password</td>
<td class="standard">None</td>
<td class="high standard">Plain</td>
<td class="standard">Plain</td>
<td class="standard">RFB 3.7+ with VeNCrypt extensions</td>
</tr>
<tr class="standard">
<td class="high standard">TLSNone</td>
<td class="standard">None</td>
<td class="standard">Anonymous TLS</td>
<td class="high standard">TLSNone</td>
<td class="standard">None</td>
<td class="standard">RFB 3.7+ with VeNCrypt extensions</td>
</tr>
<tr class="standard">
<td class="high standard">TLSVnc</td>
<td class="standard">VNC Password</td>
<td class="standard">Anonymous TLS</td>
<td class="high standard" rowspan="2">TLSVnc</td>
<td class="standard" rowspan="2">Standard VNC</td>
<td class="standard" rowspan="2">RFB 3.7+ with VeNCrypt extensions</td>
</tr>
<tr class="standard">
<td class="high standard">TLSOtp</td>
<td class="standard">One-Time Password</td>
<td class="standard">Anonymous TLS</td>
</tr>
<tr class="standard">
<td class="high standard">TLSPlain</td>
<td class="standard">PAM User/Password</td>
<td class="standard">Anonymous TLS</td>
<td class="high standard">TLSPlain</td>
<td class="standard">Plain</td>
<td class="standard">RFB 3.7+ with VeNCrypt extensions</td>
</tr>
<tr class="standard">
<td class="high standard">X509None</td>
<td class="standard">None</td>
<td class="standard">TLS/X.509</td>
<td class="high standard">X509None</td>
<td class="standard">None</td>
<td class="standard">RFB 3.7+ with VeNCrypt extensions</td>
</tr>
<tr class="standard">
<td class="high standard">X509Vnc</td>
<td class="standard">VNC Password</td>
<td class="standard">TLS/X.509</td>
<td class="high standard" rowspan="2">X509Vnc</td>
<td class="standard" rowspan="2">Standard VNC</td>
<td class="standard" rowspan="2">RFB 3.7+ with VeNCrypt extensions</td>
</tr>
<tr class="standard">
<td class="high standard">X509Otp</td>
<td class="standard">One-Time Password</td>
<td class="standard">TLS/X.509</td>
</tr>
<tr class="standard">
<td class="high standard">X509Plain</td>
<td class="standard">PAM User/Password</td>
<td class="standard">TLS/X.509</td>
<td class="high standard">X509Plain</td>
<td class="standard">Plain</td>
<td class="standard">RFB 3.7+ with VeNCrypt extensions</td>
</tr>
<tr class="standard">
<td class="high standard">UnixLogin</td>
<td class="standard">PAM User/Password</td>
<td class="standard">None</td>
<td class="high standard">UnixLogin</td>
<td class="standard">Unix Login</td>
<td class="standard">RFB 3.7+ with TightVNC extensions</td>
</tr>
</table>
</div>
<div class="important"><p class="important">
NOTE: The security type names are case-insensitive. The capitalization conventions above are used for consistency with the RFB protocol specification.
</p></div>
<h2 id="hd008006">8.6 Enabling Security Types</h2>
<p>The default behavior of the TurboVNC Server is for all security types
except TLSNone, X509None, and None to be enabled and for VNC Password
and OTP authentication to be preferred over PAM User/Password
authentication. However, the system administrator can disable one or
more of the security types or change their preferred order by editing
the TurboVNC security configuration file. See the <code>Xvnc</code> man
page for more details. Note that only the OTP security type is needed
when using the <a href="#TurboVNC_Session_Manager">TurboVNC Session
Manager</a><a name="idx0040"></a> with its default settings.</p>
<p>If the VNC server allows multiple security types, then the TurboVNC
Viewer’s default security type will be determined by the
server’s preferred security type. In this case, the user can
override the default by using the TurboVNC Viewer’s
<code>SecurityTypes</code>, <code>User</code>, and
<code>NoUnixLogin</code> parameters. If the VNC server prefers a
security type that supports Standard VNC authentication, then the user
can force the use of Unix Login/Plain authentication by setting the
TurboVNC Viewer’s <code>User</code> parameter to
<em><code>user-name</code></em> when connecting to the VNC server.
Similarly, if the VNC server prefers a security type that supports Unix
Login/Plain authentication, then the user can force the use of Standard
VNC authentication by setting the <code>NoUnixLogin</code> parameter.
The same thing can also be accomplished by unchecking specific security
types in the “Security” tab of the TurboVNC Viewer Options
dialog or by using the <code>SecurityTypes</code> parameter to limit the
available security types or change their preferred order.</p>
<p>If the system administrator has not restricted any of the server
security types on a system-wide basis, then the user can disable some of
them, or change their preferred order, for a particular TurboVNC session
by using the <code>-securitytypes</code> command-line argument when
starting the session (or by setting the <code>$securityTypes</code>
variable in <strong class="filename">turbovncserver.conf</strong>.) See
the <code>Xvnc</code> man page for more details.</p>
<h2 id="hd008007">8.7 Further Reading</h2>
<p>For more detailed information about the TurboVNC security extensions,
refer to the TurboVNC man pages:</p>
<pre class="verbatim">
man -M /opt/TurboVNC/man vncserver
man -M /opt/TurboVNC/man Xvnc
man -M /opt/TurboVNC/man vncpasswd
</pre>
<p><br /></p>
<hr class="break" />
<h1 id="hd009"><a name="file009"></a>9 GPU-Accelerated OpenGL (Using VirtualGL with TurboVNC)</h1>
<p><a name="VGL"></a></p>
<p>Referring to the VirtualGL User’s Guide, VirtualGL’s X11
Transport draws OpenGL-rendered frames to an X display using standard
X11 drawing commands. Since this results in the frames being sent
uncompressed to the X server, the X11 Transport is designed to be used
with an “X proxy.” An X proxy acts as a virtual X server,
receiving X11 commands from applications (and from VirtualGL), rendering
the X11 commands into images, compressing the resulting images, and
sending the compressed images over the network to a client or clients.</p>
<p>Since VirtualGL sends rendered frames to the X proxy at a very fast
rate, the X proxy must be able to compress the frames very quickly in
order to keep up. When VirtualGL was first released, most X proxies
couldn’t. They simply weren’t designed to compress, with
any degree of performance, the large and complex images generated by 3D
applications. Enter TurboVNC. Although TurboVNC can be used with all
types of applications, it was initially designed as a fast X proxy for
VirtualGL. TurboVNC provides an alternate means of delivering rendered
frames from VirtualGL to a client machine without using
VirtualGL’s built-in VGL Transport.</p>
<h3 id="hd009000001">Advantages of TurboVNC (when compared to the VGL Transport)</h3>
<ul class="Itemize">
<li class="Itemize-1 Itemize asterisk">
When using the VGL Transport, non-OpenGL elements of the 3D
application’s GUI are sent over the network using remote X11,
which does not perform well on high-latency networks such as broadband
or long-haul fibre. On such networks, non-OpenGL elements of the 3D
application’s GUI will load and render much faster (perhaps even
orders of magnitude faster) with TurboVNC than with the VGL Transport.
</li>
<li class="Itemize-1 Itemize asterisk">
For 3D applications whose rendered frames do not contain very many
unique colors (for instance, CAD applications in wireframe mode), the
hybrid encoding methods used by TurboVNC generally require less network
bandwidth than the pure JPEG encoding method used by the VGL Transport.
</li>
<li class="Itemize-1 Itemize asterisk">
TurboVNC provides two lossless compression modes, one of which is
designed to reduce host CPU usage on gigabit networks and the other of
which is designed to provide reasonable performance on wide-area
networks (at the expense of higher host CPU usage.) The VGL
Transport’s only lossless option is uncompressed RGB.
</li>
<li class="Itemize-1 Itemize asterisk">
TurboVNC includes a Lossless Refresh feature that will, automatically
(during periods of inactivity) or on demand, send a mathematically
lossless copy of remote desktop regions that were previously sent using
lossy compression. Refer to Sections <a href="#LR" class="ref">7.3</a>
and Section <a href="#ALR" class="ref">7.4</a>.
</li>
<li class="Itemize-1 Itemize asterisk">
TurboVNC provides rudimentary collaboration capabilities. Multiple
users can simultaneously view the same TurboVNC session and pass around
control of the keyboard and mouse.
</li>
<li class="Itemize-1 Itemize asterisk">
From the point of view of the 3D application, the TurboVNC session is
stateless. If the network hiccups or the viewer is otherwise
disconnected, then the TurboVNC session continues to run on the host and
can be rejoined from any machine on the network.
</li>
<li class="Itemize-1 Itemize asterisk">
No X server is required on the client machine. This reduces the
deployment complexity for Windows clients.
</li>
<li class="Itemize-1 Itemize asterisk">
Any machine with a web browser, and any mobile device, can be used as a
TurboVNC client (with reduced performance and features relative to the
TurboVNC Viewer.) Refer to Section <a href="#noVNC" class="ref">6.6</a>.
</li>
</ul>
<h3 id="hd009000002">Disadvantages of TurboVNC (when compared to the VGL transport)</h3>
<ul class="Itemize">
<li class="Itemize-1 Itemize asterisk">
No seamless windows. All application windows are constrained to a
virtual desktop, which is displayed in a single window on the client
machine.
</li>
<li class="Itemize-1 Itemize asterisk">
TurboVNC generally requires about 20% more host CPU cycles to maintain
the same frame rate as the VGL Transport, both because it has to
compress more pixels in each frame (an entire desktop rather than a
single window) and because it has to perform 2D (X11) rendering as well
as 3D rendering.
</li>
<li class="Itemize-1 Itemize asterisk">
TurboVNC does not support quad-buffered stereo.
</li>
</ul>
<h2 id="hd009001">9.1 Using VirtualGL on a TurboVNC Host</h2>
<p>The most common (and optimal) way to use VirtualGL with TurboVNC is to
configure the same machine as a TurboVNC host and a VirtualGL server.
This allows VirtualGL to send rendered frames to TurboVNC through shared
memory rather than over a network.</p>
<div class="figure">
<img src="x11transport.png" alt="x11transport" class="figure" id="imgid_8" name="imgid_8"/>
</div>
<p>The following procedure describes how to launch a 3D application using
this configuration.</p>
<h3 id="hd009001001">Procedure</h3>
<ol class="Ordered numeric">
<li class="Ordered-1 Ordered">
Follow the procedure described in Chapter
<a href="#TurboVNC_Usage" class="ref">6</a> for starting a TurboVNC
session and connecting to it.
</li>
<li class="Ordered-1 Ordered">
Open a new terminal inside the remote desktop.
</li>
<li class="Ordered-1 Ordered">
In the terminal, start a 3D application using VirtualGL:
<pre class="verbatim">/opt/VirtualGL/bin/vglrun <em>[vglrun options]</em> <em>3D-application-executable-or-script</em> <em>[arguments]</em></pre>
</li>
</ol>
<h3 id="hd009001002">9.1.2 Running the Window Manager Using VirtualGL</h3>
<p><a name="VGLWM"></a></p>
<p>If the TurboVNC host is also a VirtualGL server, then you can pass
<code>-vgl</code> to <code>vncserver</code> or set the
<code>$useVGL</code> variable in
<strong class="filename">turbovncserver.conf</strong> to enable
VirtualGL for all OpenGL applications launched in the TurboVNC session,
including the window manager. This improves the performance of
compositing window managers and enables GPU acceleration for OpenGL
applications without the need to invoke <code>vglrun</code>.</p>
<div class="important"><p class="important">
To change VirtualGL’s configuration for a specific 3D application, start the application with <code>vglrun</code>, per above, or set one of the <code>VGL_*</code> configuration environment variables prior to starting the application. (Refer to the VirtualGL User’s Guide.)
</p></div>
<div class="important"><p class="important">
To disable VirtualGL for a specific 3D application, unset the <code>LD_PRELOAD</code> environment variable prior to starting the application.
</p></div>
<h2 id="hd009002">9.2 Using VirtualGL on a Machine Other Than a TurboVNC Host</h2>
<div class="figure">
<img src="vgltransportservernetwork.png" alt="vgltransportservernetwork" class="figure" id="imgid_9" name="imgid_9"/>
</div>
<p>If the TurboVNC host and VirtualGL server are different machines, then
it is desirable to use the VGL Transport to send rendered frames from
the VirtualGL server to the TurboVNC session. It is also desirable to
disable image compression in the VGL Transport. Otherwise, the images
would have to be compressed by the VirtualGL server, decompressed by the
VirtualGL Client, then recompressed by the TurboVNC Server, which is a
waste of CPU resources. However, sending images uncompressed over a
network requires a fast network (generally, Gigabit Ethernet or faster),
so there needs to be a fast link between the VirtualGL server and the
TurboVNC host for this procedure to perform well.</p>
<h3 id="hd009002001">Procedure</h3>
<ol class="Ordered numeric">
<li class="Ordered-1 Ordered">
Follow the procedure described in Chapter
<a href="#TurboVNC_Usage" class="ref">6</a> for starting a TurboVNC
session and connecting to it.
</li>
<li class="Ordered-1 Ordered">
Open a new terminal inside the remote desktop.
</li>
<li class="Ordered-1 Ordered">
In the same terminal window, open a Secure Shell (SSH) session into the
VirtualGL server:
<pre class="verbatim">/opt/VirtualGL/bin/vglconnect <em>[vglconnect options]</em> <em>user</em>@<em>server</em></pre>
Replace <em><code>user</code></em> with your username on the VirtualGL
server and <em><code>server</code></em> with the hostname or IP address
of that server. Refer to the VirtualGL User’s Guide for
additional <code>vglconnect</code> options.
</li>
<li class="Ordered-1 Ordered">
In the SSH session, set the <code>VGL_COMPRESS</code> environment
variable to <code>rgb</code>.
<div class="important"><p class="important">
Passing an argument of <code>-c rgb</code> to <code>vglrun</code> achieves the same result.
</p></div>
</li>
<li class="Ordered-1 Ordered">
In the SSH session, start a 3D application using VirtualGL:
<pre class="verbatim">/opt/VirtualGL/bin/vglrun <em>[vglrun options]</em> <em>3D-application-executable-or-script</em> <em>[arguments]</em></pre>
</li>
</ol>
<h2 id="hd009003">9.3 NV-CONTROL Emulation</h2>
<p>This version of TurboVNC includes partial emulation of the
<code>NV-CONTROL</code> X11 extension provided by nVidia’s
proprietary Un*x drivers. Certain 3D applications rely on this
extension to query and set low-level GPU properties, and unfortunately
the library (libXNVCtrl) used by applications to interact with the
extension is static, making it impossible to interpose using VirtualGL.</p>
<p>Passing an argument of <code>-nvcontrol <em>display</em></code> to
<code>vncserver</code> causes the TurboVNC Server to create a fake
<code>NV-CONTROL</code> extension in the TurboVNC session and redirect
all <code>NV-CONTROL</code> requests to <em><code>display</code></em>.
<em><code>display</code></em> should be the X display/screen of the 3D X
server you plan to use with VirtualGL (<code>:0.0</code>, for instance.)
The TurboVNC Server does not attempt to open a connection to this
display until an application uses the <code>NV-CONTROL</code> extension.
If a connection to the 3D X server cannot be opened, if the 3D X server
does not have the <code>NV-CONTROL</code> extension, or if other issues
are encountered when attempting to redirect <code>NV-CONTROL</code>
requests, then an X11 BadRequest error will be returned to the
application, and the TurboVNC session log will display an error message
explaining why the request failed. It is assumed that you have already
followed the procedure in the VirtualGL User’s Guide to allow
access to the 3D X server. If access to the 3D X server is restricted
to members of the <code>vglusers</code> group, then you may need to
execute</p>
<pre class="verbatim">
xauth merge /etc/opt/VirtualGL/vgl_xauth_key
</pre>
<p>in order to use the <code>NV-CONTROL</code> extension prior to invoking
<code>vglrun</code> for the first time.</p>
<p>You can change the 3D X server for a particular TurboVNC session after
the session has been started. For instance, if you wanted to redirect
both <code>NV-CONTROL</code> requests and OpenGL to a GPU attached to
Screen 1 of Display :0, then you could execute</p>
<pre class="verbatim">xprop -root -f VNC_NVCDISPLAY 8s -set VNC_NVCDISPLAY :0.1
vglrun -d :0.1 <em>3D-application-executable-or-script</em></pre>
<p><br /></p>
<hr class="break" />
<h1 id="hd0010"><a name="file010"></a>10 GPU-Accelerated OpenGL and Vulkan (Using the DRI3 X11 Extension)</h1>
<p><a name="DRI3"></a></p>
<p>The TurboVNC Server supports built-in GPU acceleration when using open
source (Mesa-based) GPU drivers. This is implemented through the
<code>DRI3</code> X11 extension, which can be enabled by passing
<code>-drinode <em>DRM-render-node</em></code> to <code>vncserver</code>
or adding the same command-line arguments to the value of the
<code>$serverArgs</code> variable in
<strong class="filename">turbovncserver.conf</strong> (or to the value
of the TurboVNC Viewer’s <code>ServerArgs</code> parameter, if
using the TurboVNC Session Manager.)
<em><code>DRM-render-node</code></em> is the DRM render node
corresponding to a GPU on the TurboVNC host (for example,
<code>/dev/dri/renderD128</code>.) Specifying a DRM render node of
<code>auto</code> is the equivalent of specifying the first DRM render
node under <strong class="filename">/dev/dri</strong>.</p>
<h3 id="hd0010000001">Advantages of DRI3 (when compared to <a href="#VGL">VirtualGL</a><a name="idx0041"></a>)</h3>
<ul class="Itemize">
<li class="Itemize-1 Itemize asterisk">
No additional software or setup required
</li>
<li class="Itemize-1 Itemize asterisk">
Supports GPU acceleration with Vulkan applications
</li>
</ul>
<h3 id="hd0010000002">Disadvantages of DRI3 (when compared to <a href="#VGL">VirtualGL</a><a name="idx0042"></a>)</h3>
<ul class="Itemize">
<li class="Itemize-1 Itemize asterisk">
Requires open source (Mesa-based) GPU drivers (does not work with
nVidia’s proprietary Un*x drivers)
</li>
<li class="Itemize-1 Itemize asterisk">
Generally has worse performance and more CPU overhead with OpenGL
applications
</li>
</ul>
<p>DRI3 is particularly useful with virtualization environments, such as
VMware and Parallels Desktop, that redirect 3D rendering from the guest
to the host. (The performance advantages of VirtualGL are less
pronounced in such environments.)</p>
<p>VirtualGL’s performance is generally affected very little or not
at all by the presence of the <code>DRI3</code> X11 extension, so using
DRI3 for Vulkan applications and VirtualGL for OpenGL applications is a
viable approach.</p>
<div class="important"><p class="important">
By default, Mesa-based GPU drivers synchronize 3D rendering to the vertical refresh rate (always 60 Hz in TurboVNC.) Set the <code>vblank_mode</code> environment variable to <code>1</code> to disable vertical refresh rate synchronization by default while allowing applications to override the default. Set the <code>vblank_mode</code> environment variable to <code>0</code> to force-disable vertical refresh rate synchronization.
</p></div>
<p><br /></p>
<hr class="break" />
<h1 id="hd0011"><a name="file011"></a>11 Compatibility Guide</h1>
<p><a name="Compatibility"></a></p>
<p>In order to realize the full benefits of TurboVNC, it is necessary to
use the TurboVNC Server and the TurboVNC Viewer together. However,
TurboVNC is compatible with TigerVNC, TightVNC, RealVNC, and other VNC
flavors. You can use the TurboVNC Viewer to connect to a non-TurboVNC
server (or vice versa), although this will generally result in some
decrease in performance, and features such as the
<a href="#TurboVNC_Session_Manager">TurboVNC Session
Manager</a><a name="idx0043"></a> will not be available.</p>
<p>The following sections list additional things to bear in mind when
mixing TurboVNC with other VNC flavors.</p>
<h2 id="hd0011001">11.1 TightVNC or TigerVNC Servers</h2>
<ul class="Itemize">
<li class="Itemize-1 Itemize asterisk">
TightVNC and TigerVNC specify the JPEG quality level on a scale from 0
to 9. This translates to actual JPEG quality as follows:
<dl class="Description">
<dt class="Description-3 Description">TightVNC JPEG Quality Levels</dt>
<dd class="Description-3 Description">
<div class="table">
<table class="standard">
<thead class="standard">
<tr class="head ">
<th class="head standard">JPEG quality level</th>
<th class="head standard">0</th>
<th class="head standard">1</th>
<th class="head standard">2</th>
<th class="head standard">3</th>
<th class="head standard">4</th>
<th class="head standard">5</th>
<th class="head standard">6</th>
<th class="head standard">7</th>
<th class="head standard">8</th>
<th class="head standard">9</th>
</tr>
</thead>
<tr class="standard">
<td class="high standard">Actual JPEG quality</td>
<td class="standard">5</td>
<td class="standard">10</td>
<td class="standard">15</td>
<td class="standard">25</td>
<td class="standard">37</td>
<td class="standard">50</td>
<td class="standard">60</td>
<td class="standard">70</td>
<td class="standard">75</td>
<td class="standard">80</td>
</tr>
<tr class="standard">
<td class="high standard">Actual chrominance subsampling</td>
<td class="standard">2X</td>
<td class="standard">2X</td>
<td class="standard">2X</td>
<td class="standard">2X</td>
<td class="standard">2X</td>
<td class="standard">2X</td>
<td class="standard">2X</td>
<td class="standard">2X</td>
<td class="standard">2X</td>
<td class="standard">2X</td>
</tr>
</table>
</div>
<a name="TigerVNC_JPEG_Qual"></a>
</dd>
<dt class="Description-3 Description">TigerVNC JPEG Quality Levels</dt>
<dd class="Description-3 Description">
<div class="table">
<table class="standard">
<thead class="standard">
<tr class="head ">
<th class="head standard">JPEG quality level</th>
<th class="head standard">0</th>
<th class="head standard">1</th>
<th class="head standard">2</th>
<th class="head standard">3</th>
<th class="head standard">4</th>
<th class="head standard">5</th>
<th class="head standard">6</th>
<th class="head standard">7</th>
<th class="head standard">8</th>
<th class="head standard">9</th>
</tr>
</thead>
<tr class="standard">
<td class="high standard">Actual JPEG quality</td>
<td class="standard">15</td>
<td class="standard">29</td>
<td class="standard">41</td>
<td class="standard">42</td>
<td class="standard">62</td>
<td class="standard">77</td>
<td class="standard">79</td>
<td class="standard">86</td>
<td class="standard">92</td>
<td class="standard">100</td>
</tr>
<tr class="standard">
<td class="high standard">Actual chrominance subsampling</td>
<td class="standard">4X</td>
<td class="standard">4X</td>
<td class="standard">4X</td>
<td class="standard">2X</td>
<td class="standard">2X</td>
<td class="standard">2X</td>
<td class="standard">1X</td>
<td class="standard">1X</td>
<td class="standard">1X</td>
<td class="standard">1X</td>
</tr>
<tr class="standard">
<td class="high standard">Average compression ratio *</td>
<td class="standard">100</td>
<td class="standard">80</td>
<td class="standard">70</td>
<td class="standard">60</td>
<td class="standard">50</td>
<td class="standard">40</td>
<td class="standard">30</td>
<td class="standard">25</td>
<td class="standard">20</td>
<td class="standard">10</td>
</tr>
</table>
</div>
<div class="important"><p class="important">
* Experimentally determined by compressing every 10th frame in the SPECviewperf 9 benchmark suite
</p></div>
</dd>
</dl>
TurboVNC, on the other hand, includes extensions to Tight encoding that
allow the JPEG quality to be specified on the standard 1-100 scale and
that allow the JPEG chrominance subsampling to be specified seperately.
TigerVNC 1.2 and later includes the same extensions on the server side,
so in this regard, the TigerVNC 1.2+ Server behaves like the TurboVNC
Server when a TurboVNC viewer is connected to it. <br /><br /> When a
TurboVNC viewer is connected to a TightVNC or TigerVNC 1.0/1.1 server,
setting the JPEG quality to N in the TurboVNC Viewer sets the JPEG
quality level to N/10 in the TightVNC or TigerVNC server. For instance,
if you set the JPEG quality to 95 in the TurboVNC Viewer, this would
translate to a JPEG quality level of 9, which would set the actual JPEG
quality/subsampling to 80/2X if connected to a TightVNC server and
100/1X if connected to a TigerVNC 1.0/1.1 server. <br /><br />
</li>
<li class="Itemize-1 Itemize asterisk">
Changing the JPEG chrominance subsampling option in the TurboVNC Viewer
has no effect when connected to a TightVNC or TigerVNC 1.0/1.1 server.
<br /><br />
</li>
<li class="Itemize-1 Itemize asterisk">
Normally, the TurboVNC Viewer Options dialog only allows you to select
the compression levels that are useful for the TurboVNC Server, but you
can use the TurboVNC Viewer’s <code>CompressLevel</code> parameter
to specify additional compression levels. You can also set the TurboVNC
Viewer’s <code>CompatibleGUI</code> parameter to expose all 10
compression levels in the TurboVNC Viewer Options dialog, which is
useful when connecting to non-TurboVNC servers. It should be noted,
however, that our experiments have shown that compression levels higher
than 5 are generally not useful in the TightVNC and TigerVNC Servers.
They increase CPU usage exponentially without significantly reducing
network usage relative to Compression Level 5. <br /><br />
</li>
<li class="Itemize-1 Itemize asterisk">
Zlib introduces a significant amount of performance overhead, even when
zlib compression level 0 (no compression) is used, so TurboVNC supports
a Tight encoding extension that allows the server to bypass zlib when
encoding a particular subrectangle. The extension is enabled when a VNC
viewer advertises support for it and requests Compression Level 0. As
of this writing, TightVNC and TigerVNC do not support the extension, so
the TightVNC and TigerVNC servers will use zlib to
“compress” framebuffer updates if you request Compression
Level 0 using the TurboVNC Viewer. <br /><br />
</li>
<li class="Itemize-1 Itemize asterisk">
When properly configured, version 1.2 and later (except versions 1.4.0 -
1.4.2, which contained a performance regression) of the TigerVNC Server
can be made to perform similarly to a single-threaded instance of the
TurboVNC Server. However, all other versions of TigerVNC and TightVNC
will use much more CPU time across the board than the TurboVNC Server,
all else being equal. With JPEG enabled, Compression Levels 1 and 2 in
TigerVNC are roughly equivalent to the same compression levels in
TurboVNC, except that TigerVNC enables interframe comparison
automatically with Compression Level 2 and above.
</li>
</ul>
<h2 id="hd0011002">11.2 TightVNC or TigerVNC Viewers</h2>
<ul class="Itemize">
<li class="Itemize-1 Itemize asterisk">
When either a TightVNC or TigerVNC viewer is connected to a TurboVNC
session, the TurboVNC Server emulates the behavior of a TigerVNC server,
translating JPEG quality levels into actual JPEG quality and subsampling
as specified in Section
<a href="#TigerVNC_JPEG_Qual" class="ref">11.1</a>. <br /><br />
</li>
<li class="Itemize-1 Itemize asterisk">
Zlib introduces a significant amount of performance overhead, even when
zlib compression level 0 (no compression) is used, so TurboVNC supports
a Tight encoding extension that allows the server to bypass zlib when
encoding a particular subrectangle. The extension is enabled when a VNC
viewer advertises support for it and requests Compression Level 0. As
of this writing, TightVNC and TigerVNC do not support the extension, so
the TurboVNC Server will use zlib to “compress” framebuffer
updates if you request Compression Level 0 using the TightVNC or
TigerVNC Viewer. <br /><br />
</li>
<li class="Itemize-1 Itemize asterisk">
Refer to Section <a href="#AdvancedCompression" class="ref">7.2</a> for
a description of how the TurboVNC Server implements Compression Levels
0-9. <br /><br />
</li>
</ul>
<h2 id="hd0011003">11.3 RealVNC</h2>
<p>The TurboVNC Viewer supports the Hextile, Raw, and ZRLE encoding types,
which are compatible with RealVNC. None of those encoding types can be
selected from the TurboVNC Viewer Options dialog, but Hextile or ZRLE
will be selected automatically when connecting to a RealVNC server.
Non-Tight encoding types, such as Hextile and Raw, can also be specified
using the TurboVNC Viewer’s <code>Encoding</code> parameter. In
addition to Hextile, Raw, and ZRLE, the TurboVNC Server also supports
the RRE, CoRRE, and Zlib legacy encoding types, for compatibility with
older VNC viewers.</p>
<p>All of the non-Tight encoding types have performance drawbacks. Raw
encoding requires a gigabit or faster network in order to achieve decent
performance, and it can easily take up all of the bandwidth on a gigabit
network. (It also doesn’t perform particularly well in the
TurboVNC Viewer, because of the need to convert pixels from bytes to
ints in Java.) Hextile uses very small tiles, which causes it to incur
a large amount of computational overhead. It compresses too poorly to
perform well on slow networks but uses too much CPU time to perform well
on fast networks. ZRLE improves upon this, but it is still too
computationally intense for fast networks. The <code>vncviewer</code>
man page contains additional information about how Hextile and ZRLE work.</p>
<p><br /></p>
<hr class="break" />
<h1 id="hd0012"><a name="file012"></a>12 Advanced Configuration</h1>
<h2 id="hd0012001">12.1 Server Settings</h2>
<p>The TurboVNC Server is normally configured in the following ways, in
increasing order of precedence:</p>
<ol class="Ordered numeric">
<li class="Ordered-1 Ordered">
A system-wide configuration file
(<strong class="filename">/etc/turbovncserver.conf</strong>), which can
be used to modify the default values of certain <code>vncserver</code>
and <code>Xvnc</code> command-line options
</li>
<li class="Ordered-1 Ordered">
A per-user configuration file
(<strong class="filename">~/.vnc/turbovncserver.conf</strong>), which
can be used to modify the default values of certain
<code>vncserver</code> and <code>Xvnc</code> command-line options
</li>
<li class="Ordered-1 Ordered">
<code>vncserver</code> and <code>Xvnc</code> command-line options
</li>
<li class="Ordered-1 Ordered">
<code>tvncconfig</code>, which can be used to modify certain TurboVNC
Server parameters in a running TurboVNC session
</li>
<li class="Ordered-1 Ordered">
A system-wide security configuration file
(<strong class="filename">/etc/turbovncserver-security.conf</strong>),
which can be used to configure certain TurboVNC Server security features
as well as restrict the scope of TurboVNC Server features that users are
allowed to configure
</li>
</ol>
<p>Refer to the TurboVNC man pages for more information:</p>
<pre class="verbatim">
man -M /opt/TurboVNC/man vncserver
man -M /opt/TurboVNC/man Xvnc
man -M /opt/TurboVNC/man vncconnect
man -M /opt/TurboVNC/man vncpasswd
man -M /opt/TurboVNC/man tvncconfig
</pre>
<p><br /> This section documents rarely-used advanced TurboVNC Server
settings that can be configured using environment variables.</p>
<div class="table">
<table class="standard">
<tr class="standard">
<td class="high standard">Environment Variable</td>
<td class="standard"><code>TVNC_ALRALL = <em>0 | 1</em></code></td>
</tr>
<tr class="standard">
<td class="high standard">TurboVNC Server Parameter</td>
<td class="standard"><code>ALRAll = <em>False | True</em></code></td>
</tr>
<tr class="standard">
<td class="high standard">Summary</td>
<td class="standard">Disable/Enable automatic lossless refresh for regions that were drawn using X11 functions other than <code>X[Shm]PutImage()</code></td>
</tr>
<tr class="standard">
<td class="high standard">Default Value</td>
<td class="standard">Disabled</td>
</tr>
</table>
</div>
<dl class="Description">
<dt class="Description-1 Description">Description</dt>
<dd class="Description-1 Description">
See Section <a href="#ALR" class="ref">7.4</a>
</dd>
</dl>
<div class="table">
<table class="standard">
<tr class="standard">
<td class="high standard">Environment Variable</td>
<td class="standard"><code>TVNC_ALRCOPYRECT = <em>0 | 1</em></code></td>
</tr>
<tr class="standard">
<td class="high standard">Summary</td>
<td class="standard">Disable/Enable automatic lossless refresh for regions that were drawn using CopyRect</td>
</tr>
<tr class="standard">
<td class="high standard">Default Value</td>
<td class="standard">Enabled</td>
</tr>
</table>
</div>
<dl class="Description">
<dt class="Description-1 Description">Description</dt>
<dd class="Description-1 Description">
See Section <a href="#ALR" class="ref">7.4</a>
</dd>
</dl>
<div class="table">
<table class="standard">
<tr class="standard">
<td class="high standard">Environment Variable</td>
<td class="standard"><code>TVNC_COMBINERECT = <em>{c}</em></code></td>
</tr>
<tr class="standard">
<td class="high standard">Summary</td>
<td class="standard">Combine framebuffer updates with more than <em><code>{c}</code></em> rectangles into a single rectangle spanning the bounding box of all of the constituent rectangles</td>
</tr>
<tr class="standard">
<td class="high standard">Default Value</td>
<td class="standard"><code>100</code></td>
</tr>
</table>
</div>
<dl class="Description">
<dt class="Description-1 Description">Description</dt>
<dd class="Description-1 Description">
Applications can sometimes draw many thousands of points or tiny lines
using individual X11 calls, and this can cause the VNC server to send
many thousands of tiny rectangles to the VNC viewer. The overhead
associated with this can bog down the viewer, and in extreme cases, the
number of rectangles may even exceed the maximum number that is allowed
in a single framebuffer update (65534.) Thus, if a framebuffer update
contains more than <em><code>{c}</code></em> rectangles, the TurboVNC
Server will coalesce it into a single rectangle that covers all of the
rectangles in the update. For applications that generate many tiny
rectangles, increasing the value of <code>TVNC_COMBINERECT</code> may
significantly increase the number of pixels sent to the viewer, which
will increase network usage. However, for those same applications,
lowering the value of <code>TVNC_COMBINERECT</code> will increase the
number of rectangles sent to the viewer, which will increase the CPU
usage of both the server and the viewer.
</dd>
</dl>
<div class="table">
<table class="standard">
<tr class="standard">
<td class="high standard">Environment Variable</td>
<td class="standard"><code>TVNC_ICEBLOCKSIZE = <em>{s}</em></code></td>
</tr>
<tr class="standard">
<td class="high standard">Summary</td>
<td class="standard">Set the block size for the interframe comparison engine (ICE) to <em><code>{s}</code></em> x <em><code>{s}</code></em> pixels. Setting <em><code>{s}</code></em> to 0 causes the ICE to compare full rectangles, as TurboVNC 1.2.x did.</td>
</tr>
<tr class="standard">
<td class="high standard">Default Value</td>
<td class="standard"><code>256</code></td>
</tr>
</table>
</div>
<dl class="Description">
<dt class="Description-1 Description">Description</dt>
<dd class="Description-1 Description">
If interframe comparison is enabled (see Section
<a href="#InterframeComparison" class="ref">7.1</a>), then the TurboVNC
Server compares each rectangle of each framebuffer update on a
block-by-block basis and sends only the blocks that have changed. This
prevents large rectangles from being re-transmitted if only a few pixels
in the rectangle have changed. Using smaller block sizes can decrease
network usage if only a few pixels have changed between updates.
However, using smaller block sizes can also interfere with the Tight
encoder’s ability to efficiently split rectangles into
subrectangles, thus increasing host CPU usage (and sometimes increasing
network usage as well, which defeats the purpose of interframe
comparison.) Setting the block size to 0 causes the ICE to compare full
framebuffer update rectangles, as TurboVNC 1.2.x did. <br /><br /> The
default block size of 256x256 was chosen based on extensive low-level
experiments using the same set of RFB session captures that were used
when designing the TurboVNC encoder. For most of those datasets,
256x256 blocks produced the lowest network and CPU usage, but actual
mileage may vary. There were rare cases in which 64x64 blocks or
full-rectangle comparison produced better network and CPU usage.
</dd>
</dl>
<div class="table">
<table class="standard">
<tr class="standard">
<td class="high standard">Environment Variable</td>
<td class="standard"><code>TVNC_ICEDEBUG = <em>0 | 1</em></code></td>
</tr>
<tr class="standard">
<td class="high standard">Summary</td>
<td class="standard">Disable/Enable the ICE debugger</td>
</tr>
<tr class="standard">
<td class="high standard">Default Value</td>
<td class="standard">Disabled</td>
</tr>
</table>
</div>
<dl class="Description">
<dt class="Description-1 Description">Description</dt>
<dd class="Description-1 Description">
If interframe comparison is enabled (see Section
<a href="#InterframeComparison" class="ref">7.1</a>), then setting this
environment variable to <code>1</code> will cause the interframe
comparison engine (ICE) to change the color of duplicate screen regions
without culling them from the framebuffer update stream. This allows
you to easily see which applications are generating duplicate updates.
</dd>
</dl>
<div class="table">
<table class="standard">
<tr class="standard">
<td class="high standard">Environment Variable</td>
<td class="standard"><code>TVNC_MT = <em>0 | 1</em></code></td>
</tr>
<tr class="standard">
<td class="high standard">Summary</td>
<td class="standard">Disable/Enable multithreaded image encoding</td>
</tr>
<tr class="standard">
<td class="high standard">Default Value</td>
<td class="standard">Enabled</td>
</tr>
</table>
</div>
<dl class="Description">
<dt class="Description-1 Description">Description</dt>
<dd class="Description-1 Description">
See Section <a href="#Multithreading" class="ref">7.5</a>
</dd>
</dl>
<div class="table">
<table class="standard">
<tr class="standard">
<td class="high standard">Environment Variable</td>
<td class="standard"><code>TVNC_NTHREADS = <em>{n}</em></code></td>
</tr>
<tr class="standard">
<td class="high standard">Summary</td>
<td class="standard">Use <em><code>{n}</code></em> threads (1 <= <em><code>{n}</code></em> <= 4) to perform image encoding</td>
</tr>
<tr class="standard">
<td class="high standard">Default Value</td>
<td class="standard"><em><code>{n}</code></em> = the number of CPU cores in the system, up to a maximum of 4</td>
</tr>
</table>
</div>
<dl class="Description">
<dt class="Description-1 Description">Description</dt>
<dd class="Description-1 Description">
See Section <a href="#Multithreading" class="ref">7.5</a>
</dd>
</dl>
<div class="table">
<table class="standard">
<tr class="standard">
<td class="high standard">Environment Variable</td>
<td class="standard"><code>TVNC_PROFILE = <em>0 | 1</em></code></td>
</tr>
<tr class="standard">
<td class="high standard">TurboVNC Server Parameter</td>
<td class="standard"><code>Profile = <em>False | True</em></code></td>
</tr>
<tr class="standard">
<td class="high standard">Summary</td>
<td class="standard">Disable/enable profiling output</td>
</tr>
<tr class="standard">
<td class="high standard">Default Value</td>
<td class="standard">Disabled</td>
</tr>
</table>
</div>
<dl class="Description">
<dt class="Description-1 Description">Description</dt>
<dd class="Description-1 Description">
If profiling output is enabled, then the TurboVNC Server will
continuously benchmark itself and periodically print the throughput of
various stages in its image pipeline to the TurboVNC session log.
</dd>
</dl>
<h2 id="hd0012002">12.2 Viewer Settings</h2>
<p>The TurboVNC Viewer is normally configured in the following ways, in
increasing order of precedence:</p>
<ol class="Ordered numeric">
<li class="Ordered-1 Ordered">
A per-user configuration file
(<strong class="filename">~/.vnc/default.turbovnc</strong>), which can
be used to modify the default values of TurboVNC Viewer parameters
</li>
<li class="Ordered-1 Ordered">
TurboVNC Viewer parameters, which can be set on the command line or in a
connection info file
</li>
</ol>
<p>Run</p>
<pre class="verbatim">
/opt/TurboVNC/bin/vncviewer -?
</pre>
<p>on Linux/Un*x and Mac systems or</p>
<pre class="verbatim">
c:\Program Files\TurboVNC\vncviewer.bat -?
</pre>
<p>on Windows systems to display a list of command-line options and
commonly-used parameters and their descriptions. Replace
<code>-?</code> with <code>-??</code> to display a list of advanced
parameters and their descriptions.</p>
<p><br /> This section documents rarely-used advanced TurboVNC Viewer
settings that can be configured using environment variables or Java
system properties.</p>
<p>Java system properties can be set using the
<code>JAVA_TOOL_OPTIONS</code> environment variable. For instance, on
Linux/Un*x and Mac systems, you could execute:</p>
<pre class="verbatim">
JAVA_TOOL_OPTIONS=-Dturbovnc.sessmgr=0 /opt/TurboVNC/bin/vncviewer
</pre>
<p>to start the TurboVNC Viewer with the TurboVNC Session Manager disabled.
The Java system properties listed below can also be specified in
<strong class="filename">~/.vnc/default.turbovnc</strong>.</p>
<div class="table">
<table class="standard">
<tr class="standard">
<td class="high standard">Java System Property</td>
<td class="standard"><code>turbovnc.fshidedock = <em>0 | 1</em></code></td>
</tr>
<tr class="standard">
<td class="high standard">Summary</td>
<td class="standard">Always show/always hide the menu bar and dock in full-screen mode</td>
</tr>
<tr class="standard">
<td class="high standard">Platforms</td>
<td class="standard">Mac</td>
</tr>
<tr class="standard">
<td class="high standard">Default Value</td>
<td class="standard">Hide the menu bar and dock in full-screen mode if bump scrolling is enabled</td>
</tr>
</table>
</div>
<dl class="Description">
<dt class="Description-1 Description">Description</dt>
<dd class="Description-1 Description">
By default, the Mac TurboVNC Viewer hides the menu bar and dock in
full-screen mode if bump scrolling is enabled. Setting this property to
<code>0</code> or <code>1</code> causes the viewer to always show or
always hide the menu bar and dock in full-screen mode, irrespective of
bump scrolling.
</dd>
</dl>
<div class="table">
<table class="standard">
<tr class="standard">
<td class="high standard">Java System Property</td>
<td class="standard"><code>turbovnc.primary = <em>0 | 1</em></code></td>
</tr>
<tr class="standard">
<td class="high standard">Summary</td>
<td class="standard">Disable/enable the use of the X11 PRIMARY clipboard selection</td>
</tr>
<tr class="standard">
<td class="high standard">Default Value</td>
<td class="standard">Enabled</td>
</tr>
</table>
</div>
<dl class="Description">
<dt class="Description-1 Description">Description</dt>
<dd class="Description-1 Description">
X11 has two ways of copying/pasting text. When text is selected in most
X11 applications, it is copied to the PRIMARY selection, and it can be
pasted by pressing the middle mouse button. When text is explicitly
copied using a “Copy” menu option or a hotkey (such as
CTRL-C), it is copied to the CLIPBOARD selection, and it can only be
pasted using a “Paste” menu option or a hotkey (such as
CTRL-V.) Normally, on X11 platforms, the TurboVNC Viewer transfers the
PRIMARY selection from client to server, and when receiving a clipboard
update from the server, it sets both the PRIMARY and CLIPBOARD
selections with the server’s clipboard contents. Disabling this
property causes only the CLIPBOARD selection to be transferred from
client to server. (In other words, the clipboard will not be
transferred unless you explicitly copy something using a menu option or
a hotkey.) Also, if this property is disabled, then clipboard changes
from the server will only affect the client’s CLIPBOARD selection.
(In other words, you will have to use a menu option or a hotkey to paste
the server’s clipboard contents.)
</dd>
</dl>
<div class="table">
<table class="standard">
<tr class="standard">
<td class="high standard">Java System Property</td>
<td class="standard"><code>turbovnc.sessmgr = <em>0 | 1</em></code></td>
</tr>
<tr class="standard">
<td class="high standard">Summary</td>
<td class="standard">Disable/enable the TurboVNC Session Manager</td>
</tr>
<tr class="standard">
<td class="high standard">Default Value</td>
<td class="standard">Enabled</td>
</tr>
</table>
</div>
<dl class="Description">
<dt class="Description-1 Description">Description</dt>
<dd class="Description-1 Description">
Disabling this property will completely disable the TurboVNC Session
Manager.
</dd>
</dl>
<div class="table">
<table class="standard">
<tr class="standard">
<td class="high standard">Environment Variable</td>
<td class="standard"><code>TVNC_SINGLESCREEN = <em>0 | 1</em></code></td>
</tr>
<tr class="standard">
<td class="high standard">Java System Property</td>
<td class="standard"><code>turbovnc.singlescreen = <em>0 | 1</em></code></td>
</tr>
<tr class="standard">
<td class="high standard">Summary</td>
<td class="standard">Disable/enable forcing a single-screen layout when using automatic desktop resizing</td>
</tr>
<tr class="standard">
<td class="high standard">Default Value</td>
<td class="standard">Disabled</td>
</tr>
</table>
</div>
<dl class="Description">
<dt class="Description-1 Description">Description</dt>
<dd class="Description-1 Description">
If automatic desktop resizing and multi-screen spanning are enabled,
then the TurboVNC Viewer normally requests a screen layout from the
server that fits within the viewer window without using scrollbars and
that aligns the server’s screen boundaries with the client’s
when the viewer window is in its default position. Setting this
environment variable or property to <code>1</code> restores the
automatic desktop resizing behavior of version 2.1.x and prior of the
TurboVNC Viewer, requesting a single-screen layout from the server even
if it supports multi-screen layouts.
</dd>
</dl>
<div class="table">
<table class="standard">
<tr class="standard">
<td class="high standard">Java System Property</td>
<td class="standard"><code>turbovnc.sshbannerdlg = <em>0 | 1</em></code></td>
</tr>
<tr class="standard">
<td class="high standard">Summary</td>
<td class="standard">Display the banner message from the SSH server in a dialog box</td>
</tr>
<tr class="standard">
<td class="high standard">Default Value</td>
<td class="standard">Disabled</td>
</tr>
</table>
</div>
<dl class="Description">
<dt class="Description-1 Description">Description</dt>
<dd class="Description-1 Description">
The default behavior of the TurboVNC Viewer is to display the banner
message from the SSH server on the command line. Enabling this property
causes the viewer to display the banner message in a dialog box instead.
</dd>
</dl>
<p><br /></p>
</body>
</html>