User’s Guide for TurboVNC 1.2.2
This document and all associated illustrations are licensed under the Creative Commons Attribution 2.5 License. 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.
The official TurboVNC binaries contain libjpeg-turbo, which is based in part on the work of the Independent JPEG Group.
The TurboVNC Windows packages include PuTTY, which is released under this license.
TurboVNC is licensed under the GNU General Public License, v2.
This document assumes that TurboVNC will be installed in the default
directory (/opt/TurboVNC
on Linux/Un*x and Mac systems and
c:\Program Files\TurboVNC
on Windows systems.) If
your installation of TurboVNC resides in a different directory, then
adjust the instructions accordingly.
TurboVNC is a derivative of VNC (Virtual Network Computing) that is tuned to provide peak performance for 3D and video workloads. TurboVNC was originally based on the TightVNC 1.3.x and xf4vnc code bases, and on the surface, it behaves similarly to its parents. However, 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 7.2.)
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.
Part of TurboVNC’s speedup comes from the use of libjpeg-turbo, the same high-speed SIMD-optimized JPEG codec used by VirtualGL. 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.
TurboVNC is the product of extensive research, in which many different permutations of the TightVNC encoder were benchmarked at the low level against a variety of captured RFB sessions that simulate real-world application workloads, both 2D and 3D. For more information on the research leading to TurboVNC’s encoder design, see this report.
In addition to high performance, other notable features of TurboVNC include:
TurboVNC, when used with VirtualGL, provides a highly performant and robust solution for remotely displaying 3D applications over all types of networks.
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.
TurboVNC is compatible with other VNC distributions. See Chapter 10 for more information. The official TurboVNC binaries can be installed onto the same system as other VNC distributions without interference.
Server (x86) | Server (x86-64) | Client | |
---|---|---|---|
Recommended CPU |
|
Dual processors or dual cores recommended | For optimal performance, the CPU should support SSE2 extensions. |
O/S | TurboVNC should work with a variety of Linux distributions, FreeBSD, and Solaris, but currently-supported versions of Red Hat Enterprise Linux (and its work-alikes, including CentOS, Oracle Linux, and Scientific Linux), Ubuntu LTS, and SuSE Linux Enterprise tend to receive the most attention from the TurboVNC community. | ||
Other | For optimal performance, the X server should be configured to export True Color (24-bit or 32-bit) visuals. |
Client | |
---|---|
Recommended CPU | Any Intel-based Mac |
O/S | OS X 10.5 (“Leopard”) or later |
Other Software | Java 1.5 or later (Java 1.6 or later recommended) |
Client | |
---|---|
Recommended CPU | For optimal performance, the CPU should support SSE2 extensions. |
O/S | Windows 2000 SP1 or later |
Other | For optimal performance, the client display should have a 24-bit or 32-bit (True Color) color depth. |
On some Linux distributions, most notably Fedora 10 and later, the basic
X11 bitmap fonts are not installed by default. Thus, it is necessary to
install the xorg-x11-fonts-misc
package on these
distributions prior to starting a TurboVNC session for the first time.
Otherwise, TurboVNC will fail with the following error:
Fatal server error: could not open default font 'fixed'
rpm -U turbovnc*.rpm
dpkg -i turbovnc*.deb
TurboVNC-
{version}
.dmg
)
from the
Files
area of the
TurboVNC
SourceForge project page.
TurboVNC.pkg
inside the disk
image. Follow the instructions to install the Mac TurboVNC Viewer.
TurboVNC-
{version}
.exe
for 32-bit systems or
TurboVNC64-
{version}
.exe
for 64-bit systems) from the
Files
area of the
TurboVNC
SourceForge project page.
If you are using a Linux/Un*x platform for which there is not a
pre-built TurboVNC binary package available, then log in as root,
download the TurboVNC source tarball
(turbovnc-
{version}
.tar.gz
)
from the
Files
area of the
TurboVNC
SourceForge project page, uncompress
it, cd turbovnc-
{version}
, and
read BUILDING.txt
for further instructions on how to build
TurboVNC from source.
As root, issue one of the following commands:
rpm -e turbovnc
dpkg -r turbovnc
Open the “Uninstall TurboVNC” application, located in the “TurboVNC” Applications folder. You can also open a terminal and execute:
sudo /opt/TurboVNC/bin/uninstall
Use the “Programs and Features” applet in the Control Panel (or the “Add or Remove Programs” applet if you are running Windows XP), or select “Uninstall TurboVNC” in the “TurboVNC” Start Menu group.
ssh {user}@{server}
"c:\program files\turbovnc\putty" {user}@{server}Replace
{user}
with your username on the TurboVNC
server machine and {server}
with the hostname or
IP address of that machine.
/opt/TurboVNC/bin/vncserver
Desktop 'TurboVNC: my_server:1 (my_user)' started on display my_server:1
/opt/TurboVNC/bin/vncviewer
Windows TurboVNC Viewer | X11 TurboVNC Viewer | Mac/Java TurboVNC Viewer |
---|---|---|
Windows TurboVNC Viewer | X11 TurboVNC Viewer | Mac/Java TurboVNC Viewer | |
---|---|---|---|
Standard VNC Authentication Dialog | |||
Unix Login Authentication Dialog |
Closing the TurboVNC Viewer disconnects from the TurboVNC session, but the TurboVNC session will remain running on the TurboVNC server machine (as will any applications that you may have started within the session), and you can reconnect to the session at any time.
To kill a TurboVNC session:
c:\Program Files\TurboVNC\putty.exe
on
Windows clients), log into the server machine that is running the
TurboVNC session you want to kill./opt/TurboVNC/bin/vncserver -kill :{n}Replace
{n}
with the X display number of the
TurboVNC session you want to kill.
To list the X display numbers and process ID’s of all TurboVNC sessions currently running under your user account on a particular server machine, type the following command:
/opt/TurboVNC/bin/vncserver -list
When a TurboVNC session is created, it automatically launches a miniature web server that serves up the Java TurboVNC Viewer as an applet. The Java TurboVNC Viewer can be used to connect to the TurboVNC session from a machine that does not have a native TurboVNC viewer installed (or a machine for which no native TurboVNC viewer is available.) The Java TurboVNC Viewer, when run as an applet, is significantly slower than the native viewer on high-speed networks, but on low-speed networks, the Java applet and native viewers have comparable performance.
To use the Java TurboVNC Viewer in a web browser, point your web browser to:
http://
{turbovnc_server}
:{5800+
n
}
where {turbovnc_server}
is the hostname or IP
address of the TurboVNC server machine, and n
is
the X display number of the TurboVNC session to which you want to
connect.
Example: If the TurboVNC session is occupying X display
my_server:1
, then point your web browser to:
http://my_server:5801
Normally, the connection between the TurboVNC Server and the TurboVNC Viewer is completely unencrypted, but securing that connection can be easily accomplished by using the port forwarding feature of Secure Shell (SSH.) After you have started a TurboVNC session on the TurboVNC server machine, open a new SSH connection into the TurboVNC server machine using the following command line:
ssh -L {5900+n}:localhost:{5900+n} {user}@{server}
"c:\program files\turbovnc\putty" -L {5900+n}:localhost:{5900+n} {user}@{server}
Replace {user}
with your username on the TurboVNC
server machine and {server}
with the hostname or
IP address of that machine. Replace n
with the X
display number of the TurboVNC session to which you want to connect.
For instance, if you want to connect to display :1
on
server my_server
using user account my_user
,
you would type:
ssh -L 5901:localhost:5901 my_user@my_server
"c:\program files\turbovnc\putty" -L 5901:localhost:5901 my_user@my_server
After the SSH connection has been established, you can then launch the
TurboVNC Viewer and point it to
localhost:
{n}
(localhost:1
in the above example.)
You can force PuTTY to use an IPv6 interface for the local end of the tunnel by replacing -L
with -L6
in the above command line.
-via
and -tunnel
Command-Line OptionsIf you are using the X11 and Java/Mac TurboVNC Viewers, then you can
simplify the above by using the -via
and
-tunnel
command-line options. For instance, running
{vncviewer} -via {user}@{server} localhost:{n}
or
{vncviewer} -tunnel {user}@{server}
is the equivalent of running
/usr/bin/ssh -L {fp}:localhost:{5900+n} {user}@{server} {vncviewer} localhost::{fp}
where {fp}
is a free TCP port on the client
machine (this is automatically determined by the TurboVNC Viewer.)
In the above examples, {vncviewer}
is the command used to launch the TurboVNC Viewer– /opt/TurboVNC/bin/vncviewer
if running the X11 or Mac TurboVNC Viewer, /opt/TurboVNC/bin/vncviewer-java
if running the Java TurboVNC Viewer on Linux/Un*x systems, or c:\Program Files\TurboVNC\vncviewer-java.bat
if running the Java TurboVNC Viewer on Windows systems.
-tunnel
can be used as a shortcut whenever the SSH and VNC
servers are the same machine. -via
is more flexible, since
it allows you to specify the VNC server to which to connect. The VNC
server is specified from the point of view of the SSH server, which is
why we used localhost
in the above example.
With the X11 TurboVNC Viewer, the command used to establish the SSH
tunnel is configurable by way of environment variables. See the
vncviewer
man page for more details.
NOTE: Since the Java TurboVNC Viewer contains an embedded SSH client, the -via
and -tunnel
parameters can also be used when the viewer is run as an applet or deployed using Java Web Start.
Passing an argument of -localhost
to vncserver
will force the TurboVNC Server session to accept inbound connections
only from the server machine. This effectively forces SSH tunneling to
be used for remote connections. If the
no-remote-connections
directive is set in the TurboVNC
authentication configuration file, then that has the effect of enabling
the -localhost
option for all new TurboVNC sessions that
are started on the machine.
Passing an argument of -noreverse
to vncserver
will disable the ability to make outbound (reverse) connections from the
TurboVNC Server session. If the no-reverse-connections
directive is set in the TurboVNC authentication configuration file, then
that has the effect of enabling the -noreverse
option for
all new TurboVNC sessions that are started on the machine.
For LAN connections and other high-speed networks, tunneling the TurboVNC connection through SSH will reduce performance by as much as 20-40%. For wide-area networks, however, there is no performance penalty for using SSH tunneling with TurboVNC.
For more detailed instructions on the usage of TurboVNC:
man -M /opt/TurboVNC/man vncserver man -M /opt/TurboVNC/man Xvnc man -M /opt/TurboVNC/man vncconnect man -M /opt/TurboVNC/man vncpasswd
vncviewer
man page:
man -M /opt/TurboVNC/man vncviewer
vncviewer.exe /?
from a command prompt to get a full
list of supported command-line options and their descriptions.
{vncviewer} -?to display a full list of supported command-line options/parameters and their descriptions, where
{vncviewer}
is the command used
to launch the Java TurboVNC Viewer–
/opt/TurboVNC/bin/vncviewer
on Mac platforms,
/opt/TurboVNC/bin/vncviewer-java
on Linux/Un*x platforms,
or c:\Program Files\TurboVNC\vncviewer-java.bat
on
Windows platforms.
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:
In the Windows and Java/Mac TurboVNC Viewers, these parameters can be adjusted by accessing the TurboVNC Viewer Options dialog box (click on the “Options” button in the “TurboVNC Connection” dialog box or, after connecting to the server, click on the Connection Options button in the toolbar.) In the X11 TurboVNC Viewer, press F8 after connecting to bring up the TurboVNC Viewer Options menu.
The TurboVNC Viewer provides five preset “encoding methods”, corresponding to the most useful combinations of the image compression options described above:
Encoding method | Allow JPEG | JPEG image quality | JPEG chrominance subsampling | Zlib compression level | Notes |
---|---|---|---|---|---|
“Tight + Perceptually Lossless JPEG” | Yes | 95 | 1x | 1 | 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. |
“Tight + Medium-Quality JPEG” | Yes | 80 | 2x | 1 | 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. |
“Tight + Low-Quality JPEG” | Yes | 30 | 4x | 1 | 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 Lossless Refresh feature. |
“Lossless Tight” | No | N/A | N/A | None | This encoding method uses indexed color subencoding for subrectangles that have a low number of unique colors, but it otherwise does not perform any image compression at all. Lossless Tight is thus suitable only for gigabit and faster networks. This encoding method uses significantly less CPU time than any of the JPEG-based encoding methods. Lossless Tight requires an RFB protocol extension that is, as of this writing, only supported by the TurboVNC Viewer. |
“Lossless Tight + Zlib” | No | N/A | N/A | 1 | 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. |
In the Windows and Java/Mac TurboVNC Viewers, the encoding method can be set in the TurboVNC Viewer Options dialog box (click on the “Options” button in the “TurboVNC Connection” dialog box or, after connecting to the server, click on the Connection Options button in the toolbar.)
With the X11 TurboVNC Viewer, the “Perceptually Lossless” encoding method is the default (unless it has been overridden using a resource file), but the following command-line switches can be used to specify the encoding method:
-highqual
= select the “Tight + Perceptually Lossless
Quality JPEG” encoding method
-medqual
=
select the “Tight + Medium-Quality JPEG” encoding method
-lowqual
= select the “Tight + Low-Quality
JPEG” encoding method
-lossless
= select the
“Lossless Tight” encoding method
-losslesswan
= select the “Lossless Tight +
Zlib” encoding method
After connecting, you can also press the F8 key to pop up the TurboVNC Viewer Options menu, from which you can select a different encoding method.
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. 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 rectangles before they are sent to the viewer.
Interframe comparison has some tradeoffs associated with it. 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 clients. 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 server CPU usage (since fewer rectangles are actually being encoded.) However, with 3D applications, interframe comparison increases server CPU usage without providing any significant reduction in network usage. Furthermore, the effects of duplicate framebuffer updates are not typically noticeable on high-speed networks, but an increase in server CPU usage might be.
For these reasons, interframe comparison is not enabled by default and
should not generally be enabled except on low-bandwidth networks and
with applications for which it can be shown to be beneficial.
Interframe comparison can be enabled by either passing an argument of
-interframe
to vncserver
when starting a
TurboVNC Server session or by requesting a compression level of 5 or
higher from the viewer (see below.)
One of the underlying principles of TurboVNC’s design is to expose only the options that provide the best performance “bang for the buck.” Thus, the TurboVNC Viewer GUI does not normally provide any way of requesting a compression level greater than 1. Compression Levels 2-9 can, however, be specified on the command line (or as a parameter, if using the Java TurboVNC Viewer), and doing so will enable an advanced mode in the TurboVNC Viewer GUI that allows any compression level from 0 to 9 to be requested.
When connecting to a TurboVNC server, requesting a particular compression level has the following effect:
Compression level | Zlib compression level (non-JPEG subrectangles) | Palette threshold | Interframe comparison | Notes |
---|---|---|---|---|
0 | 1 | 24 | No | 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. Further, bypassing zlib requires an RFB protocol extension that is not supported by non-TurboVNC viewers. 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. |
1 | 1 | 24 | No | See the description of the “Tight + JPEG” encoding methods above. |
2 | 3 | 96 | No | 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. |
3-4 | 3 | 96 | No | Same as Compression Level 2 (reserved for future expansion) |
5-6 | 1 | 24 | Yes | Same as Compression Level 1, but with interframe comparison enabled |
7-8 | 3 | 96 | Yes | Same as Compression Level 2, but with interframe comparison enabled |
9 | 7 | 256 | Yes | 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 apps (and has no noticeable benefit for 3D and video apps.) Thus, its usefulness is generally very limited. |
Compression Level | Zlib compression level (indexed color subrectangles) | Zlib compression level (raw subrectangles) | Palette threshold | Interframe comparison | Notes |
---|---|---|---|---|---|
0 | None | None | Subrectangle size / 4 | No | See the description of the “Lossless Tight” encoding method above. |
1 | 1 | 1 | Subrectangle size / 96 | No | See the description of the “Lossless Tight + Zlib” encoding method above. |
2-4 | 1 | 1 | Subrectangle size / 96 | No | Same as Compression Level 1 (reserved for future expansion) |
5 | None | None | Subrectangle size / 4 | Yes | Same as Compression Level 0, but with interframe comparison enabled |
6-8 | 1 | 1 | Subrectangle size / 96 | Yes | Same as Compression Level 1, but with interframe comparison enabled |
9 | 7 | 5 | Subrectangle size / 96 | Yes | 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 apps (and has no noticeable benefit for 3D and video apps.) Thus, its usefulness is generally very limited. |
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 server will send a mathematically lossless image of the current TurboVNC desktop to the requesting viewer. So, for instance, a user can rotate/pan/zoom an object in their 3D application using a very low-quality JPEG setting, then when that user is ready to interpret or analyze the object, they can request a lossless refresh of TurboVNC’s virtual screen.
To perform a lossless refresh, press CTRL-ALT-SHIFT-L (in the Windows and Java/Mac TurboVNC Viewers, you can also click on the Lossless Refresh toolbar icon.)
Passing an argument of
-alr
{timeout}
to
vncserver
will enable the automatic lossless refresh (ALR)
feature for the TurboVNC session. ALR will monitor all of the VNC
viewer connections, and if more than {timeout}
seconds have elapsed since the last framebuffer update was sent to a
given viewer, then the TurboVNC Server will send to 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 -alrqual
and -alrsamp
to
vncserver
to specify that automatic lossless refreshes
should be sent using JPEG instead (see the Xvnc
man page
for details.)
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.
The default is for any regions drawn with X[Shm]PutImage()
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 server to request that the
viewer move a rectangle of pixels from one location to another.) When
used with VirtualGL, this means that ALRs will mainly be sent for just
the 3D screen regions. This should be fine for most 3D applications,
since the 3D regions are the ones that are quality-critical. The
default ALR behavior also prevents what might best be called the
“blinking cursor dilemma.” Certain ill-behaved window
managers update a small region of the taskbar continuously, even though
none of the pixels in that region have changed. Also, 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 continuous updates
prevent an ALR from ever being sent. Fortunately, these ill-behaved
window managers and blinking cursors do not typically use
X[Shm]PutImage()
to perform their updates, so the problem
is effectively worked around by limiting the ALR-eligible regions to
just the subset of regions that were drawn with
X[Shm]PutImage()
and CopyRect.
You can override the default ALR behavior, thus making all screen
regions eligible for ALR, by setting the TVNC_ALRALL
environment variable to 1
on the TurboVNC server machine
prior to starting a TurboVNC session. You can also set
TVNC_ALRCOPYRECT
to 0
to make CopyRect regions
ALR-ineligible, which approximates the behavior of TurboVNC 1.2.1 and
prior.
The TurboVNC Server can use 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 multithreading the server will not help. It will almost certainly have no effect on networks slower than 100 Megabit Ethernet or when using the Java TurboVNC Viewer as an applet.
To enable server-side multithreading, set the TVNC_MT
environment variable to 1
on the server prior to starting
vncserver
. The default behavior is to use as many threads
as there are cores on the server machine, but you can set the
TVNC_NTHREADS
environment variable to override this.
The Java TurboVNC Viewer can be used as a standalone app, in which case
it provides most of the same features as the native TurboVNC viewers.
It can also load libjpeg-turbo through JNI to accelerate JPEG decoding,
which gives the Java viewer similar performance to the native viewers in
most cases. The TurboVNC Viewer on Mac platforms is simply the Java
TurboVNC Viewer packaged in such a way that it behaves like a native
viewer. On Windows and Linux/Un*x, the Java TurboVNC Viewer is packaged
similarly, but it is included alongside the native TurboVNC Viewer,
giving users a choice between the two. The Java TurboVNC Viewer
packaging includes the libjpeg-turbo JNI library, which is automatically
loaded when you launch the TurboVNC Viewer app on Mac, run the
vncviewer-java
script on Linux/Un*x, run the
vncviewer-java.bat
script on Windows, or launch “Java
TurboVNC Viewer” from the Windows Start Menu. Thus, if you are
running the Java TurboVNC Viewer in one of those ways, then no further
action is needed to accelerate it.
If you suspect for whatever reason that JPEG decoding is not being accelerated, then the easiest way to check is to open the “Connection Info” dialog (after the connection to the server has been established) and verify that the “JPEG decompression” field says “Turbo”. If you are launching the Java TurboVNC Viewer from the command line, then it will also print a warning if it is unable to load libjpeg-turbo.
When running the Java TurboVNC Viewer on Linux/Un*x platforms, it is
necessary to enable MIT-SHM Pixmap support in order to achieve optimal
blitting (image drawing) performance. MIT-SHM Pixmaps are not always
enabled by default on certain graphics cards (some nVidia cards, for
instance), and in such cases, it may be necessary to add an entry to
xorg.conf in order to enable them. The
vncviewer-java
script on Linux/Un*x platforms runs a helper
application to verify that MIT-SHM Pixmaps are available and working.
You can further verify that X11 blitting is being accelerated by running
java -Dsun.java2d.trace=count -cp /opt/TurboVNC/java/VncViewer.jar com.turbovnc.vncviewer.ImageDrawTest
Let the benchmark run for 15 or 20 seconds, then abort it with CTRL-C.
If you notice in the Java 2D trace output that there are no calls to
sun.java2d.x11.X11PMBlitLoops::Blit()
, then blitting is not
being accelerated, and the most likely reason is that MIT-SHM Pixmaps
are not enabled.
Sometimes the benchmark will report that the graphics device supports H/W acceleration even when it doesn’t. This is due to a bug in Java 2D. Thus, looking at the trace output is the only reliable way to determine whether or not X11 blitting is being accelerated.
Even with accelerated X11 blitting, the Java TurboVNC Viewer may not be quite as fast as the X11 TurboVNC Viewer on older, slower systems. This is because image drawing in Java 2D requires an extra memory copy that is not required when using raw X11 commands. However, on newer systems with fast memory access (particularly systems with a large L2 or L3 cache), this overhead should have a negligible impact on overall performance.
Passing an argument of -server
to java
when
launching the Java TurboVNC Viewer is recommended. This enables the
adaptive compiler, which performs aggressive code optimizations and
actually learns how to better optimize a piece of code the more times it
encounters it. Such optimizations greatly improve the decoding
performance for non-JPEG subrectangles. If you are launching the Java
TurboVNC Viewer using the Mac app, the vncviewer-java
or
vncviewer-java.bat
scripts, or the Windows Start Menu
shortcut, then the Server VM is automatically enabled.
Java Web Start can be used to deploy the Java TurboVNC Viewer and the associated libjpeg-turbo JNI libraries from a web server. Deploying the viewer using JWS provides a fully functional and performant TurboVNC Viewer environment without requiring the viewer to be installed on the client machine. This mechanism is preferred over deploying the viewer as an applet, since JPEG decoding cannot be accelerated when the Java TurboVNC Viewer is run as an applet. See http://www.TurboVNC.org/Documentation/JWS for more details.
The TurboVNC Server supports four “authentication methods”, which are used to validate authentication credentials sent from a VNC viewer:
vncpasswd
, a unique password is generated “on
the fly” for the TurboVNC session and is printed on the
server’s command line (see the man page for
vncpasswd
for more details.) The user enters this
password in the VNC viewer as if it were a VNC password, and the viewer
sends the OTP using the “Standard VNC” authentication
scheme (see below.) However, once the OTP has been used once to
authenticate a viewer, it 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 TurboVNC Viewer supports three “authentication schemes”, which are protocols used to validate authentication credentials with a VNC server:
The default behavior of the TurboVNC Server is for all authentication
methods to be enabled and for VNC password authentication and OTP to be
preferred over PAM user/password authentication. However, the system
administrator can disable one or more of the authentication methods or
set the preferred order of the authentication methods by editing the
server’s authentication configuration file. See the
Xvnc
man page for more details.
If the server allows multiple authentication methods that support
multiple authentication schemes, then the client’s default
authentication scheme will be determined by the preferred authentication
method on the server. In this case, the user can override the default
by passing command-line arguments to vncviewer
. If the
server prefers an authentication method that supports standard VNC
authentication, then the user can force the use of Unix login
authentication by passing an argument of
-user
{user_name}
to
vncviewer
when connecting to the TurboVNC session.
Similarly, if the server prefers an authentication method that supports
Unix login authentication, then the user can force the use of standard
VNC authentication by passing an argument of -nounixlogin
to vncviewer
. Both of these command-line options work with
all versions of the TurboVNC Viewer. When using the Java TurboVNC
Viewer, you can also accomplish the same thing by unchecking “Unix
Login” or “Standard VNC” in the “Security”
tab of the Options dialog. When using the Java TurboVNC Viewer as an
applet, you can accomplish the same thing by setting the
User
or NoUnixLogin
parameters in
/opt/TurboVNC/java/index.vnc
on the server.
If the system administrator has not restricted any of the authentication
methods on a system-wide basis, then the user can choose to disable some
or all of them for a single TurboVNC session by passing command-line
arguments to vncserver
. See the vncserver
man
page for more details.
For more detailed information about the TurboVNC authentication extensions, refer to the TurboVNC man pages:
man -M /opt/TurboVNC/man vncserver man -M /opt/TurboVNC/man Xvnc man -M /opt/TurboVNC/man vncviewer man -M /opt/TurboVNC/man vncpasswd
Referring to the VirtualGL User’s Guide, VirtualGL’s X11 Transport draws 3D images onto an X display using standard X11 drawing commands. Since this results in the images 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 the application (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.
Since VirtualGL is sending rendered 3D images to the X proxy at a very fast rate, the proxy must be able to compress the images very quickly in order to keep up. Unfortunately, however, most X proxies can’t. They simply aren’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 3D images from VirtualGL to a client machine without using VirtualGL’s embedded VGL Transport.
The most common (and optimal) way to use TurboVNC is to set it up on the same server that is running VirtualGL. This allows VirtualGL to send its rendered 3D images to TurboVNC through shared memory rather than sending them over a network.
The following procedure describes how to launch a 3D application using this configuration.
/opt/VirtualGL/bin/vglrun [vglrun options] {application_executable_or_script} {arguments}The TurboVNC startup script sets the
VGL_COMPRESS
environment variable to 0
, which will automatically enable
the X11 Transport within VirtualGL.
If TurboVNC and VirtualGL are running on different servers, then it is desirable to use the VGL Transport to send images from the VirtualGL server to the TurboVNC server. 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 server for this procedure to perform well.
/opt/VirtualGL/bin/vglconnect {user}@{server}Replace
{user}
with your username on the VirtualGL
server and {server}
with the hostname or IP
address of that server. Refer to the VirtualGL User’s Guide for
additional vglconnect
options.
VGL_COMPRESS
environment
variable to rgb
Passing an argument of -c rgb
to vglrun
achieves the same effect.
/opt/VirtualGL/bin/vglrun [vglrun options] {application_executable_or_script} {arguments}
In order to realize the full performance benefits of TurboVNC, it is necessary to use a TurboVNC server and a TurboVNC viewer in concert. However, TurboVNC is fully 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.
The following sections list additional things to bear in mind when mixing TurboVNC with other VNC flavors.
JPEG quality level | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 |
---|---|---|---|---|---|---|---|---|---|---|
Actual JPEG quality | 5 | 10 | 15 | 25 | 37 | 50 | 60 | 70 | 75 | 80 |
Actual chrominance subsampling | 2X | 2X | 2X | 2X | 2X | 2X | 2X | 2X | 2X | 2X |
JPEG quality level | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 |
---|---|---|---|---|---|---|---|---|---|---|
Actual JPEG quality | 15 | 29 | 41 | 42 | 62 | 77 | 79 | 86 | 92 | 100 |
Actual chrominance subsampling | 4X | 4X | 4X | 2X | 2X | 2X | 1X | 1X | 1X | 1X |
Average compression ratio * | 100 | 80 | 70 | 60 | 50 | 40 | 30 | 25 | 20 | 10 |
* Experimentally determined by compressing every 10th frame in the SPECviewperf 9 benchmark suite
The TurboVNC Viewer supports the Hextile and Raw encoding types, which are compatible with RealVNC. The Java/Mac TurboVNC Viewer additionally supports ZRLE and RRE. None of these encoding types can be selected from the TurboVNC Viewer GUI, but Hextile or ZRLE will be selected automatically when connecting to a RealVNC server. Raw will be automatically selected when connecting to a VNC server running on the same machine as the viewer. Non-Tight encoding types, such as Hextile and Raw, can also be manually selected from the TurboVNC Viewer command line. In addition to Hextile, Raw, ZRLE, and RRE, the TurboVNC Server also supports the CoRRE and Zlib legacy encoding types, for compatibility with older VNC viewers.
All of the non-Tight encoding types have performance drawbacks. Raw
encoding requires gigabit in order to achieve decent performance, and it
can easily take up an entire gigabit connection’s worth of
bandwidth. 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 links but uses too much CPU time to perform well on
fast links. ZRLE improves upon this, but it is still too
computationally intense for fast networks. The
vncviewer-java
man page in the TurboVNC Linux packages has
some additional information about how Hextile, RRE, and ZRLE work.
Environment Variable | TVNC_ALRALL = 0 | 1 |
Summary | Disable/Enable automatic lossless refresh for regions that were drawn using X11 functions other than X[Shm]PutImage() |
Default Value | Disabled |
Environment Variable | TVNC_ALRCOPYRECT = 0 | 1 |
Summary | Disable/Enable automatic lossless refresh for regions that were drawn using CopyRect |
Default Value | Enabled |
Environment Variable | TVNC_COMBINERECT = {c} |
Summary | Combine framebuffer updates with more than {c} rectangles into a single rectangle spanning the bounding box of all of the constituent rectangles |
Default Value | 100 |
{c}
rectangles, TurboVNC will
coalesce it into a single rectangle that covers all of the rectangles in
the update. For applications that generate many tiny rectangles,
increasing TVNC_COMBINERECT
may significantly increase the
number of pixels sent to the viewer, which will increase network usage.
However, for those same applications, lowering
TVNC_COMBINERECT
will increase the number of rectangles
sent to the viewer, which will increase the CPU usage of both the server
and the viewer.
Environment Variable | TVNC_IFDEBUG = 0 | 1 |
Summary | Disable/Enable the ICE debugger |
Default Value | Disabled |
Environment Variable | TVNC_MT = 0 | 1 |
Summary | Disable/Enable multithreaded image encoding |
Default Value | Disabled |
Environment Variable | VGL_NTHREADS = {n} |
Summary | Use {n} threads to perform image encoding |
Default Value | {n} = the number of CPU cores in the system |
Environment Variable | TVNC_PROFILE = 0 | 1 |
Summary | Disable/enable profiling output |
Default Value | Disabled |
Environment Variable | TVNC_PROFILE = 0 | 1 |
Summary | Disable/enable profiling output |
Platforms | X11, Mac/Java |
Default Value | Disabled |