computer science

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Virtual Network Computing
VNC

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Outline
• What is VNC?
• Why do we need to be familiar with VNC?
• Where do we get VNC?
• Limitations of VNC?
• Other notes about VNC?

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What is VNC?
• Virtual Network Computing (VNC)
• Remote control system of other computer
windowing environments
• Allows access to “desktops” of like or
different operating systems
• Developed by AT&T Laboratories
• Freely Available
UNIX Windows
Mac

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Why VNC?
• Freedom to choose your favorite computing
environment
– And still have access to the more powerful UNIX
system
• Remote access is made possible to the major
platforms
– You want to work at home, but you forgot that one
critical file at school on the…
• Reinforces the concepts of client/server
software
– Concept foreign to most PC/MAC users
• Price is right
– Free

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Where to get VNC?
• AT&T Laboratories, Cambridge UK
http://www.uk.research.att.com/vnc/
• Available for UNIX environment
– Requires system administrator privileges
– Already installed on the CIS machines
• Available for Windows platform
– Requires you to download and install on your
machine
• Available for Mac platform
• Available for Java-enabled browsers

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Limitations of VNC
• VNC is network resource intensive
– High Bandwidth connection = Good situation
– Low Bandwidth connection = Bad situation
• Filesystems are still separate between
different operating systems
– Transferring files still requires other mechanisms
(e.g. ftp)
• Access to non-Unix platforms do not have
good multi-user support
– PC/MAC lack general concept of several user
access

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Quickstart use of VNC
• Prerequisites
– You should be comfortable with the client/server
concepts of the X-windows environment
– If not, review “Introduction to X windows”
» http://www.strath.ac.uk:80/CC/Courses/oldXC/xc.html
– VNC server and viewer installed on both local and
remote machines
• Configurations you will encounter
1. Local PC/MAC accessing remote UNIX system
2. Local UNIX system accessing remote PC/MAC
3. Local UNIX system accessing remote UNIX
system

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Installation of VNC Software
• Download site
– http://www.uk.research.att.com/vnc/download.html
• CIS Unix platforms
– Already installed by system administrator
• PC platform
– Download and install as you would other PC
software
• Mac platform
– Download and install as you would other Mac
software

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VNC Software components
• VNC has two major software components
vncserver
vncviewer

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VNCSERVER
• Provides the “remote” half of the “remote
control” system
• Communicates interactions from the remote
machine to the local machine
• Exports the view of the remote “deskstop”
screen environment to a local machine
• Imports keyboard and mouse inputs from local
machine to remote machine

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VNCVIEWER
• Provides the “local” half of the “remote
control” system
• Communicates interactions between local
machine to the remote machine
• Imports the view of the remote “deskstop”
screen environment to the local machine
• Exports keyboard and mouse inputs from local
machine to remote machine

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Local PC/Mac Accessing Remote
CIS SUN UNIX System
• Prerequisites
– Assumes you have a UNIX account on CIS system
– Assumes you have downloaded and installed VNC
on your local PC/Mac
• Use “telnet” to login to a SUN UNIX system
% telnet armstrong.cis.rit.edu
• Make sure remote machine is a SUN platform
% uname -a
SunOS armstrong 5.7 ...

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PC/MAC accessing UNIX
(starting server for the first time)
• Start the server software on the UNIX side for
the first time will ask you for a password
% vncserver
• This password does not need to be the same
as your UNIX password
• This password is used only during
authentication when you connect using VNC
• You can change this password using
% vncpasswd

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PC/MAC accessing UNIX
(starting the server)
• Start the server software on the UNIX side
% vncserver
New 'X' desktop is armstrong:1
Starting app... in ~rvrpci/.vnc/xstartup
Log file is ~rvrpci/.vnc/armstrong:1.log

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PC/MAC accessing UNIX
(meaning of server messages)
• Name of exported “virtual desktop window” is
armstrong:1
New 'X' desktop is armstrong:1
• The specific X-window manager and
associated startup applications is specified by
the file below (view using text editor)
Starting app... in ~rvrpci/.vnc/xstartup
• Any informational or error messages are
logged in the file below (view using text editor)
Log file is ~rvrpci/.vnc/armstrong:1.log

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PC/MAC access UNIX
(start the viewer)
• Invoke “vncviewer” application
– Double click on vncviewer icon or
– “Start->Programs->VNC->Run VNCviewer”
• You will be prompted for a remote host name
to control
– e.g. armstrong:1
• You will be prompted for a VNC password
• If successful, you should get a window with a
view

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PC/MAC accessing UNIX
(windows with a view)

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PC/MAC accessing UNIX
(shutting down the server)
% vncserver -kill :1
Killing Xvnc process ID 10733
• Above command kills the virtual window, in
this case, armstrong:1
• If you do not kill the server, but kill the viewer,
you can always reconnect from another viewer
and pick up where you left off
– Frowned upon by the system administrator if
abused (SA has prerogative to kill your desktop)

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UNIX accessing PC/MAC Desktop
• Prerequisites
– VNC software installed on UNIX and remote
PC/MAC
– Owner of PC/MAC has given you VNC password
– Vncserver running on PC
• Start vncviewer
% vncviewer
• Enter PC/MAC VNC server name to access
• Enter PC/MAC VNC password

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UNIX accessing PC/MAC Desktop
(X-windows with a view)

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UNIX Desktop to UNIX Desktop
Access
• Rarely done using VNC because X-windows
already provides this capability
– VNC only adds overhead
• VNC may be used to save desktop
environments from session to session
• Procedure similar to PC/MAC to UNIX desktop
access

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PC/MAC to PC/MAC Access
• Prerequisites similar to PC/MAC to UNIX
access
• Be careful interfering with someone working
on the remote machine
– It is possible to disable remote keyboard and
mouse
• PC to PC access allows
– Limited remote troubleshooting of PC system
– Multiple viewers to “listen in” on one window

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Other means of VNC access
• Java-enabled browser can access any
vncserver
• For example, access to armstrong:1
http://armstrong:5801
http://armstrong.cis.rit.edu:5801
• Or access to armstrong:2
http://armstrong:5802
http://armstrong.cis.rit.edu:5802
• Successful connection will be followed by
VNC password authentication

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Browser Access to VNC server

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When in doubt about vncserver
under UNIX…
bean% vncserver -h
usage: vncserver [:<number>]
[-name <desktop-name>] [-depth <depth>]
[-geometry <width>x<height>]
[-pixelformat rgbNNN|bgrNNN]
<Xvnc-options>...
vncserver -kill <X-display>

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When in doubt about vncviewer
under UNIX
bean% vncviewer -h
VNC viewer version 3.3.3r1
usage: vncviewer [<options>] <host>:<display#>
vncviewer [<options>] -listen [<display#>]
<options> are standard Xt options, or:
-shared
-viewonly
-fullscreen
-passwd <passwd-file>
-encodings <encoding-list> (e.g. "raw copyrect")
-bgr233
-owncmap
-truecolour
-depth <depth>

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Key VNC Options to consider
% vncserver -depth 24
– Starts up your server in 24-bit mode color mode
% vncviewer -share -viewonly
– First option
» Starts up your viewer so that others can also see the
server
» Useful for having two or more people control the desktop
– Second option
» Makes sure that you can only see the desktop and not
control it
» Particularly useful in a group environment when you want
only one person to “drive”

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Other VNC considerations
• Cutting and pasting text information
– Supported between remote and local windows
• Provides a foundation for CSCW
– Computer Supported Cooperative Work
• Source code freely available
– Other platforms are actively being included
• VNC performance can be an issue, but
– Beats driving through the snow to school to pick up
that one #@$%^ data file