Xen users - Dec 2009 - Vnc unable to open Display on xen CentOS

I am getting following error while establishing a VNC connection on the
machine
[root@xen ~]# vncviewer localhost:0

VNC Viewer Free Edition 4.1.2 for X - built Mar 24 2009 19:52:30
Copyright (C) 2002-2005 RealVNC Ltd.
See http://www.realvnc.com for information on VNC.
vncviewer: unable to open display ""
What should I look in for.



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On Tue, Dec 22, 2009 at 3:32 PM, Tapas Mishra <tapas@abhitech.com>
wrote:
> vncviewer: unable to open display ""
this pretty much says it all. Most likekly you need to have X
forwarding enabled (if connecting via ssh).
Another possibilty is that if you login as normal user and run "su -".
In this case, simply run the command as normal user. You don''t need
super user priviledge to run vncviewer.

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On Tue, Dec 22, 2009 at 2:05 PM, Fajar A. Nugraha <fajar@fajar.net> wrote:
> On Tue, Dec 22, 2009 at 3:32 PM, Tapas Mishra <tapas@abhitech.com>
wrote:
> > vncviewer: unable to open display ""
>
> this pretty much says it all. Most likekly you need to have X
>
I am not clear with this can you tell me some thing about this one
> forwarding enabled (if connecting via ssh).
>
Ya I am doing it via ssh Only
> Another possibilty is that if you login as normal user and run "su
-".
> In this case, simply run the command as normal user. You don''t
need
> super user priviledge to run vncviewer.
>
> --
> Fajar
>

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On Tue, Dec 22, 2009 at 3:38 PM, Tapas Mishra <tapas@abhitech.com>
wrote:
>> > vncviewer: unable to open display ""
>>
>> this pretty much says it all. Most likekly you need to have X
>
> I am not clear with this can you tell me some thing about this one
Are you familiar with X display? X forwarding? If no, you should
search for that first.
>>
>> forwarding enabled (if connecting via ssh).
>
> Ya I am doing it via ssh Only
>From a windows machine?
If yes, Google for "windows ssh X forwarding". Something like this
http://solaris.reys.net/how-to-x11-forwarding-using-ssh-putty-and-xming/

Another alternative is to edit domU config file to accept vnc
connections on all IP instead of localhost. Not secure, but handy for
testing purposes. This way you can simply install vnc client on
Windows and connect directly.

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I do not have any windows machine with me my Xen is on CentOS and rest all
are Ubuntu machines I had been able to do a vnc from CentOS to Ubuntu
machines but not vice versa I have an understanding of X forwarding but
still it I could not do it ,so I wanted to figure out where the error was
but I will search more as you said

On Tue, Dec 22, 2009 at 2:21 PM, Fajar A. Nugraha <fajar@fajar.net> wrote:
> On Tue, Dec 22, 2009 at 3:38 PM, Tapas Mishra <tapas@abhitech.com>
wrote:
> >> > vncviewer: unable to open display ""
> >>
> >> this pretty much says it all. Most likekly you need to have X
> >
> > I am not clear with this can you tell me some thing about this one
>
> Are you familiar with X display? X forwarding? If no, you should
> search for that first.
>
> I do not have any windows machine with me my Xen is on CentOS and rest all
> are Ubuntu machines I had been able to do a vnc from CentOS to Ubuntu
> machines but not vice versa I have an understanding of X forwarding but
> still it I could not do it ,so I wanted to figure out where the error was
> but I will search more as you said
>
> >>
> >> forwarding enabled (if connecting via ssh).
> >
> > Ya I am doing it via ssh Only
>
> From a windows machine?
> If yes, Google for "windows ssh X forwarding". Something like
this
> http://solaris.reys.net/how-to-x11-forwarding-using-ssh-putty-and-xming/
>
> Another alternative is to edit domU config file to accept vnc
> connections on all IP instead of localhost. Not secure, but handy for
> testing purposes. This way you can simply install vnc client on
> Windows and connect directly.
>
> Thanks for these links
but can you point me to the right log file which I should check in the case
of failures of X forwarding on SSH that should be able to help me a bit.



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On Tue, Dec 22, 2009 at 4:12 PM, Tapas Mishra <tapas@abhitech.com>
wrote:
> I do not have any windows machine with me my Xen is on CentOS and rest all
> are Ubuntu machines
Let me rephrase the question. Where are you ssh-ing the server from? A
Windows notebook? Mac? Ubuntu? Once you have that, you can search
Google on how to enable ssh forwarding when using that particular
CLIENT OS. Most linux distros that I know of already enable X
forwarding on server side, so it''s usually just a matter of
configuring the client.
> Thanks for these links
> but can you point me to the right log file which I should check in the case
> of failures of X forwarding on SSH that should be able to help me a bit.
not much. Basically when you have that error unable to open display
"", and you''re connecting via ssh, then most likely its ssh
forwarding
problem. Sometimes it''s as simple to fix as running "ssh -X"
instead
of just ssh.

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>
> Let me rephrase the question. Where are you ssh-ing the server from? A
> Windows notebook? Mac? Ubuntu? Once you have that, you can search
> Google on how to enable ssh forwarding when using that particular
> CLIENT OS. Most linux distros that I know of already enable X
> forwarding on server side, so it''s usually just a matter of
> configuring the client.
>
Ok I am using a Ubuntu Laptop as client


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On Tue, Dec 22, 2009 at 4:33 PM, Tapas Mishra <tapas@abhitech.com>
wrote:
>> Let me rephrase the question. Where are you ssh-ing the server from? A
>> Windows notebook? Mac? Ubuntu? Once you have that, you can search
>> Google on how to enable ssh forwarding when using that particular
>> CLIENT OS. Most linux distros that I know of already enable X
>> forwarding on server side, so it''s usually just a matter of
>> configuring the client.
>
> Ok I am using a Ubuntu Laptop as client
using "ssh -X" should be enough. Another way is to edit
/etc/ssh/ssh_config, look for ForwardX11

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>
>
> using "ssh -X" should be enough. Another way is to edit
> /etc/ssh/ssh_config, look for ForwardX11
I have done a lot of things which have not worked one of them being
following
I followed this one http://wiki.centos.org/HowTos/VNC-Server

 ssh root@192.168.1.10 <root@188.95.37.130> -L 5901:localhost:5901
root@192.168.1.10 <root@188.95.37.130>’s password:
bind: Address already in use
channel_setup_fwd_listener: cannot listen to port: 5901
Could not request local forwarding.
Last login: Tue Dec 22 15:01:10 2009 from 192.168.1.1

tapas@tapas-laptop:~$ vncviewer 192.168.1.10
192.168.1.10 5900
java.net.ConnectException: Connection refused
at java.net.PlainSocketImpl.socketConnect(Native Method)
at java.net.PlainSocketImpl.doConnect(PlainSocketImpl.java:333)
at java.net.PlainSocketImpl.connectToAddress(PlainSocketImpl.java:195)
at java.net.PlainSocketImpl.connect(PlainSocketImpl.java:182)
at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:366)
at java.net.Socket.connect(Socket.java:525)
at java.net.Socket.connect(Socket.java:475)
at java.net.Socket.(Socket.java:372)
at java.net.Socket.(Socket.java:186)
at rfbProto.(rfbProto.java:93)
at vncviewer.connectAndAuthenticate(vncviewer.java:193)
at vncviewer.run(vncviewer.java:122)
at java.lang.Thread.run(Thread.java:619)
java.net.ConnectException: Connection refused


Other way which I tried was
>From the CentOS Wiki http://wiki.centos.org/HowTos/VNC-Server
I read and did
Here is what I did
added a user tapas  on 192.168.1.10
for using vnc


VNCSERVERS="1:tapas"
VNCSERVERARGS[1]="-geometry 640x480"
also did # service vncserver start
went to /home/tapas/.vnc and edited
xstartup
removed the comment from these two lines
unset SESSION_MANAGER
exec /etc/X11/xinit/xinitrc
also added following lines to the start of the file
( while true ; do xterm ; done ) &
So that xterm session is available
restarted vncserver
service vncserver restart



But VNC Server is running which we can verify from the following outcome

vncext: VNC extension running!
vncext: Listening for VNC connections on port 5902
vncext: Listening for HTTP connections on port 5802
vncext: created VNC server for screen 0
error opening security policy file /usr/lib64/xserver/SecurityPolicy
/home/tapas/.vnc/xstartup: line 9: xsetroot: command not found
/home/tapas/.vnc/xstartup: line 11: xterm: command not found
/home/tapas/.vnc/xstartup: line 12: twm: command not found
Could not init font path element unix/:7100, removing from list!


Connections: accepted: 192.168.1.3::56069
SConnection: Client needs protocol version 3.8
SConnection: Client requests security type VncAuth(2)

Tue Dec 22 23:07:48 2009
VNCSConnST: Server default pixel format depth 16 (16bpp) little-endian
rgb565
VNCSConnST: Client pixel format depth 16 (16bpp) little-endian rgb565


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On Wed, Dec 23, 2009 at 10:14 AM, Tapas Mishra <tapas@abhitech.com>
wrote:
>>
>> using "ssh -X" should be enough. Another way is to edit
>> /etc/ssh/ssh_config, look for ForwardX11
>
> I have done a lot of things which have not worked one of them being
> following
> I followed this one http://wiki.centos.org/HowTos/VNC-Server
Sorry, at this point I have to ask, are you reading my replies correctly?
I never suggested that you setup vnc SERVER. When setup correctly
(like when using virt-manager/virt-install), domU is already setup
with a vnc console. You don''t need to setup vnc server manually.

What I suggested was :
- setup X forwarding correctly.
Since you said you use ubuntu and connect via ssh, the simplest method
is to run "ssh -X root@192.168.1.10" instead of just "ssh
root@192.168.1.10" (I assume your server IP is 192.168.1.10?). OR,

- edit domU config file to enable vnc access from any IP address
instead of just localhost.
The corresponding entry is "vnclisten" (for HVM domUs) or
"vfb" (for
PV domUs). Use "xm create --help_config" to find more help about those
entries. After this, you need install vnc CLIENT on your Ubuntu laptop
(on Ubuntu the package can be vncviewer, xtightvncviewer, or
xvnc4viewer), then run (on your laptop) "vncviewer 192.168.1.10:0" (or
whatever the vnc display number is).


To be fair, there ARE solutions than can allow you to view domUs
console that requires installing vnc server on dom0 first, but if you
want to use this solution, then you''re on your own. I can''t
help you
with that, since IMHO it''s too much hassle to setup than what
it''s
worth.

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On Wed, Dec 23, 2009 at 9:07 AM, Fajar A. Nugraha <fajar@fajar.net> wrote:
> On Wed, Dec 23, 2009 at 10:14 AM, Tapas Mishra <tapas@abhitech.com>
wrote:
> >>
> >> using "ssh -X" should be enough. Another way is to edit
> >> /etc/ssh/ssh_config, look for ForwardX11
> >
> > I have done a lot of things which have not worked one of them being
> > following
> > I followed this one http://wiki.centos.org/HowTos/VNC-Server
>
> Sorry, at this point I have to ask, are you reading my replies correctly?
> I never suggested that you setup vnc SERVER. When setup correctly
> (like when using virt-manager/virt-install), domU is already setup
> with a vnc console. You don''t need to setup vnc server manually

I agree with you here but the machine to which I am having access I does not
have an X or say GNOME Desktop manager present

> .
>
> What I suggested was :
> - setup X forwarding correctly.
> Since you said you use ubuntu and connect via ssh, the simplest method
> is to run "ssh -X root@192.168.1.10" instead of just "ssh
>
I have tried this one also though I forgot to post it here

> To be fair, there ARE solutions than can allow you to view domUs
> console that requires installing vnc server on dom0 first, but if you
> want to use this solution, then you''re on your own. I
can''t help you
> with that, since IMHO it''s too much hassle to setup than what
it''s
> worth.
>
Well thanks for the answers you gave I appreciate the efforts that you have
put in here.
>
>

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On Wed, Dec 23, 2009 at 3:01 PM, Tapas Mishra <tapas@abhitech.com>
wrote:
>> Sorry, at this point I have to ask, are you reading my replies
correctly?
>> I never suggested that you setup vnc SERVER. When setup correctly
>> (like when using virt-manager/virt-install), domU is already setup
>> with a vnc console. You don''t need to setup vnc server
manually
>
> I agree with you here but the machine to which I am having access I does
not
> have an X or say GNOME Desktop manager present
You don''t need gnome desktop on the server to display domU''s
console.

If you want to have gnome desktop on the server (which is a different
problem altogether), I recommend installing it with yum, and use
something like NX (http://www.nomachine.com/) or xrdp. I find them
easier to setup, plus they can have persistent session much like
Windows remote desktop. This list is probably not a right place to
discuss the details though, so I''ll leave it at that.

>> Since you said you use ubuntu and connect via ssh, the simplest method
>> is to run "ssh -X root@192.168.1.10" instead of just
"ssh
>
> I have tried this one also though I forgot to post it here
Does it work?

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On Wed, Dec 23, 2009 at 2:49 PM, Fajar A. Nugraha <fajar@fajar.net> wrote:
> On Wed, Dec 23, 2009 at 3:01 PM, Tapas Mishra <tapas@abhitech.com>
wrote:
> >> Sorry, at this point I have to ask, are you reading my replies
> correctly?
> >> I never suggested that you setup vnc SERVER. When setup correctly
> >> (like when using virt-manager/virt-install), domU is already setup
> >> with a vnc console. You don''t need to setup vnc server
manually
> >
> > I agree with you here but the machine to which I am having access I
does
> not
> > have an X or say GNOME Desktop manager present
>
> You don''t need gnome desktop on the server to display
domU''s console.
>
> If you want to have gnome desktop on the server (which is a different
> problem altogether), I recommend installing it with yum, and use
> something like NX (http://www.nomachine.com/) or xrdp. I find them
> easier to setup, plus they can have persistent session much like
> Windows remote desktop. This list is probably not a right place to
> discuss the details though, so I''ll leave it at that.
>
> Well thanks
>
> >> Since you said you use ubuntu and connect via ssh, the simplest
method
> >> is to run "ssh -X root@192.168.1.10" instead of just
"ssh
> >
> > I have tried this one also though I forgot to post it here
>
> Does it work?
>
It works  I am having one test CentOS  machine where all the Gnome etc was
installed so this do work but then on the machine where there is no X
environment it does not works any how thanks for all the help.



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On Wed, Dec 23, 2009 at 4:23 PM, Tapas Mishra <tapas@abhitech.com>
wrote:
>> >> Since you said you use ubuntu and connect via ssh, the
simplest method
>> >> is to run "ssh -X root@192.168.1.10" instead of just
"ssh
>> >
>> > I have tried this one also though I forgot to post it here
>>
>> Does it work?
>
> It works  I am having one test CentOS  machine where all the Gnome etc was
> installed so this do work but then on the machine where there is no X
> environment it does not works any how thanks for all the help.
If I remember correctly you don''t need full blown gnome desktop for it
to work. On my system I added this packages (via "yum install", so
their dependencies will be installed)

xorg-x11-fonts-100dpi
xorg-x11-fonts-75dpi
xorg-x11-fonts-Type1
xorg-x11-fonts-base
xorg-x11-fonts-misc
xorg-x11-fonts-truetype
xorg-x11-server-Xorg
xorg-x11-xauth

not really sure which one is absolutely required on the server to get
X forwarding to work (perhaps just "yum install xorg-x11-xauth" will
do). If you want full-blown gnome desktop anyway, do

yum groupinstall "GNOME Desktop Environment"

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>
>
> not really sure which one is absolutely required on the server to get
>
If you wish I can post the log file we need to see to do all this but then
that is not what this community is meant for  the discussion is going in
another direction.
> X forwarding to work (perhaps just "yum install xorg-x11-xauth"
will
> do). If you want full-blown gnome desktop anyway, do
>
> yum groupinstall "GNOME Desktop Environment"
>
Yes I have done the same.



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Finally its working I have been able to transfer display over ssh Fajar
thanks for all the time you spent
the problem was on Ubuntu machine as root DISPLAY variable is not set
then in xstartup file for vnc user exec gnome-session has to be mentioned
which I forgot
I did yum groupinstall "X Window System" "GNOME Desktop
Environment"
as it was not present on the remote Xen machine
ubuntu does not allow root to use GUI so I was not able to do it again and
again DISPLAY was not set in this case for root
but for user it works fine
there were a lot of errors like this one

when vnc session crashed

Thu Dec 24 16:43:35 2009
 CConn:       connected to host localhost port 5901
 CConnection: Server supports RFB protocol version 3.8
 CConnection: Using RFB protocol version 3.8

Thu Dec 24 16:43:48 2009
 TXImage:     Using default colormap and visual, TrueColor, depth 24.
 CConn:       Using pixel format depth 6 (8bpp) rgb222
 CConn:       Using ZRLE encoding
X Error of failed request:  BadValue (integer parameter out of range for
operation)
  Major opcode of failed request:  140 (MIT-SHM)
  Minor opcode of failed request:  3 (X_ShmPutImage)
  Value in failed request:  0x400
  Serial number of failed request:  523
  Current serial number in output stream:  716


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