Xen users - Jan 2008 - Problem setting up VNC on SLES10 HVM DomU

I''ve just uneventfully installed SLES10 as an HVM DomU (after finding 
out, the hard way, that OpenSUSE 10.3 won''t install on Intel VT).

This almost went without a hitch, but I''ve been banging my head against
a brick wall for a few hours trying to get VNC working. I can get a 
remote desktop, but a few seconds after I log in to the remote desktop, 
the screen goes blank (just after I get the "Suse linux enterprise 10"
screen). Bizarrely, the SLES10 screen saver *does* appear on the remote 
desktop a few minutes later. Another odd thing is that the SDL window on 
my Dom0 has exactly the same behaviour: when I log in on the remote vnc 
client, I get some startup activity on the SDL window for a few seconds, 
and then it goes blank. The screensaver starts on the SDL window at the 
same time as on the vnc client. The only way I can talk to the DomU is 
on ssh.

Any ideas? I''m pretty sure that the vnc setup is correct on the DomU. 
I''ve enabled it via ''remote administration'' on YaST,
xinetd is running,
I can mod /etc/xinetd.d/vnc, etc (and I can log in anyway, so it must 
basically be working).

I''m using a realVNC client, but SLES appears to use tightVNC. I
don''t
think this is a problem. I can start a local tightVNC viewer on the DomU 
(with ssh -X), and it has exactly the same behaviour as the remote one 
(though possibly without the screensaver).

Another potential issue is that the relevant stuff on Google generally 
talks about using xdm, but SLES10 uses gdm by default, although I can''t
see how this could be relevant.

Any thoughts? /etc/sysconfig/displaymanager currently contains (I''ve 
tried some variants):

DISPLAYMANAGER="gdm"
DISPLAYMANAGER_REMOTE_ACCESS="yes"
DISPLAYMANAGER_ROOT_LOGIN_REMOTE="yes"
DISPLAYMANAGER_STARTS_XSERVER="yes"
DISPLAYMANAGER_XSERVER_TCP_PORT_6000_OPEN="yes"
DISPLAYMANAGER_AUTOLOGIN="evan"
DISPLAYMANAGER_PASSWORD_LESS_LOGIN="no"
DISPLAYMANAGER_AD_INTEGRATION="no"
DISPLAYMANAGER_SHUTDOWN="root"

Thanks -

Evan

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Can''t get an xdmcp chooser either. xdmcp is enabled in gdm.conf, port 
177 is open, turned off apparmor just in case, hosts.allow and 
hosts.deny are empty, and after all that a remote chooser still can''t 
see this DomU. The chooser has no problem with RedHat DomU''s with
nearly
identical gdm.confs.

- Evan

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No solutions, just some comments:

On Sunday 27 January 2008 05:11:57 am Evan Lavelle
wrote:
> I''ve just uneventfully installed SLES10 as an HVM DomU (after
finding
> out, the hard way, that OpenSUSE 10.3 won''t install on Intel VT).
I would be very surprised if 10.3 didn''t support Intel VT,
altho'' I''ve only
done SuSE PV installs. Where does it hang, during boot of the cd/iso?
> This almost went without a hitch, but I''ve been banging my head
against
> a brick wall for a few hours trying to get VNC working. I can get a
> remote desktop, but a few seconds after I log in to the remote desktop,
> the screen goes blank (just after I get the "Suse linux enterprise
10"
> screen). Bizarrely, the SLES10 screen saver *does* appear on the remote
> desktop a few minutes later. Another odd thing is that the SDL window on
> my Dom0 has exactly the same behaviour: when I log in on the remote vnc
> client, I get some startup activity on the SDL window for a few seconds,
> and then it goes blank. The screensaver starts on the SDL window at the
> same time as on the vnc client. The only way I can talk to the DomU is
> on ssh.
Presumably you have done the Gnome System -> Preferences -> Look and Feel
->
Screensaver (gnome-screensaver-preferences), and -> System -> Power 
Management (gnome-power-preferences) things, and make sure your timeouts are 
suitably large, or disabled. Run the program in parenthesis in a ''ssh
-X''
session from a remote client if your desktop is totally unresponsive. If you 
move your mouse after the screensaver comes on, does your desktop come back 
to life? If SDL, vnc, and xdmcp all bring up a screensaver, something must be 
wrong with your timeouts.
> Any ideas? I''m pretty sure that the vnc setup is correct on the
DomU.
> I''ve enabled it via ''remote administration'' on
YaST, xinetd is running,
> I can mod /etc/xinetd.d/vnc, etc (and I can log in anyway, so it must
> basically be working).
Xinetd implies your vnc server is on the domu, instead of the dom0. Have you 
tried the vnc server built into qemu-dm? (vncviewer localhost:port#)
> Any thoughts? /etc/sysconfig/displaymanager currently contains
(I''ve
> tried some variants):
>
> DISPLAYMANAGER="gdm"
> DISPLAYMANAGER_REMOTE_ACCESS="yes"
> DISPLAYMANAGER_ROOT_LOGIN_REMOTE="yes"
> DISPLAYMANAGER_STARTS_XSERVER="yes"
> DISPLAYMANAGER_XSERVER_TCP_PORT_6000_OPEN="yes"
> DISPLAYMANAGER_AUTOLOGIN="evan"
> DISPLAYMANAGER_PASSWORD_LESS_LOGIN="no"
> DISPLAYMANAGER_AD_INTEGRATION="no"
> DISPLAYMANAGER_SHUTDOWN="root"
You realize this refers to xdmcp, not vnc, right?
> Can''t get an xdmcp chooser either. xdmcp is enabled in gdm.conf,
port
> 177 is open, turned off apparmor just in case, hosts.allow and 
> hosts.deny are empty, and after all that a remote chooser still
can''t
> see this DomU. The chooser has no problem with RedHat DomU''s with
nearly
> identical gdm.confs.
My experience with chooser boxes is that they may not see all available hosts 
on a scan, but if you type in the hostname, you can connect. Make sure your 
firewalls on domu and remote client are open, or off. I use ''sudo
iptraf'' to
see who is not responding during attempted communications.

Sorry I couldn''t provide a definitive answer - just go over the basics
again.
Good luck.

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Some progress - I can connect over anything (xdmcp, vnc, sdl) if I logon 
as root, but not otherwise. However, it can''t be an authentication 
problem, since I get well beyond the login screen if I log in as myself. 
The display doesn''t blank until just before it creates the panel at the
bottom. I suspect it may be something to do with the gdm PreSession 
scripts, but I can''t see any obvious problems.

jim burns wrote:
> I would be very surprised if 10.3 didn''t support Intel VT,
altho'' I''ve only
> done SuSE PV installs. Where does it hang, during boot of the cd/iso?
Yes; seems to be a known problem - see these 2:

http://www.mail-archive.com/fedora-xen@redhat.com/msg00699.html
http://lists.xensource.com/archives/html/xen-devel/2007-12/msg00564.html
> Presumably you have done the Gnome System -> Preferences -> Look and
Feel ->
> Screensaver (gnome-screensaver-preferences), and -> System -> Power 
> Management (gnome-power-preferences) things, and make sure your timeouts
are
> suitably large, or disabled. Run the program in parenthesis in a
''ssh -X''
> session from a remote client if your desktop is totally unresponsive. If
you
> move your mouse after the screensaver comes on, does your desktop come back
> to life? If SDL, vnc, and xdmcp all bring up a screensaver, something must
be
> wrong with your timeouts.
Thanks - I hadn''t actually tried the power saving and screensaver
stuff,
but it turned out not to help. When the screensaver starts up, the mouse 
just makes the screen go blank again. Oddly, the screensaver seems to 
start up after a fixed delay of about 8 minutes, whatever the 
screensaver delay is set to. It''s also not the image in the screensaver
settings.
> Xinetd implies your vnc server is on the domu, instead of the dom0. Have
you
> tried the vnc server built into qemu-dm? (vncviewer localhost:port#)
Yes, I have the server on my DomU''s - I haven''t actually tried
the qemu
one. I''ve got another 4 (RedHat) DomU''s where this all worked
with no
problems.
>> DISPLAYMANAGER_SHUTDOWN="root"
> 
> You realize this refers to xdmcp, not vnc, right?
Yes - very confusing. All the stuff I read about about getting VNC going 
on suse basically just  says that you have to enable remote management 
in yast, without saying why, or what it does. As far as I can make out, 
it mainly changes some bits in gdm.conf to do with xdmcp so, as you say, 
  it doesn''t seem to be relevant.
> My experience with chooser boxes is that they may not see all available
hosts
> on a scan, but if you type in the hostname, you can connect. 
Interesting - I did a direct connection without using the chooser and 
did connect without a problem. The remote X server still has exactly the 
same problem as the remote VNC client though: the screen just blanks 
after the login.

Thanks -

Evan

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On Sunday 27 January 2008 03:51:58 pm Evan Lavelle
wrote:
> Some progress - I can connect over anything (xdmcp, vnc, sdl) if I logon
> as root, but not otherwise. However, it can''t be an authentication
> problem, since I get well beyond the login screen if I log in as myself.
> The display doesn''t blank until just before it creates the panel
at the
> bottom. I suspect it may be something to do with the gdm PreSession
> scripts, but I can''t see any obvious problems.
Then I would suggest another basic check: on domu, do "ls -alFR
$HOME|less",
and search for ''root'' ownership of any file that
shouldn''t be root, and chown
it back to $USER:users.

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On Sunday 27 January 2008 18:11:57 Evan Lavelle wrote:
> I''ve just uneventfully installed SLES10 as an HVM DomU (after
finding
> out, the hard way, that OpenSUSE 10.3 won''t install on Intel VT).
Echoing some of Jim''s comments too. openSUSE 10.3 absolutely installs
on
Intel-VT and AMD-V hardware. It''s not mentioned anywhere, but what is 
the Dom0? (I would guess SLES 10?)
> This almost went without a hitch, but I''ve been banging my head
> against a brick wall for a few hours trying to get VNC working. I can
> get a remote desktop, but a few seconds after I log in to the remote
> desktop, the screen goes blank (just after I get the "Suse linux
> enterprise 10" screen). Bizarrely, the SLES10 screen saver *does*
> appear on the remote desktop a few minutes later. Another odd thing
> is that the SDL window on my Dom0 has exactly the same behaviour:
> when I log in on the remote vnc client, I get some startup activity
> on the SDL window for a few seconds, and then it goes blank. The
> screensaver starts on the SDL window at the same time as on the vnc
> client. The only way I can talk to the DomU is on ssh.
When I first read this I thought you were trying to set up remote access 
to Dom0, but after a few subsequent reads it seems as though you want 
access via VNC to a DomU? A couple of questions:
1. Assuming SLES 10 is your Dom0, are you patched up to date, 
particularly with SP1? Generally, HVM installations with SP1 by default 
use a VNC session rather than SDL for viewing the DomU on Dom0.
2. Why are you using HVM for this instance rather than 
paravirtualisation?
> Any ideas? I''m pretty sure that the vnc setup is correct on the
DomU.
> I''ve enabled it via ''remote administration'' on
YaST, xinetd is
> running, I can mod /etc/xinetd.d/vnc, etc (and I can log in anyway,
> so it must basically be working).
As Jim has mentioned previously, have you thought about using the 
qemu-vnc session itself? This is run on the Dom0 and is what 
virt-manager uses to connect to the DomU. I would suspect that a remote 
VNC connection to DomU should work without having to jump through all 
these hoops.
> I''m using a realVNC client, but SLES appears to use tightVNC. I
don''t
> think this is a problem. I can start a local tightVNC viewer on the
> DomU (with ssh -X), and it has exactly the same behaviour as the
> remote one (though possibly without the screensaver).
The different VNC packages won''t matter - VNC is VNC... I know KDE has
a
desktop sharing option that allows you to temporarily share your 
desktop with another user via VNC. It would be interesting to see if 
this works. Do any of the usual logs (/var/log/messages etc.) provide 
any insights into what is going on?
> Another potential issue is that the relevant stuff on Google
> generally talks about using xdm, but SLES10 uses gdm by default,
> although I can''t see how this could be relevant.
>
> Any thoughts? /etc/sysconfig/displaymanager currently contains
(I''ve
> tried some variants):
>
> DISPLAYMANAGER="gdm"
> DISPLAYMANAGER_REMOTE_ACCESS="yes"
> DISPLAYMANAGER_ROOT_LOGIN_REMOTE="yes"
> DISPLAYMANAGER_STARTS_XSERVER="yes"
> DISPLAYMANAGER_XSERVER_TCP_PORT_6000_OPEN="yes"
> DISPLAYMANAGER_AUTOLOGIN="evan"
> DISPLAYMANAGER_PASSWORD_LESS_LOGIN="no"
> DISPLAYMANAGER_AD_INTEGRATION="no"
> DISPLAYMANAGER_SHUTDOWN="root"
Again, echoing Jim, this is all related to XDMCP rather than VNC. I 
guess you''re just trying to get a remote login of any sort set up, 
hence it''s inclusion here?

Just to satisfy my own curiousity - why is X forwarding via ssh not a 
viable solution for you?

Jon

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Jonathan Ervine wrote:
> On Sunday 27 January 2008 18:11:57 Evan Lavelle wrote:
>> I''ve just uneventfully installed SLES10 as an HVM DomU (after
finding
>> out, the hard way, that OpenSUSE 10.3 won''t install on Intel
VT).
> 
> Echoing some of Jim''s comments too. openSUSE 10.3 absolutely
installs on
> Intel-VT and AMD-V hardware. It''s not mentioned anywhere, but what
is
> the Dom0? (I would guess SLES 10?)
The main issue is getting out of the graphical installer; apparently the 
text installer works. You can, in principle, do this with the shift key, 
but it''s next to impossible in practice. See Ian Jackson''s
post on
xen-devel 
(http://lists.xensource.com/archives/html/xen-devel/2007-12/msg00564.html) 
for various other problems. Ian doesn''t say *why* it''s
necessary to turn
off gfxboot; see the other post 
(http://www.mail-archive.com/fedora-xen@redhat.com/msg00699.html) for 
details. My own fix was much simpler - install SLES 10 instead  :)

Dom0 is Fedora 8, Xen 3.1, so I haven''t addressed your other points 
concerning SLES 10 Dom0''s. The issue of looking at DomU''s on a
dom0 via
qemu is interesting, but it doesn''t fit in with the way I do things.
The
Dom0 is practically irrelevant - it''s headless, and only exists to 
create and shutdown DomU''s. I imagine that this is a common way to use 
Xen. Each DomU runs a vnc server, with a remote client somewhere else on 
the network.
> 2. Why are you using HVM for this instance rather than 
> paravirtualisation?
It''s easier (ha). This box has 7 DomU''s, Linux&Windows,
all HVM, and all
worked out of the box, except OpenSUSE and SLES 10. I can live with the 
lower performance, and I''ve had a lot of trouble with PV
domU''s on F8.
> I know KDE has a 
> desktop sharing option that allows you to temporarily share your 
> desktop with another user via VNC. It would be interesting to see if 
> this works. Do any of the usual logs (/var/log/messages etc.) provide 
> any insights into what is going on?
I only installed Gnome. Nothing in the log files, unfortunately. The 
relevant stuff looks like it should go to .xsession-errors, but that 
always contains lots of incomprehensible stuff anyway.
> Just to satisfy my own curiousity - why is X forwarding via ssh not a 
> viable solution for you?
To some extent, perhaps bloody-mindedness. It works on everything else. 
I took a break from this yesterday and installed a complete WinXP DomU, 
with a remote vnc login, in ~90 minutes, without a hitch. Besides, I 
normally use Windoze as a front-end, so that brings up all sorts of 
problems to do with Cygwin/ssh/X installation.

BTW - something I forgot to mention in my last post - I can log in from 
anything, without being root, if I use a failsafe Gnome session. I''ve 
just had a quick look on Google for this, and found at least one hit for 
someone who had the same problem after installing SP1 for SLES10, so 
I''ll chase that up.

- Evan

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Sorry - nothing to do with Xen, or even vnc.

SLES10/SP1 won''t let you do a graphical login if your shell is tcsh. I 
could login as root because root uses bash, but not as myself. The 
problem is probably somewhere in /etc/X11/xdm/Xsession, but I can''t be 
bothered to look for it.

Clearly, there''s some disagreement between myself and Novell about what
the word ''Enterprise'' means.

- Evan

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Saw that you tracked down the problem to tcsh. Just some follow up comments:

On Monday 28 January 2008 05:20:20 am Evan Lavelle
wrote:
> Dom0 is Fedora 8, Xen 3.1, so I haven''t addressed your other
points
> concerning SLES 10 Dom0''s. The issue of looking at DomU''s
on a dom0 via
> qemu is interesting, but it doesn''t fit in with the way I do
things. The
> Dom0 is practically irrelevant - it''s headless, and only exists to
> create and shutdown DomU''s. I imagine that this is a common way to
use
> Xen. Each DomU runs a vnc server, with a remote client somewhere else on
> the network.
The server being headless doesn''t stop qemu-dm from serving a vnc
session on
dom0, for windows or linux. Less work for you installing a vnc server in your 
domu, since it is already setup. I suppose this is just the way you are used 
to working.
>> 2. Why are you using HVM for this instance rather than 
>> paravirtualisation?
> It''s easier (ha). This box has 7 DomU''s,
Linux&Windows, all HVM, and all
> worked out of the box, except OpenSUSE and SLES 10. I can live with the 
> lower performance, and I''ve had a lot of trouble with PV
domU''s on F8.
Actually, It might well be easier come upgrade time to the next SuSE version, 
since you can use the install dvd, instead of ''yum update'' or
Yast2. (You
have to redefine your repository/sources definitions, and probably manually 
download and install ''openSUSE-release'' to get things started.
I had to do
something similar going from fedora fc7 -> fc8.)
>> I know KDE has a 
>> desktop sharing option that allows you to temporarily share your 
>> desktop with another user via VNC. It would be interesting to see if 
>> this works. Do any of the usual logs (/var/log/messages etc.) provide 
>> any insights into what is going on?
> I only installed Gnome.
Gnome has ''vino'' which does the same thing.

Glad it is working for you now.

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jim burns wrote:
> 
> Saw that you tracked down the problem to tcsh. Just some follow up
> comments:
> 
> On Monday 28 January 2008 05:20:20 am Evan Lavelle wrote:
>> Dom0 is Fedora 8, Xen 3.1, so I haven''t addressed your other
points
>> concerning SLES 10 Dom0''s. The issue of looking at
DomU''s on a dom0 via
>> qemu is interesting, but it doesn''t fit in with the way I do
things. The
>> Dom0 is practically irrelevant - it''s headless, and only
exists to
>> create and shutdown DomU''s. I imagine that this is a common
way to use
>> Xen. Each DomU runs a vnc server, with a remote client somewhere else
on
>> the network.
> 
> The server being headless doesn''t stop qemu-dm from serving a vnc
session
> on 
> dom0, for windows or linux. Less work for you installing a vnc server in
> your 
> domu, since it is already setup. I suppose this is just the way you are
> used 
> to working.
> 
>>> 2. Why are you using HVM for this instance rather than 
>>> paravirtualisation?
> 
>> It''s easier (ha). This box has 7 DomU''s,
Linux&Windows, all HVM, and all
>> worked out of the box, except OpenSUSE and SLES 10. I can live with the
>> lower performance, and I''ve had a lot of trouble with PV
domU''s on F8.
> 
> Actually, It might well be easier come upgrade time to the next SuSE
> version, 
> since you can use the install dvd, instead of ''yum
update'' or Yast2. (You
> have to redefine your repository/sources definitions, and probably
> manually 
> download and install ''openSUSE-release'' to get things
started. I had to do
> something similar going from fedora fc7 -> fc8.)
> 
>>> I know KDE has a 
>>> desktop sharing option that allows you to temporarily share your 
>>> desktop with another user via VNC. It would be interesting to see
if
>>> this works. Do any of the usual logs (/var/log/messages etc.)
provide
>>> any insights into what is going on?
> 
>> I only installed Gnome.
> 
> Gnome has ''vino'' which does the same thing.
> 
> Glad it is working for you now.
> 
> _______________________________________________
> Xen-users mailing list
> Xen-users@lists.xensource.com
> http://lists.xensource.com/xen-users
> 
> 

FYI.  I was able to resolve the remote login blank screen problem by adding
/usr/X11R6/bin and /opt/gnome/bin to my path in my .cshrc file.
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