TurboVNC over SSH

[rgu...@gmail.com]

Hi Folks,

I have been using TurboVNC through an SSH tunnel on Windows. However, when my clients connect they receive a confirmation window because the host key is unknown. Since my environment is controlled, I would like to skip this warning message and just connect (something similar to ssh -o StrictHostKeyChecking=no -o UserKnownHostsFile=/dev/null user@host). 

I have tried to use both cvncviewer.exe and VncViewer.jar for this, but with no success.

In both cases, I created a .bat file with the following content:

@echo off

SET VNC_VIA_CMD=ssh.exe  -o StrictHostKeyChecking=no -o UserKnownHostsFile=/dev/null -f -L %L:%H:%R %G sleep 20

java -jar VncViewer.jar -via server.domain -sshport 5900 -vncpasswd vncfile -ExtSSH localhost

I have also tried this other way, but with no luck...

@echo off

java -Dturbovnc.via="ssh.exe  -o StrictHostKeyChecking=no -o UserKnownHostsFile=/dev/null -f -L %L:%H:%R %G sleep 20" -jar VncViewer.jar -via server.domain -sshport 5900 -vncpasswd vncfile -ExtSSH localhost

What am I doing wrong?

Cheers,

Rafael

[DRC]

Several comments/questions:

- Generally speaking, you should not execute VncViewer.jar directly. You
should use the vncviewer-java.bat (console) or vncviewer-javaw.bat (no
console) batch scripts, which will properly load the TurboVNC Helper.
That isn't the cause of this issue, but running the TurboVNC Viewer
without the TurboVNC Helper will result in a loss of functionality. To
pass Java system properties to the Java TurboVNC Viewer, set them in the
JAVA_TOOL_OPTIONS environment variable (e.g. 'set
JAVA_TOOL_OPTIONS=-Dturbovnc.foo=bar'.)

- Are you sure that 5900 is the correct SSH port? 5900 is generally a
port on which a VNC server listens, not a port on which an SSH server
listens. That could be the source of the error. The default value of
SSHPort is 22, which is correct for most SSH servers.

- When setting VNC_VIA_CMD in a .bat file, you have to escape the %
symbols, so your .bat file should look something like this:

@echo off
setlocal
set VNC_VIA_CMD=ssh.exe -o StrictHostKeyChecking=no -o
UserKnownHostsFile=/dev/null -f -L %%L:%%H:%%R %%G sleep 20
"c:\program files\turbovnc\cvncviewer.exe" -via {server}.{domain}
{other_TurboVNC_Viewer_args} localhost:{display_number}

That could be the source of the error.

- Neither viewer (Java nor native) accepts an argument of -vncpasswd.
That could be the source of the error. The Java TurboVNC Viewer accepts
-passwd, which seems to be what you're aiming for. The native Windows
TurboVNC Viewer does not have a mechanism for reading a VNC password
file directly.

- I presume that ssh.exe is a Cygwin-derived implementation of OpenSSH,
but if it isn't, then please note that only Cygwin-derived
implementations of OpenSSH can be used on Windows with the native
Windows TurboVNC Viewer or the Java TurboVNC Viewer with -extssh.
Native Windows implementations of OpenSSH, including the Microsoft
implementation in Windows 10 and the MSYS implementation, do not
properly support the SSH fork option (-f).

- In general, -extssh is not very well supported in the Windows/Java
TurboVNC Viewer. It won't work at all if any interactive input (such as
an SSH password or SSH public key passphrase) is required. Thus, I
would recommend using the native Windows TurboVNC Viewer (cvncviewer),
which would mean that you need to find another way to read the VNC
password file and pass it to that viewer.

- If you are connecting to the TurboVNC Server or another Un*x Xvnc
server, then you need to specify the display number. Otherwise, the
TurboVNC Viewer will connect to display :0 by default, which is probably
not what you want. That could be the source of the error.

If none of those is the source of the error, then please tell me what
the error actually is. "No success" doesn't tell me anything useful.

DRC

On 3/17/20 7:54 AM, rgu...@gmail.com wrote:
> Hi Folks,
>
> I have been using TurboVNC through an SSH tunnel on Windows. However,
> when my clients connect they receive a confirmation window because the
> host key is unknown. Since my environment is controlled, I would like to
> skip this warning message and just connect (something similar to ssh -o
> StrictHostKeyChecking=no -o UserKnownHostsFile=/dev/null user@host). 
>
> I have tried to use both cvncviewer.exe and VncViewer.jar for this, but
> with no success.
>
> In both cases, I created a .bat file with the following content:
>

> /@echo off/
> /SET VNC_VIA_CMD=ssh.exe  -o StrictHostKeyChecking=no -o
> UserKnownHostsFile=/dev/null -f -L %L:%H:%R %G sleep 20/
> /java -jar VncViewer.jar -via server.domain -sshport 5900 -vncpasswd
> vncfile -ExtSSH localhost/

>
> I have also tried this other way, but with no luck...
>

> /@echo off/
> /java //-Dturbovnc.via="ssh.exe  -o StrictHostKeyChecking=no -o
> UserKnownHostsFile=/dev/null -f -L %L:%H:%R %G sleep 20" //-jar

> VncViewer.jar -via server.domain -sshport 5900 -vncpasswd vncfile

> -ExtSSH localhost/

[DRC]

A couple of updates/corrections:

- The SSH implementation in MSYS2 does in fact work with the TurboVNC
viewers (my bad.  I forgot I had tested that.)

- I fixed the ExtSSH implementation in the Java TurboVNC Viewer, so it
now properly redirects input and output from the SSH subprocess.  Thus,
'-via -extssh' in the Windows/Java TurboVNC Viewer should now work
identically to '-via' in the native Windows TurboVNC Viewer.  That fix
is available in the latest 2.2.x stable pre-release build
(https://turbovnc.org/DeveloperInfo/PreReleases) once Travis finishes
spinning it.

Let me know if you have any further problems or need additional help.