Lawrence Livermore National Laboratory



15. Why can't I connect to a remote computer?

Sometimes VisIt fails to connect to a remote computer while trying to access files in distributed mode. This can happen for a variety of reasons and they are usually related to how your computer is configured to access the network. First of all, VisIt uses SSH to launch its components on remote computers and it is possible that SSH was unable to launch VisIt on the remote computer. If you want to verify this, run visit -debug 5and then check to see if any vcl, mdserver, or engine log files are present on the remote computer in your home directory. If no log files were created then SSH was probably not able to launch VisIt components on the remote computer. In that case, make sure that you can SSH to the remote computer. Also check your local VisIt installation's Host profiles to make sure the path to VisIt on the remote computer is specified. Alternatively, you can set the PATH environment variable on the remote computer so it contains the path to the program visit.

If there were no debug logs to be found on the remote computer and your local computer runs a newer version of Linux then quit VisIt and try running visit -nopty -debug 5. The -nopty option tells VisIt not to allocate a pseudoterminal in which to run SSH. When you run with the -nopty option, VisIt's password window will not be used. Instead, look for an SSH prompt in the terminal window where you ran VisIt. You should be able to enter your password at that prompt. If successful, SSH should continue trying to launch VisIt on the remote computer. If VisIt still cannot connect after SSH launches VisIt's remote components, check for debug logs on the remote computer to see if VisIt was at least able to launch there.

If you found debug log files on the remote computer but VisIt still can't connect then it's possible that the remote computer cannot connect back to your local computer. This is caused either by a networking problem or a firewall that is disallowing inbound network connections to your local computer. The simplest solution is to use SSH tunneling. If that doesn't correct the problem then you will need to correct the networking and/or firewall issues.

Enabling SSH Tunneling

SSH tunneling is enabled by going to the Options pulldown menu at the top of them main window and bringing up the Host profiles window, selecting the profile for the remote computer, selecting the Advanced options tab, selecting the Networking tab, toggling the Tunnel data connections through SSH setting, and pressing the Apply button.

Correcting Networking Issues

Some desktop computers do not provide a valid network name when VisIt asks for one. If you suspect that this could be the cause of the launch failure, try using Parse from SSH_CLIENT in your host profile for the remote computer. If that does not work and if you are using VPN then you should try manually setting the local host name VisIt will use when telling its remote components to connect back to your local computer. Open the Host profiles window and go to the Advanced options tab. Click the Specify manually radio button and type in the IP address of your VPN session into the adjacent text field before you try connecting again.

Correcting Firewall Issues

VisIt uses ports 5600-5609 to listen for incoming connections (when they are expected) from remote VisIt components. If you've tried the previous suggestions and none of them worked then you may have a firewall denying VisIt access to your local computer. Try turning the firewall off or allowing ports 5600-5609 and run VisIt again. If you do not know how to enable ports for your firewall or if you do not have the required privileges, contact your system administrator.

If none of these suggestions allow you to successfully connect to the remote computer then contact visit-users@ornl.gov and provide information about how you are trying to connect. Be sure to include the VisIt version and platform on which you are running in your e-mail.