Solving a few issues with the CORE Network Emulator running on Xubuntu Linux

March 22, 2014

When I started a CORE Network Emulator simulation scenario on my computer running the Xubuntu Linux 13.10 operating system, I encountered a few issues that I needed to correct.

The Ubuntu Network Manager drops my WiFi connection after I start the CORE simulation scenario and the Terminal does not start when I double-click on a node in the CORE canvas.

This post describes how I worked around the WiFi connection problem and resolved the Terminal problem.

Ubuntu Network Manager problem workaround

UPDATE May 20, 2014: We found a permanent fix for this problem. See the sections referring to NetworkManager in the post about eliminating garbage data in the CORE network simulator.

As soon as the CORE simulation scenario starts, the computer’s WiFi network connection fails. This does not impact the operation of the CORE Network Emulator, but it is an inconvenience for anyone using the host computer.

In the Ubuntu Network Manager, disconnect, then reconnect WiFi network to restore host's WLAN connection

In the Ubuntu Network Manager, disconnect, then reconnect WiFi network to restore host’s WLAN connection

It seems that the Ubuntu Network Manager application has some compatibility issues when LXC containers are started on the host system1.

Each virtual ethernet interface created by CORE appears as a “wired connection” Ethernet interface to the Network Manager application, which then drops my current WiFi or LAN connection and tries to connect to the new virtual ethernet links. The same problem also occurs if the host computer is directly connected to an Ethernet cable. Solving this issue will take some research time (and would be a subject for another post).

Fortunately there is a workaround: manually “disconnect” and then “reconnect” the computer’s WiFi (or Ethernet LAN) connection in Network Manager. You must do this every time you start or re-start a CORE simulation scenario.

To disconnect and reconnect the WiFi interface, click on the Network manager icon in the status bar and then click on “Disconnect” below the WiFi interface. Then, after the WiFi interface completes disconnecting, click on the Network manager icon and click on “Connect” below the WiFi interface.

Other Linux distributions that do not use Network Manager may not have this problem.

Terminal application problem solved

When I double-click on a virtual node in the CORE canvas, I expect that a Terminal window will open up that is connected to a bash shell running on the virtual node. But, the Terminal window does not open.

In the console window (the terminal from which I started the CORE GUI), I see the error message: xfce4-terminal: Unknown option "-c".

It seems CORE is using the wrong startup option when it launches the XFCE Terminal application. To fix this problem, follow these steps:

  1. Open the CORE Preferences panel using the menu command:

    Edit → Preferences
  2. For the Terminal program, select the xfce-terminal -e option.
    core network emulator preferences panel
  3. Then, change the text in the option field from “-e” to “-x”. The “-x” option will correctly execute the command string that CORE passes to the terminal app to set the name of the node in the terminal banner.
    core network emulator preferences panel


We successfully resolved some of the issues that occurred when running the CORE Network Emulator 4.6 in Xubuntu Linux 13.10. The same issues might or might not occur in other distributions.

  1. This may be the same problem that is mentioned in the bug report: 

2 responses to Solving a few issues with the CORE Network Emulator running on Xubuntu Linux

  1. Thanks a lot for sharing!
    I was just facing the same issue (terminal)!

Trackbacks and Pingbacks:

  1. Eliminate garbage data in the CORE Network Emulator | Open-Source Routing and Network Simulation - May 12, 2014

    […] problems in some situations. For example, we have previously seen how the CORE Network Emulator can temporarily interrupt the host system’s WiFi network connection when a simulation is started because NetworkManager tries to switch to the newly-created virtual […]