RViz segfaults unless a monitor is connected, any way to prevent this?

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What you are likely seeing is that, without the VGA connected, your graphics doesn't startup at all. On our robots, without a monitor plugged in on bootup, the discrete graphics cards don't get initialized and X never starts, so VNC with RViz wouldn't work so well.

In either case, VNC or forwarding X is probably not the best way to work with rviz remotely. A much better plan would be to follow the directions on NetworkSetup to get your computer connected to the robot's rosmaster (setting the ROS_MASTER_URI and ROS_IP for both machines is what I do instead of setting up DNS). This way, you can run rviz locally on your computer, only sending ROS data across the network instead of forwarding X or VNC, both of which I found to be quite slow when working with a 3D application like rviz.

Try virtualgl. It did solve the rviz segfault for me. When your finished setting up just run rviz like this:

vglrun rosrun rviz rviz

http://en.wikipedia.org/wiki/Xvfb is something what helped me on case when I needed dummy graphics.

Load it up under gdb and run a backtrace to see what the root cause is. I'd guess that it's probably the graphics drivers causing the segfault, there are a number of Rviz segfaults that go away when using better/newer graphics drivers.

A dummy driver can help!

Just following the first voted answer here https://askubuntu.com/questions/453109/add-fake-display-when-no-monitor-is-plugged-in.

It works for me in Ubuntu 16.04 with a little modification:

• Replace the installation with sudo apt install xserver-xorg-video-dummy-lts-xenial.
• And write in the configuration file /usr/share/X11/xorg.conf.d/xorg.conf following the above link.

Section "Device"
    Identifier  "Configured Video Device"
    Driver      "dummy" EndSection

Section "Monitor"
    Identifier  "Configured Monitor"
    HorizSync 31.5-48.5
    VertRefresh 50-70 EndSection

Section "Screen"
    Identifier  "Default Screen"
    Monitor     "Configured Monitor"
    Device      "Configured Video Device"
    DefaultDepth 24
    SubSection "Display"
    Depth 24
    Modes "1024x800"
    EndSubSection EndSection

• Reboot, and now RViz can work over VNC without monitor.

Another thing - monitors do use I2C for identification purposes. They use 0x37 and some other address. Maybe you need to set up some dummy i2c client. More info is here http://www.paintyourdragon.com/?p=43