MD5sum error: Client [/rostopic...] wants topic /move_group/display_planned_path to have datatype/md5sum [moveit_msgs/DisplayTrajectory/c3c039...], but our version has [moveit_msgs/DisplayTrajectory/41936...]

asked 2020-07-31 08:41:10 -0500

thejose gravatar image

I am running the Moveit! tutorial demo.launch file from panda_moveit_config. After running this launch file, when I try to echo the contents of any /move_group/.... topic, I receive the following error:

[ERROR] [1596202093.852304142]: Client [/rostopic_11410_1596202092781] wants topic /move_group/display_planned_path to have datatype/md5sum [moveit_msgs/DisplayTrajectory/c3c039261ab9e8a11457dac56b6316c8], but our version has [moveit_msgs/DisplayTrajectory/41936b74e168ba754279ae683ce3f121]. Dropping connection.

This was working perfectly some time ago while I was running the Move Group C++ Interface Tutorial and suddenly stopped working. I would be very grateful if someone could help me figure this out.

I need to access these topics (more specifically move_group/display_planned_path) in order to find the joint velocity for a particular joint in a path planned by moveit. Any workarounds to achieve this will also be much appreciated.

Setup:

Ubuntu 18

ROS Melodic

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Comments

1

Hi @thejose.

This particular error is telling you that the version (md5) of moveit_msgs/DisplayTrajectory msg is different between nodes. In particular it is saying you that the version used in the node is different from the one ROS has.

So you need to make sure you've compiled your workspace with the same version of the msg. One thing that can be happening is that the message definition has changed and you still have old compiled versions in you devel and build folders of your workspace. Try to delete those, compile again your workspace and see if the error persists.

Weasfas gravatar image Weasfas  ( 2020-08-01 06:06:12 -0500 )edit

Hi @Weasfas, thank you for your comment. I looked into the DisplayTrajectory.h file. There are 2 copies of this, 1 in my workspace/devel/include and the other in my opt/ros/melodic/include. Both of these copies have different md5sums defined in them. Do you think it is a good idea to manually change the md5sum in one of the files to be the same as the other? Also, do you have any clue as to how this difference might have occurred?

Edit: I changed the md5sum in one of the files to be the same as the other and it worked perfectly! Thank you so much. However, I am still a little worried that this change may affect other packages.

thejose gravatar image thejose  ( 2020-08-01 08:41:59 -0500 )edit

I changed the md5sum in one of the files to be the same as the other and it worked perfectly!

Don't ever do this.

That hash is there for a reason, and it's not to be changed by users.

gvdhoorn gravatar image gvdhoorn  ( 2020-08-01 10:00:01 -0500 )edit

Oh Okay. Do you have a suggestion on what else I could do to fix this problem?

thejose gravatar image thejose  ( 2020-08-01 10:17:40 -0500 )edit
1

@thejose, If it is true what you said it seems to me that you have compiled a message which you already installed in your OS (with apt maybe), so the solution would be to use only one of them. Either you unistall that package and use only the compile version of your workspace or just do not compile it and use the one that is in ROS path.

Weasfas gravatar image Weasfas  ( 2020-08-02 06:18:19 -0500 )edit