Troubleshooting

Connection

roslaunch is not working

You may see errors like the following:

• error launching XXX: No such file or directory

This and other similar errors are due to ROS being extremely picky about networking. The following must be true:

• On your machine:
  • Your hostname must match the name other machines use on the network. I.e. if your machine is called student001 then typing ping student001 on the Q.bo must reach your machine.
  • The ROS_HOSTNAME environment variable must be set to that hostname.
  • The ROS_MASTER_URI environment variable must be set to, in this case, http://student001:11311. Replace student001 as appropriate.
  • The command ssh qbo@binky must log you into the Q.bo without a password. Use the ssh-copy-id program.
• On the Q.bo:
  • Your hostname must be contactable by the Q.bo. I.e. the command ping student001 must work replacing your hostname as appropriate.

NOTE: When we use 'hostname', we mean 'hostname'. I.e. student001, not student001.eng.cam.ac.uk which is a fully qualified name.

XXX is not in your SSH known_hosts file

This is because the version of SSH shipped with ROS cannot understand the ~/.ssh/known_hosts generated by the latest SSH. Assuming the Q.bo's IP address is 129.169.154.82, firstly remove the existing entry:

$ ssh-keygen -f "/home/rjw57/.ssh/known_hosts" -R 129.169.154.82

Then log in again forcing the use of the RSA algorithm:

$ ssh -oHostKeyAlgorithms='ssh-rsa' 129.169.154.82

See a related ROS forum answer.