Troubleshooting and tricks

Connection problems

  • When AiiDA tries to connect to the remote computer, it says paramiko.SSHException: Server u'FULLHOSTNAME' not found in known_hosts

    AiiDA uses the paramiko library to establish SSH connections. paramiko is able to read the remote host keys from the ~/.ssh/known_hosts of the user under which the AiiDA daemon is running. You therefore have to make sure that the key of the remote host is stored in the file.

    • As a first check, login as the user under which the AiiDA daemon is running and run a:


      command, where FULLHOSTNAME is the complete host name of the remote computer configured in AiiDA. If the key of the remote host is not in the known_hosts file, SSH will ask confirmation and then add it to the file.

    • If the above point is not sufficient, check the format of the remote host key. On some machines (we know that this issue happens at least on recent Ubuntu distributions) the default format is not RSA but ECDSA. However, paramiko is still not able to read keys written in this format.

      To discover the format, run the following command:

      ssh-keygen -F FULLHOSTNAME

      that will print the remote host key. If the output contains the string ecdsa-sha2-nistp256, then paramiko will not be able to use this key (see below for a solution). If instead ssh-rsa, the key should be OK and paramiko will be able to use it.

      In case your key is in ecdsa format, you have to first delete the key by using the command:

      ssh-keygen -R FULLHOSTNAME

      Then, in your ~/.ssh/config file (create it if it does not exist) add the following lines:

      Host *
        HostKeyAlgorithms ssh-rsa

      (use the same indentation, and leave an empty line before and one after). This will set the RSA algorithm as the default one for all remote hosts. In case, you can set the HostKeyAlgorithms attribute only to the relevant computers (use man ssh_config for more information).

      Then, run a:


      command. SSH will ask confirmation and then add it to the file, but this time it should use the ssh-rsa format (it will say so in the prompt messsage). You can also double-check that the host key was correctly inserted using the ssh-keygen -F FULLHOSTNAME command as described above. Now, the error messsage should not appear anymore.