When configuring ROS distributed / Error report solution and command requirements encountered in the process of master-slave computer

    Error: SSH: connect to host * * port 22: network is unreachable
    cause: network is disconnected
    solution: restart virtual machine or manually connect or command to restart network connection

    sudo service network-manager restart

      Error: Unit network.service Not found.
      reason: wrong command

        Error: ROS error: the window cannot be opened remotely qxcbconnection: could not connect to display
        qxcbconnection: could not connect to display
        reason: the graphical window cannot be opened remotely

          Error: under Ubuntu 16.04, the terminal input sudo The problem of sudo: unable to resolve host Ubuntu: connection timed out occurs
          cause: this problem is caused by the inconsistency between the host name (localhost) in hosts and the host name in the “etc” folder of the system disk.
          Solution: set hosts to be consistent

            Requirements: view the SSH connection of Linux
            command:

            ps aux | grep sshd

              Requirements: use the service command to start the SSH service. The command execution is as follows.
              Command:

              service sshd start

                Requirement: how to view the Pi of the host connected through SSH in Ubuntu
                command:

                who

                  Requirements: how to modify user password in Ubuntu
                  command:

                  usrname@usrname-laptoppasswd:~$passwd usrname