安裝turtlebot3 ros2 dashing的時候，遇到要安裝gazebo的問題：
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GAZEBO INSTALLATION SCRIPT
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This script is installing the latest stable version of
Gazebo Simulator available from your package manager
Warning: the "gazebo" command appears to already exist on this system.
If you already have gazebo installed, this script can cause trouble, which is
why we're displaying this warning and provide the opportunity to cancel the
installation.
If you installed the current gazebo package using this script and are using it
again to update gazebo, you can safely ignore this message.
You may press Ctrl+C now to abort this script.
+ sleep 20
In Debian this script will setup the osrfoundation
repository to install the latest package available
+ sudo -E sh -c apt-key adv --keyserver keyserver.ubuntu.com --recv-keys D2486D2DD83DB69272AFE98867170598AF249743
Executing: /tmp/apt-key-gpgho