Regarding rosdep

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rosdep install sets up some files that rosdep isn't able to install when you install rosdep. You only need to do this once, when you install rosdep.

rosdep update updates the dependency database for resolving generic system package names to packages for your operating system.

The only times when you need to do this are during the initial installation (to initialize the database), and before you run rosdep install, to make sure that you have the most recent database before installing system packages.

The rosdep database doesn't change often, so running rosdep update more than once a day probably won't help unless you know that there has been a database change since the last time you ran it.