1、问题 按照官网一步一步来看似很顺利，但当走到最后一步时：
$ sudo rosdep init $ rosdep update在进行sudo rosdep init 时出现了意想不到的问题：
ERROR: cannot download default sources list from: https://raw.githubusercontent.com/ros/rosdistro/master/rosdep/sources.list.d/20-default.list Website may be down.小作很苦恼，但将连接复制到浏览器里时却发现浏览器也打不开该网页，说明是由于网站为国外网站所导致的。 在网上搜到对我自己最有效的解决办法现记录如下： 在通过某种手段打开上述连接后发现为一个文件，但是下载不到，那么就通过本地创建的方法建立。 （1）在本地创建目录/etc/ros/rosdep/sources.list.d，并进入
/etc/ros/rosdep/sources.list.d $ cd /etc/ros/rosdep/sources.list.d（2）自己创建一个20-default.list，并进行编辑
sudo gedit 20-default.list并将网页中的内容复制粘贴
# os-specific listings first yaml https://raw.githubusercontent.com/ros/rosdistro/master/rosdep/osx-homebrew.yaml osx # generic yaml https://raw.githubusercontent.com/ros/rosdistro/master/rosdep/base.yaml yaml https://raw.githubusercontent.com/ros/rosdistro/master/rosdep/python.yaml yaml https://raw.githubusercontent.com/ros/rosdistro/master/rosdep/ruby.yaml gbpdistro https://raw.githubusercontent.com/ros/rosdistro/master/releases/fuerte.yaml fuerte # newer distributions (Groovy, Hydro, ...) must not be listed anymore, they are being fetched from the rosdistro index.yaml instead并将其中所有的raw.githubusercontent.com改为raw.github.com,则得到最终的20-default.list，如下：
# os-specific listings first yaml https://raw.github.com/ros/rosdistro/master/rosdep/osx-homebrew.yaml osx # generic yaml https://raw.github.com/ros/rosdistro/master/rosdep/base.yaml yaml https://raw.github.com/ros/rosdistro/master/rosdep/python.yaml yaml https://raw.github.com/ros/rosdistro/master/rosdep/ruby.yaml gbpdistro https://raw.github.com/ros/rosdistro/master/releases/fuerte.yaml fuerte # newer distributions (Groovy, Hydro, ...) must not be listed anymore, they are being fetched from the rosdistro index.yaml instead（3）在终端直接运行
rosdep update得到以下信息便成功！
reading in sources list data from /etc/ros/rosdep/sources.list.d Hit https://raw.github.com/ros/rosdistro/master/rosdep/osx-homebrew.yaml Hit https://raw.github.com/ros/rosdistro/master/rosdep/base.yaml Hit https://raw.github.com/ros/rosdistro/master/rosdep/python.yaml Hit https://raw.github.com/ros/rosdistro/master/rosdep/ruby.yaml Hit https://raw.github.com/ros/rosdistro/master/releases/fuerte.yaml Query rosdistro index https://raw.githubusercontent.com/ros/rosdistro/master/index-v4.yaml Skip end-of-life distro "ardent" Skip end-of-life distro "bouncy" Skip end-of-life distro "crystal" Add distro "dashing" Add distro "eloquent" Add distro "foxy" Skip end-of-life distro "groovy" Skip end-of-life distro "hydro" Skip end-of-life distro "indigo" Skip end-of-life distro "jade" Add distro "kinetic" Skip end-of-life distro "lunar" Add distro "melodic" Add distro "noetic" Add distro "rolling" updated cache in /home/userName/.ros/rosdep/sources.cache该方法就是将网页中的文件人为放置到本地位置！！代替sudo rosdep init.
