sudo rosdep init and rosdep update Error 解决方法

错误如下：

$ sudo rosdep init
ERROR: default sources list file already exists:
/etc/ros/rosdep/sources.list.d/20-default.list
Please delete if you wish to re-initialize
Then you can execute
 

$ rosdep update
If you get
reading in sources list data from /etc/ros/rosdep/sources.list.d
Hit https://raw.githubusercontent.com/ros/rosdistro/master/rosdep/osx-homebrew.yaml
Hit https://raw.githubusercontent.com/ros/rosdistro/master/rosdep/base.yaml
ERROR: unable to process source [https://raw.githubusercontent.com/ros/rosdistro/master/rosdep/python.yaml]:
(https://raw.githubusercontent.com/ros/rosdistro/master/rosdep/python.yaml)
then you can execute the following command:
 

解决方法：

命令行中输入以下代码：

sudo gedit /etc/resolv.conf

修改resolv.conf，改成下面两句：

nameserver 8.8.8.8 #google域名服务器

nameserver 8.8.4.4 #google域名服务器