[ROS Solution] rosdep init && rosdep update 失败

1. rosdep init 失败的解决办法

	有时由于服务器，网络等问题，无法执行rosdep init操作，可以手动创建20-default.list文件，然后进行rosdep update操作。

1.2 Error

	#出现如下错误
	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.

1.3 手动创建20-default.list文件

	$ sudo nano /etc/ros/rosdep/sources.list.d/20-default.list
	
	# 然后将下面的内容拷贝到文件中保存即可
	# 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

1.4 更新

	$ rosdep update

2. rosdep update 失败的解决办法

	无法执行rosdep update操作，可以先更新Ubuntu，再更新ROS。

2.1 Error

	#出现timeout错误
	reading in sources list data from /etc/ros/rosdep/sources.list.d
	ERROR: unable to process source [https://raw.githubusercontent.com/ros/rosdistro/master/rosdep/osx-homebrew.yaml]:
		 (https://raw.githubusercontent.com/ros/rosdistro/master/rosdep/osx-homebrew.yaml)
	ERROR: unable to process source [https://raw.githubusercontent.com/ros/rosdistro/master/rosdep/base.yaml]:
		 (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)
	ERROR: unable to process source [https://raw.githubusercontent.com/ros/rosdistro/master/rosdep/ruby.yaml]:
		 (https://raw.githubusercontent.com/ros/rosdistro/master/rosdep/ruby.yaml)
	ERROR: unable to process source [https://raw.githubusercontent.com/ros/rosdistro/master/releases/fuerte.yaml]:
		Failed to download target platform data for gbpdistro:
		

2.2 更新Ubuntu

	$ sudo apt-get update

2.3 更新ROS

	$ rosdep update

3. Ubuntu18.04安装ROS-melodic

	#添加中科大的ROS镜像源
	$ sudo sh -c '. /etc/lsb-release && echo "deb http://mirrors.ustc.edu.cn/ros/ubuntu/DISTRIB_CODENAME main" > /etc/apt/sources.list.d/ros-latest.list'
	
	#配置key,原先4开头的key禁用了，换成下面的key
	$ sudo apt-key del 421C365BD9FF1F717815A3895523BAEEB01FA116
	$ sudo -E apt-key adv --keyserver 'hkp://keyserver.ubuntu.com:80' --recv-key C1CF6E31E6BADE8868B172B4F42ED6FBAB17C654
	
	#更新
	$ sudo apt-get update
	
	#安装melodic桌面完整版
	$ sudo apt-get install ros-melodic-desktop-full
	
	#初始化rosdep
	$ sudo rosdep init
	
	#ROS更新
	$ rosdep update
	
	#配置环境变量 source
	$ echo "source /opt/ros/melodic/setup.bash" >> ~/.bashrc
	$ source ~/.bashrc
	
	#创建工作空间
	$ mkdir -p ~/catkin_ws/src
	$ cd ~/catkin_ws/src
	$ catkin_init_workspace
	
	#编译并配置工作空间
	$ cd ..
	$ catkin_make
	$ echo "source ~/catkin_ws/devel/setup.bash">> ~/.bashrc

Reference

[1] ROS Melodic安装教程[EB/OL]. 2019.
[2] ROS国内镜像源[EB/OL]. 2019.