一、报错

1.1 sudo rosdep init报错

????????sudo rosdep init时会由于网络问题报错：

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.

示例如下:

meng@meng:~$ sudo rosdep init
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.

1.2 rosdep update报错

??????? 同时当sudo rosdep init成功后，同样会因为网络问题而在执行rosdep update时卡住 ??????

二、报错解决与理论分析

2.1 下载rosdep文件到本地(不能访问github可以留下邮箱)

??????? rosdep是ros的“依赖项”，ros运行一般需要这些文件；rosdep官方github地址为:https://github.com/ros/rosdistro

??????? 进入网站，可以看出，只有少部分文件在近期更新，一般不是很影响(如果怕影响可以定期更新下载的文件并进行替换)，直接下载即可（举个例子，我在大四下自己用自己下载的rosdep到自己的笔记本上用，现在研一下了还可以用）

???????? 下载命令为:(如果新电脑无法下载，可以用别的电脑下载并拷贝过来)

git clone https://github.com/ros/rosdistro

2.2 创建并修改20-default.list文件

??????? 没有20-default.list文件时，创建命令如下：（有的话直接打开修改即可）

mkdir -p /etc/ros/rosdep/sources.list.d/20-default.list

??????? 并打开/etc/ros/rosdep/sources.list.d/20-default.list进行修改：

sudo gedit /etc/ros/rosdep/sources.list.d/20-default.list

??????? 填入并修改以下文件地址：（注：file://是本地文件链接方式，不同于https等）

    yaml file:///home/xxx/rosdistro/rosdep/osx-homebrew.yaml osx

	# generic 
	yaml file:///home/xxx/rosdistro/rosdep/base.yaml
	yaml file:///home/xxx/rosdistro/rosdep/python.yaml
	yaml file:///home/xxx/rosdistro/rosdep/ruby.yaml
	gbpdistro file:///home/xxx/rosdistro/releases/fuerte.yaml fuerte

??????? 文件地址可以从2.1下载的文件中获得:

2.3 修改/usr/lib/python2.7/dist-packages/rosdep2/目录下文件

2.3.1 sources_list.py

??????? 打开文件:

sudo gedit /usr/lib/python2.7/dist-packages/rosdep2/sources_list.py

??????? 在第75行左右，修改DEFAULT_SOURCES_LIST_URL = ‘file:///etc/ros/rosdep/sources.list.d/20-default.list’，其中file:///etc/ros/rosdep/sources.list.d/20-default.list为在2.2中创建文件的地址，示例如下：

# default file to download with 'init' command in order to bootstrap
# rosdep
#DEFAULT_SOURCES_LIST_URL = 'https://raw.githubusercontent.com/ros/rosdistro/master/rosdep/sources.list.d/20-default.list'
DEFAULT_SOURCES_LIST_URL = 'file:///etc/ros/rosdep/sources.list.d/20-default.list'

2.3.2 rep3.py

sudo gedit /usr/lib/python2.7/dist-packages/rosdep2/rep3.py

??????? 修改 REP3_TARGETS_URL为本地targets.yaml文件地址，targets.yaml在2.1步骤下载的文件夹里面：

?????

??????? 修改第39行左右，示例如下：

# location of targets file for processing gbpdistro files
#REP3_TARGETS_URL = 'https://raw.github.com/ros/rosdistro/master/releases/targets.yaml'
REP3_TARGETS_URL = 'file:///home/bit/Desktop/softwares/ros_install/rosdistro/releases/targets.yaml' #hxz

2.3.3 init.py

 sudo gedit /usr/lib/python2.7/dist-packages/rosdistro/__init__.py

??????? 注：这个文件如果找不到，试着找init.py这个文件，但一般都是__init__.py

 sudo gedit /usr/lib/python2.7/dist-packages/rosdistro/init.py

??????? 修改DEFAULT_INDEX_URL 为2.1步骤下载的文件路径 'file:///media/meng/xx/ros_install/rosdistro/index-v4.yaml'

??????? 修改示例如下:

# index information

#DEFAULT_INDEX_URL = 'https://raw.githubusercontent.com/ros/rosdistro/master/index-v4.yaml'
DEFAULT_INDEX_URL = 'file:///home/bit/Desktop/softwares/ros_install/rosdistro/index-v4.yaml' #hxz

2.4 rosdep?update

sudo rosdep init #maybe be error,but don't worry
rosdep update

3 进一步理论分析

3.1 sudo rosdep init无法访问的链接：

??????? 打开报错的链接:(从链接可以看出，该链接指向一个文件)

https://raw.githubusercontent.com/ros/rosdistro/master/rosdep/sources.list.d/20-default.list

??????? 网页为文本呈现，内容为:

# 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