一、问题：

安装完ros后，需要执行sudo rosdep init，但是在没有全局科学上网的前提下，执行sudo rosdep init势必会报错：

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.

导致无法进行下一步rosdep update，其他改试图对墙做事情的方法时效性差，而且往往都是玄学。。。

这里在总结前人成果的基础上给出一个相对简单快捷的办法

二、方案:

1.新建脚本文件set_rosdep.sh包含以下内容

#! /usr/bin/env bash
## for ubuntu 20.04 & ros noetic onlyecho -e "\n\033[1;32m>>> Only for UBUNTU [20.04] & ROS [noetic] <<<\033[0m\n"
if [ ${#} -ne 0 ]; thenecho -e "Usage: \033[1;31mbash ${0}\033[0m\n" ; exit 1
fi
L_USER=${USER}
sudo git clone https://github.com/ros/rosdistro.git /opt/ros/noetic/rosdistro
if [ ${?} -ne 0 ]; then  echo -e "\033[0;31m\nERROR: git clone failed !\033[1m"; exit 1; 
fi
sudo sed -i 's/https:\/\/raw.githubusercontent.com\/ros\/rosdistro\/master/file:\/\/\/opt\/ros\/noetic\/rosdistro/g' /opt/ros/noetic/rosdistro/rosdep/sources.list.d/20-default.list
sudo rosdep init > /dev/null
sudo mkdir -p /etc/ros/rosdep/sources.list.d
sudo cp /opt/ros/noetic/rosdistro/rosdep/sources.list.d/20-default.list /etc/ros/rosdep/sources.list.d/
sudo sed -i 's/https:\/\/raw.githubusercontent.com\/ros\/rosdistro\/master/file:\/\/\/opt\/ros\/noetic\/rosdistro/g' /usr/lib/python3/dist-packages/rosdistro/__init__.py
sudo sed -i 's/https:\/\/raw.githubusercontent.com\/ros\/rosdistro\/master/file:\/\/\/opt\/ros\/noetic\/rosdistro/g' /usr/lib/python3/dist-packages/rosdep2/rep3.py
sudo sed -i "s/https:\/\/raw.githubusercontent.com\/ros\/rosdistro/file:\/\/\/opt\/ros\/noetic\/rosdistro/g" /usr/lib/python3/dist-packages/rosdep2/gbpdistro_support.py
sudo sed -i "s/master\/releases\/fuerte.yaml/releases\/fuerte.yaml/g" /usr/lib/python3/dist-packages/rosdep2/gbpdistro_support.py
sudo -u ${L_USER} rosdep update
if [ ${?} -eq 0 ]; then echo -e "\n\033[1;32m>>> Successfully executed 'rosdep update' :) <<< \033[0m\nby streamwill" ; exit 0
else echo -e "\033[0;31m\nFailed to execute 'rosdep update' !\033[1m" ; exit 1

2.运行脚本set_rosdep.sh完成rosdep update

bash set_rosdep.sh

NOTE: 执行期间应该要输入root密码，输入后回车即可。

3.Successfully executed ‘rosdep update’ 😃

--->>> 一键操作__简单快捷 <<<---

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三、！！！以下为自己操作详细步骤，可以跳过！！！

1. 下载rosdistro到本地

• 下载方式1： 度娘rosdistro，取货码: jhkn
• 下载方式2：git clone https://github.com/ros/rosdistro.git
• 必须保证文件夹名为rosdistro，且必须在当前用户目录下，即~，形如~/rosdistro。(只为保证后续直接复制命令执行)

2. 复制rosdistro文件夹到ros安装路径

• 复制文件夹rosdistro/到路径/opt/ros/noetic：

sudo cp ~/rosdistro/ /opt/ros/noetic/ -r

3.修改20-default.list文件

• 修改/opt/ros/noetic/rosdistro/rosdep/sources.list.d/20-default.list文件

sudo sed -i 's/https:\/\/raw.githubusercontent.com\/ros\/rosdistro\/master/file:\/\/\/opt\/ros\/noetic\/rosdistro/g' /opt/ros/noetic/rosdistro/rosdep/sources.list.d/20-default.list

4.复制20-default.list文件

• 复制/opt/ros/noetic/rosdistro/rosdep/sources.list.d/20-default.list文件到路径/etc/ros/rosdep/sources.list.d/

sudo cp /opt/ros/noetic/rosdistro/rosdep/sources.list.d/20-default.list /etc/ros/rosdep/sources.list.d/

• 如果没有路径/etc/ros/rosdep/sources.list.d/，则手动创建：

sudo mkdir -p /etc/ros/rosdep/sources.list.d

• 然后再次执行复制命令

sudo cp /opt/ros/noetic/rosdistro/rosdep/sources.list.d/20-default.list /etc/ros/rosdep/sources.list.d/

5. 修改三个.py文件

• 文件一：/usr/lib/python3/dist-packages/rosdistro/__init__.py

sudo sed -i 's/https:\/\/raw.githubusercontent.com\/ros\/rosdistro\/master/file:\/\/\/opt\/ros\/noetic\/rosdistro/g' /usr/lib/python3/dist-packages/rosdistro/__init__.py

• 文件二：/usr/lib/python3/dist-packages/rosdep2/rep3.py

sudo sed -i 's/https:\/\/raw.githubusercontent.com\/ros\/rosdistro\/master/file:\/\/\/opt\/ros\/noetic\/rosdistro/g' /usr/lib/python3/dist-packages/rosdep2/rep3.py

• 文件三：/usr/lib/python3/dist-packages/rosdep2/gbpdistro_support.py

sudo sed -i "s/https:\/\/raw.githubusercontent.com\/ros\/rosdistro/file:\/\/\/opt\/ros\/noetic\/rosdistro/g" /usr/lib/python3/dist-packages/rosdep2/gbpdistro_support.py

sudo sed -i "s/master\/releases\/fuerte.yaml/releases\/fuerte.yaml/g" /usr/lib/python3/dist-packages/rosdep2/gbpdistro_support.py

6.执行rosdep update完成ros-noetic更新

Successfully executed ‘rosdep update’

一键操作，简单快捷。 😃

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REF

[1].Ubuntu20.04 rosdep update失败解决方法