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一、更换ROS软件源

1、添加ROS安装源

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'

2、设置密钥

sudo apt-key adv --keyserver 'hkp://keyserver.ubuntu.com:80' --recv-key C1CF6E31E6BADE8868B172B4F42ED6FBAB17C654

3、更新软件源

sudo apt update

升级了 0 个软件包，新安装了 0 个软件包，要卸载 0 个软件包，有 **个软件包未被升级

sudo apt-get upgrade

二、安装ROS

1.安装ROS

Ubuntu 20.04安装Ros Noetic 及 18.04安装ROS Melodic

sudo apt install ros-noetic-desktop-full

2.初始化 rosdep

sudo rosdep init

错误1：找不到命令（rosdep找不到命令）

sudo apt install python3-rosdep2

错误2：

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.

该错误与rosdep update相似，处理方式差不多
本人处理方式，参照文献1、文献2、文献3，三种处理方式都是将源文件下载下来，根据自己情况，所放的目录位置不同。
原文件地址：地址1、地址2

下面是本人位置
针对错误2，找到/usr/lib/python2.7/dist-packages/rosdep2/sources_list.py文件，修改：

# rosdep
DEFAULT_SOURCES_LIST_URL = 'file:///home/xxx/rosdistro/rosdep/sources.list.d/20-default.list'

其中文件20-default.list要重新配置

# os-specific listings first

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

# generic

yaml file:///home/***/rosdistro/rosdep/base.yaml
yaml file:///home/***/rosdistro/rosdep/python.yaml
yaml file:///home/***/rosdistro/rosdep/ruby.yaml
gbpdistro file:///home/***/rosdistro/releases/fuerte.yaml fuerte

# newer distributions (Groovy, Hydro, ...) must not be listed anymore, they are being fetched from the rosdistro index.yaml instead

再次运行sudo rosdep init
如果出现下面错误，就删除20-default.list文件，是因为该文件是旧文件，无法更新：

ERROR: default sources list file already exists: /etc/ros /rosdep/sources.list.d/20-default.listPlease delete if you wish to re-initialize

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

再次运行sudo rosdep init

3、更新 rosdep

rosdep update

rosdep更新超时问题

注意文件路径

文件1：/usr/lib/python2.7/dist-packages/rosdep2/rep3.py

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

修改位置

# REP3_TARGETS_URL = 'https://raw.githubusercontent.com/ros/rosdistro/master/releases/targets.yaml'
REP3_TARGETS_URL = 'file:///home/***/rosdistro/releases/targets.yaml'

文件2：/usr/lib/python2.7/dist-packages/rosdistro/__init__.py

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

修改位置

# DEFAULT_INDEX_URL = 'https://raw.githubusercontent.com/ros/rosdistro/master/index-v4.yaml'
DEFAULT_INDEX_URL = 'file:///home/***/rosdistro/index-v4.yaml'

再次运行rosdep update

4、设置环境变量

echo "source /opt/ros/noetic/setup.bash" >> ~/.bashrc

source ~/.bashrc

5、安装 rosinstall

sudo apt install python3-rosinstall python3-rosinstall-generator python3-wstool

sudo apt install python3-roslaunch

sudo apt install ros-noetic-desktop-full

三、运行海龟

命令框 1：

roscore

命令框 2：

rosrun turtlesim turtlesim_node

命令框 3：

rosrun turtlesim turtle_teleop_key

修改海龟形状的文件夹在/opt/ros/humble/share/turtlesim/images中