ubuntu 20 ros安装 安装成功后 roscore后报错

sudo rosdep init
rosdep update
成功后 启动核心报以下错误
Resource not found: roslaunch
The traceback for the exception was written to the log file

原来是未设置启动项 设置以下命令
echo "source /opt/ros/noetic/setup.bash" >> ~/.bashrc
source ~/.bashrc
刷新环境变量后执行roscore，正常运行