问题描述
使用 sudo apt get-install 出现E: Failed to fetch问题。
更换镜像源
错误原因：绝大多数情况下，ROS更新的下载源都是正常的，所以出现这个问题，应该是自己系统一些配置设置问题。
既然网络出现问题，我们更换下载源：
使用gedit或vi/vim打开配置文件:
sudo gedit /etc/apt/sources.list
或者
sudo vim /etc/apt/sources.list
替换里面全部内容
deb http://mirrors.aliyun.com/ubuntu/ bionic main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ bionic main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ bionic-security main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ bionic-security main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ bionic-updates main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ bionic-updates main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ bionic-proposed main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ bionic-proposed main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ bionic-backports main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ bionic-backports main restricted universe multiverse
or
然后生效配置文件（刷新列表）
sudo apt-get update
注意：一定要执行刷新
配置DNS网关
Terminal下输入命令
sudo gedit /etc/resolv.conf
或者
sudo vi /etc/resolv.conf
在resolv.conf里面添加阿里DNS
nameserver 127.0.0.53
sudo apt-get update