Ubuntu16.04无法更新apt，一直报错

问题遇到的现象和发生背景

我是在VirtualBox里用的Ubuntu，安装好后一直无法更新apt。
图一是从系统设置里换源的问题；图二是终端出现的问题

操作环境、软件版本等信息

Ubuntu版本是16.04，VirtualBox里使用的Ubuntu

尝试过的解决方法

试过换各种源都失败了，已经折磨我三天了。

我想要达到的结果

希望各位帮我解答一下什么原因，怎么解决

感谢邀请
更新失败的可能原因
1，网络原因
2，ubuntu16 自带的源不好用，或者有问题
解决方法可以参考这篇文章
Ubuntu apt update（apt-get update）报错、失败_墨痕诉清风的博客-CSDN博客_apt update失败
执行sudo apt-get update失败的解决方案_Jane_sl的博客-CSDN博客
如有帮助，采纳一下

修改源的时候，把原来指向ubuntu自己服务器的地址全部注释掉。都指向阿里云的服务器上。

执行如下命令，更新软件源

sudo rm  /var/lib/dpkg/lock
sudo apt clean
sudo rm /var/lib/dpkg/updates/*
sudo apt update

先解决网络问题，再检查安装源（换一台试试源是否OK）。可以把换源的文件内容展示出来，方便查问题。

那个优麒麟的源有问题

1：换源

sudo cp /etc/apt/sources.list /etc/apt/sources.list.bak
sudo gedit /etc/apt/sources.list

#复制下面的所有内容替换掉原文件中的所有内容(一次只可以选一个镜像源，根据你的情况选)

#  阿里源
deb http://mirrors.aliyun.com/ubuntu/ bionic main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ bionic-security main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ bionic-updates main restricted universe multiverse
deb 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 main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ bionic-security main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ bionic-updates main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ bionic-proposed main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ bionic-backports main restricted universe multiverse

 # 清华源
 deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ bionic main restricted universe multiverse
 deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ bionic main restricted universe multiverse
 deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ bionic-updates main restricted universe multiverse
 deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ bionic-updates main restricted universe multiverse
 deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ bionic-backports main restricted universe multiverse
 deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ bionic-backports main restricted universe multiverse
 deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ bionic-security main restricted universe multiverse
 deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ bionic-security main restricted universe multiverse
 deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ bionic-proposed main restricted universe multiverse
 deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ bionic-proposed main restricted universe multiverse

2：

sudo apt update 
sudo apt upgrade

【1】 sudo cp /etc/apt/sources.list /etc/apt/sources.list_backup    先将之前的下载源备份一下 
               【2】sudo vim /etc/apt/sources.list                                   打开这个文件准备修改
               【3】添加清华园的下载源（下载源在下方，复制粘贴就行），粘贴到这个文件夹下就可以
               【4】sudo apt-get update     更新一下

# 默认注释了源码镜像以提高 apt update 速度，如有需要可自行取消注释
deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ xenial main restricted universe multiverse
# deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ xenial main restricted universe multiverse
deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ xenial-updates main restricted universe multiverse
# deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ xenial-updates main restricted universe multiverse
deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ xenial-backports main restricted universe multiverse
# deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ xenial-backports main restricted universe multiverse
deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ xenial-security main restricted universe multiverse
# deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ xenial-security main restricted universe multiverse