前言
由于Ubuntu18经常出错，因而决定回退Ubuntu16，下面是记录回退问题及美化，以便以后需要。
问题总结
磁盘挂载
挂载其他磁盘分区时，提示错误“Metadata kept in Windows cache, refused to mount.”，执行下面命令即可修复。
sudo ntfsfix /dev/sdad
若是提示错误“Windows is hibernated, refused to mount.”，则关闭Windows的快速启动。
双系统时间不一致
Windows与Ubuntu的时间不一样，执下面的命令即可。
sudo timedatectl set-local-rtc 1
安装chrome
sudo wget http://www.linuxidc.com/files/repo/google-chrome.list -P /etc/apt/sources.list.d/
wget -q -O - https://dl.google.com/linux/linux_signing_key.pub | sudo apt-key add -
sudo apt update
sudo apt install google-chrome-stable
更换APT源
修改文件/etc/apt/sources.list为下面内容，以更换为阿里的源。
# deb cdrom:[Ubuntu 16.04 LTS _Xenial Xerus_ - Release amd64 (20160420.1)]/ xenial main restricted
deb-src http://archive.ubuntu.com/ubuntu xenial main restricted #Added by software-properties
deb http://mirrors.aliyun.com/ubuntu/ xenial main restricted
deb-src http://mirrors.aliyun.com/ubuntu/ xenial main restricted multiverse universe #Added by software-properties
deb http://mirrors.aliyun.com/ubuntu/ xenial-updates main restricted
deb-src http://mirrors.aliyun.com/ubuntu/ xenial-updates main restricted multiverse universe #Added by software-properties
deb http://mirrors.aliyun.com/ubuntu/ xenial universe
deb http://mirrors.aliyun.com/ubuntu/ xenial-updates universe
deb http://mirrors.aliyun.com/ubuntu/ xenial multiverse
deb http://mirrors.aliyun.com/ubuntu/ xenial-updates multiverse
deb http://mirrors.aliyun.com/ubuntu/ xenial-backports main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ xenial-backports main restricted universe multiverse #Added by software-properties
deb http://archive.canonical.com/ubuntu xenial partner
deb-src http://archive.canonical.com/ubuntu xenial partner
deb http://mirrors.aliyun.com/ubuntu/ xenial-security main restricted
deb-src http://mirrors.aliyun.com/ubuntu/ xenial-security main restricted multiverse universe #Added by software-properties
deb http://mirrors.aliyun.com/ubuntu/ xenial-security universe
deb http://mirrors.aliyun.com/ubuntu/ xenial-security multiverse
美化
更换为Gnome桌面
先卸载Unity桌面及Lightdm，执行下面命令。
apt purge unity*
apt purge lightdm
最小化安装Gnome及安装Gdm，执行下面命令。
apt install gnome-shell
apt install gdm
最后重启即可。
美化Gnome桌面
先安装gnome-tweak-tool
apt install gnome-tweak-tool
安装以下Gnome Shell extension
- Topicon plus
- Dash to dock
执行下面命令，安装Numxi图标
sudo apt-add-repository ppa:numix/ppa
sudo apt-get update
sudo apt-get install numix-icon-theme-circle