修改默认启动项：

sudo gedit /etc/default/grub

在打开的文本中找到 GRUB_DEFAULT 设置默认启动项（从0开始，开机时看到的若干个启动项从上到下的依次编号）

更新启动设置：

sudo update-grub

矫正时间（Ubuntu和Window时间不一致）：Windows下以管理员身份运行终端输入代码并执行

Reg add HKLM\SYSTEM\CurrentControlSet\Control\TimeZoneInformation /v RealTimeIsUniversal /t REG_DWORD /d 1

修改默认软件源：

sudo gedit /etc/apt/sources.list

复制下列源：

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

原文件内容删不删都行，保存并退出编辑，更新：

apt-get update
apt-get upgrade