Ubuntu更换国内镜像源
1.备份原系统中的镜像源
sudo cp /etc/apt/sources.list /etc/apt/sources.bak1
#第一个参数时拷贝的文件路径和文件名称,第二个是拷贝到(粘贴)的文件路径和文件名
sudo cp /etc/apt/sources.list /etc/apt/sources.bak1
2.更改镜像源文件的访问权限(增加写权限)
sudo chmod u+w /etc/apt/sources.list
sudo chmod u+w /etc/apt/sources.list
更改完成可以再恢复文件的访问权限。
清华镜像源：https://mirrors.tuna.tsinghua.edu.cn/help/ubuntu/
3.更改镜像源内容
#方法 sudo gedit /etc/apt/sources.list #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 #网易源 #deb http://mirrors.163.com/ubuntu/ bionic main restricted universe multiverse #deb http://mirrors.163.com/ubuntu/ bionic-security main restricted universe multiverse #deb http://mirrors.163.com/ubuntu/ bionic-updates main restricted universe multiverse #deb http://mirrors.163.com/ubuntu/ bionic-proposed main restricted universe multiverse #deb http://mirrors.163.com/ubuntu/ bionic-backports main restricted universe multiverse #deb-src http://mirrors.163.com/ubuntu/ bionic main restricted universe multiverse #deb-src http://mirrors.163.com/ubuntu/ bionic-security main restricted universe multiverse #deb-src http://mirrors.163.com/ubuntu/ bionic-updates main restricted universe multiverse #deb-src http://mirrors.163.com/ubuntu/ bionic-proposed main restricted universe multiverse #deb-src http://mirrors.163.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 ##中科大源 deb https://mirrors.ustc.edu.cn/ubuntu/ bionic main restricted universe multiverse deb-src https://mirrors.ustc.edu.cn/ubuntu/ bionic main restricted universe multiverse deb https://mirrors.ustc.edu.cn/ubuntu/ bionic-updates main restricted universe multiverse deb-src https://mirrors.ustc.edu.cn/ubuntu/ bionic-updates main restricted universe multiverse deb https://mirrors.ustc.edu.cn/ubuntu/ bionic-backports main restricted universe multiverse deb-src https://mirrors.ustc.edu.cn/ubuntu/ bionic-backports main restricted universe multiverse deb https://mirrors.ustc.edu.cn/ubuntu/ bionic-security main restricted universe multiverse deb-src https://mirrors.ustc.edu.cn/ubuntu/ bionic-security main restricted universe multiverse deb https://mirrors.ustc.edu.cn/ubuntu/ bionic-proposed main restricted universe multiverse deb-src https://mirrors.ustc.edu.cn/ubuntu/ bionic-proposed main restricted universe multiverse
4.更新软件源列表
sudo apt-get update
#这个命令，会访问源列表里的每个网址，并读取软件列表，然后保存在本地电脑。
我们在新立得软件包管理器里看到的软件列表，都是通过update命令更新的。
sudo apt-get update
sudo apt-get upgrade
#这个命令，会把本地已安装的软件，与刚下载的软件列表里对应软件进行对比，如果发现已安装的软件版本太低，
就会提示你更新。如果你的软件都是最新版本，会提示：
升级了 0 个软件包，新安装了 0 个软件包，要卸载 0 个软件包，有 0 个软件包未被升级。
sudo apt-get upgrade
【参考1】https://blog.csdn.net/qq_21095573/article/details/99736630