ubuntu server 官方的源代码更新比较慢，所以更替成国内的源。
从下面几个国内的镜像源任选一个即可，配置到ubuntu 20.04的apt配置文件里，编辑如下文件：
/etc/apt/sources.list
编辑文件完成后，执行如下命令进行更新缓存：
sudo apt update sudo apt upgrade
阿里云镜像源：
deb http://mirrors.aliyun.com/ubuntu/ focal main restricted universe multiverse deb-src http://mirrors.aliyun.com/ubuntu/ focal main restricted universe multiverse deb http://mirrors.aliyun.com/ubuntu/ focal-security main restricted universe multiverse deb-src http://mirrors.aliyun.com/ubuntu/ focal-security main restricted universe multiverse deb http://mirrors.aliyun.com/ubuntu/ focal-updates main restricted universe multiverse deb-src http://mirrors.aliyun.com/ubuntu/ focal-updates main restricted universe multiverse deb http://mirrors.aliyun.com/ubuntu/ focal-proposed main restricted universe multiverse deb-src 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-backports main restricted universe multiverse
清华大学镜像源:
deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ focal main restricted universe multiverse # deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ focal main restricted universe multiverse deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ focal-updates main restricted universe multiverse # deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ focal-updates main restricted universe multiverse deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ focal-backports main restricted universe multiverse # deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ focal-backports main restricted universe multiverse deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ focal-security main restricted universe multiverse # deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ focal-security main restricted universe multiverse # deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ focal-proposed main restricted universe multiverse # deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ focal-proposed main restricted universe multiverse
网易镜像源：
deb http://mirrors.163.com/ubuntu/ focal main restricted universe multiverse deb http://mirrors.163.com/ubuntu/ focal-security main restricted universe multiverse deb http://mirrors.163.com/ubuntu/ focal-updates main restricted universe multiverse deb http://mirrors.163.com/ubuntu/ focal-proposed main restricted universe multiverse deb http://mirrors.163.com/ubuntu/ focal-backports main restricted universe multiverse deb-src http://mirrors.163.com/ubuntu/ focal main restricted universe multiverse deb-src http://mirrors.163.com/ubuntu/ focal-security main restricted universe multiverse deb-src http://mirrors.163.com/ubuntu/ focal-updates main restricted universe multiverse deb-src http://mirrors.163.com/ubuntu/ focal-proposed main restricted universe multiverse deb-src http://mirrors.163.com/ubuntu/ focal-backports main restricted universe multiverse
中科大镜像源：
deb https://mirrors.ustc.edu.cn/ubuntu/ focal main restricted universe multiverse deb-src https://mirrors.ustc.edu.cn/ubuntu/ focal main restricted universe multiverse deb https://mirrors.ustc.edu.cn/ubuntu/ focal-updates main restricted universe multiverse deb-src https://mirrors.ustc.edu.cn/ubuntu/ focal-updates main restricted universe multiverse deb https://mirrors.ustc.edu.cn/ubuntu/ focal-backports main restricted universe multiverse deb-src https://mirrors.ustc.edu.cn/ubuntu/ focal-backports main restricted universe multiverse deb https://mirrors.ustc.edu.cn/ubuntu/ focal-security main restricted universe multiverse deb-src https://mirrors.ustc.edu.cn/ubuntu/ focal-security main restricted universe multiverse deb https://mirrors.ustc.edu.cn/ubuntu/ focal-proposed main restricted universe multiverse deb-src https://mirrors.ustc.edu.cn/ubuntu/ focal-proposed main restricted universe multiverse
apt使用
apt-get update #更新索引
apt-cache search nginx #搜索关键字还有nginx的包
apt-get install nginx #安装nginx
然后会出现key无法找到。
然后执行：
piaoyun@Ubuntu:~$ sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys < add keys here >
piaoyun@Ubuntu:~$ sudo apt-get update
解决ubuntu server 12.04更换源后gpg错误的解决办法。
更换了一个更快的源，使用sudo apt-get update报了一个gig错误： W: GPG error: http://extras.ubuntu.com precise Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 16126D3A3E5C1192
使用google查询到解决办法：
$gpg --keyserver keyserver.ubuntu.com --recv 3E5C1192 $gpg --export --armor 3E5C1192 | sudo apt-key add -
$sudo apt-get update
若执行apt-get update产生错误【错误现象】E: Could not get lock /var/lib/apt/lists/lock - open (11 Resource temporarily unavailable) E: Unable to lock the list directory【错误原因】可能为之前操作使用ctrl+c强制退出apt-get 指令，而实际apt-get进程依然存在。
【解决方法】查看进程(使用grep指令过滤其他进程)
ps -e | grep apt
apt-get进程依然存在6362 ? 00:00:00 apt 6934 ? 00:00:00 apt-get销毁进程sudo killall apt sudo killall apt-get重新执行sudo apt-get update
