简要说明：
这个问题来源于系统的源设置。由于我们并不太信任国内资源，因此全部直接使用美国源。
平时有碰到太多运营商利用DNS，做到私自替换同名文件经历，特别是http的链接尤为严重。

解决方案：
如您觉得系统更新/安装软件速度慢，请替换使用中国内地源地址(阿里或163,二选一)。
阿里源：https://opsx.alibaba.com/mirror
163源：https://mirrors.163.com/

备注：
1：如果替换源后发现更新会超时或失败，请编辑源文件,将里面的源地址连接由http改成https
2：国内服务器建议使用163源或阿里云源。海外服务器也可以使用阿里云源(阿里源有海外节点)
3：查询系统版本号命令：lsb_release -a

CentOS系统：
1、先安装wget命令及备份原文件：
yum install -y wget && mv /etc/yum.repos.d/CentOS-Base.repo /etc/yum.repos.d/CentOS-Base.repo.backup

2、下载新的CentOS-Base.repo 到/etc/yum.repos.d/
备注：海外节点用阿里云，国内节点阿里或163都可以.
CentOS 6：
阿里源：wget -O /etc/yum.repos.d/CentOS-Base.repo http://mirrors.aliyun.com/repo/Centos-6.repo
163源：wget -O /etc/yum.repos.d/CentOS-Base.repo http://mirrors.163.com/.help/CentOS6-Base-163.repo
CentOS 7：
阿里源：wget -O /etc/yum.repos.d/CentOS-Base.repo http://mirrors.aliyun.com/repo/Centos-7.repo
163源：wget -O /etc/yum.repos.d/CentOS-Base.repo http://mirrors.163.com/.help/CentOS7-Base-163.repo

3：下载完成后,修改源文件连接为https
编辑/etc/yum.repos.d/CentOS-Base.repo，将里面所有的http修改为https

4：最后清理升级并重新生成缓存
yum clean all && yum makecache

Debian系统：
1、先安装 apt-get update && apt-get install -y apt-transport-https
2、编辑 /etc/apt/sources.list , 删除所有默认的源并替换为以下内容(操作前请做好相应备份)
2、替换完成后需要清理并刷新源：rm -rf /var/lib/apt/lists/* && apt-get update

Debian 10(buster)：
阿里源：
deb https://mirrors.aliyun.com/debian/ buster main
deb-src https://mirrors.aliyun.com/debian/ buster main
deb https://mirrors.aliyun.com/debian/ buster-updates main
deb-src https://mirrors.aliyun.com/debian/ buster-updates main
deb https://mirrors.aliyun.com/debian/ buster-backports main
deb-src https://mirrors.aliyun.com/debian/ buster-backports main
deb https://mirrors.aliyun.com/debian-security buster/updates main
deb-src https://mirrors.aliyun.com/debian-buster stretch/updates main

163源：
deb https://mirrors.163.com/debian/ buster main
deb-src https://mirrors.163.com/debian/ buster main
deb https://mirrors.163.com/debian/ buster-updates main
deb-src https://mirrors.163.com/debian/ buster-updates main
deb https://mirrors.163.com/debian/ buster-backports main
deb-src https://mirrors.163.com/debian/ buster-backports main
deb https://mirrors.163.com/debian-security/ buster/updates main
deb-src https://mirrors.163.com/debian-security/ buster/updates main

Debian 9(stretch)：
阿里源：
deb https://mirrors.aliyun.com/debian/ stretch main
deb-src https://mirrors.aliyun.com/debian/ stretch main
deb https://mirrors.aliyun.com/debian/ stretch-updates main
deb-src https://mirrors.aliyun.com/debian/ stretch-updates main
deb https://mirrors.aliyun.com/debian/ stretch-backports main
deb-src https://mirrors.aliyun.com/debian/ stretch-backports main
deb https://mirrors.aliyun.com/debian-security stretch/updates main
deb-src https://mirrors.aliyun.com/debian-security stretch/updates main

163源：
deb https://mirrors.163.com/debian/ stretch main
deb-src https://mirrors.163.com/debian/ stretch main
deb https://mirrors.163.com/debian/ stretch-updates main
deb-src https://mirrors.163.com/debian/ stretch-updates main
deb https://mirrors.163.com/debian/ stretch-backports main
deb-src https://mirrors.163.com/debian/ stretch-backports main
deb https://mirrors.163.com/debian-security/ stretch/updates main
deb-src https://mirrors.163.com/debian-security/ stretch/updates main

Debian 8(jessie)：
阿里源：
deb https://mirrors.aliyun.com/debian/ jessie main
deb-src https://mirrors.aliyun.com/debian/ jessie main
deb https://mirrors.aliyun.com/debian-security/ jessie/updates main
deb-src https://mirrors.aliyun.com/debian-security/ jessie/updates main

163源：
deb https://mirrors.163.com/debian/ jessie main
deb-src https://mirrors.163.com/debian/ jessie main
deb https://mirrors.163.com/debian-security/ jessie/updates main
deb-src https://mirrors.163.com/debian-security/ jessie/updates main

Debian 7(wheezy)：
阿里源：
deb https://mirrors.aliyun.com/debian/ wheezy main
deb-src https://mirrors.aliyun.com/debian/ wheezy main
deb https://mirrors.aliyun.com/debian-security/ wheezy/updates main
deb-src https://mirrors.aliyun.com/debian-security/ wheezy/updates main

163源：
deb https://mirrors.163.com/debian/ wheezy main
deb-src https://mirrors.163.com/debian/ wheezy main
deb https://mirrors.163.com/debian-security/ wheezy/updates main
deb-src https://mirrors.163.com/debian-security/ wheezy/updates main

Ubuntu或其他系统参考：
阿里源：https://opsx.alibaba.com/mirror （找到对应系统，找到操作那列点后面的"帮助"）
163源：https://mirrors.163.com/.help/ubuntu.html

补充说明：
国内主机请谨慎使用BBR，在连接条件好的情况下可能会反过来导致减速效果。