1、備份源

sudo cp  /etc/apt/sources.list /etc/apt/sources.list.bak

2、查詢系統代號

$ lsb_release -a
No LSB modules are available.
Distributor ID:	Ubuntu
Description:	Ubuntu 20.04.1 LTS
Release:	20.04
Codename:	focal

我在Ubuntu20.4上做的測試，Ubuntu 20.04.1 LTS 對應的版本代號為focal

3、查詢國內源中是否存在focal版本的源

阿里：http://mirrors.aliyun.com/ubuntu/dists/
網易：http://mirrors.163.com/ubuntu/dists/

4、制作deb源

把模板中的TODO換成 lsb_release -a 查詢出的系統代號Codename

阿里源模板如下：

deb http://mirrors.aliyun.com/ubuntu/ TODO main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ TODO-security main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ TODO-updates main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ TODO-proposed main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ TODO-backports main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ TODO main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ TODO-security main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ TODO-updates main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ TODO-proposed main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ TODO-backports main restricted universe multiverse

網易源模板如下

deb http://mirrors.163.com/ubuntu/ TODO main restricted universe multiverse
deb http://mirrors.163.com/ubuntu/ TODO-security main restricted universe multiverse
deb http://mirrors.163.com/ubuntu/ TODO-updates main restricted universe multiverse
deb http://mirrors.163.com/ubuntu/ TODO-proposed main restricted universe multiverse
deb http://mirrors.163.com/ubuntu/ TODO-backports main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ TODO main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ TODO-security main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ TODO-updates main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ TODO-proposed main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ TODO-backports main restricted universe multiverse

修改后的源

例如在ubuntu20.04中使用阿里源，修改如下

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

刪除/etc/apt/sources.list原來的內容，將上面的源復制到改文件中。

5、 更新緩存和升級

sudo apt-get update
sudo apt-get upgrade

4、ubuntu版本的代號

4.10 Warty Warthog(長疣的疣豬)
5.04 Hoary Hedgehog(灰白的刺猬)
5.10 Breezy Badger(活潑的獾)6.06(LTS) Dapper Drake(整潔的公鴨)
6.10 Edgy Eft(急躁的水蜥)
7.04 Feisty Fawn(壞脾氣的小鹿)
7.10 Gutsy Gibbon(勇敢的長臂猿)8.04(LTS) Hardy Heron(耐寒的蒼鷺)
8.10 Intrepid Ibex (勇敢的野山羊)
9.04 Jaunty Jackalope(得意洋洋的懷俄明野兔)
9.10 Karmic Koala(幸運的考拉)10.04(LTS) Lucid Lynx(清醒的猞猁)
10.10 Oneiric Ocelot(夢幻的豹貓)
11.04 Natty Narwhal(敏捷的獨角鯨)
11.10 Oneiric Ocelot（有夢的虎貓）12.04(LTS) Precise Pangolin(精準的穿山甲)
12.10 Quantal Quetzal(量子的綠咬鵑)
13.04 Raring Ringtail(鉚足了勁的貓熊)
13.10 Saucy Salamander(活潑的蠑螈)14.04(LTS) Trusty Tahr (可靠的塔爾羊)(LTS)
14.10 Utopic Unicorn(烏托邦獨角獸)
15.04 Vivid Vervet (活潑的小猴)
15.10 Wily Werewolf (狡猾的狼人)16.04(LTS) Xenial Xerus (好客的非洲地松鼠)
16.10 Yakkety Yak（牦牛）
17.04 Zesty Zapus(開心的跳鼠)
17.10 Artful Aardvark(機靈的土豚)18.04(LTS) Bionic Beaver（仿生海貍）
18.10 Cosmic Cuttlefish（宇宙墨魚）
19.04 Disco Dingo（舞動的靈犬）
19.10 Eoan Ermine（白貂）20.04(LTS) Focal Fossa（專注的馬達加斯加長尾貍貓）