背景
有時使用apt-get安裝依賴庫或軟件時，看到15KB~40KB的速度下載，真的是恨鐵不成剛，爲什麼不能快一些呢；明明電腦下載時都有1M~3M的，感到無奈，一直在等待安裝。如果排除是電腦本身網絡速度慢問題，那很有可能是安裝依賴庫或軟件是外網的，需要從外網那裏獲取；這樣自然就很慢啦。
修改成國內軟件源（apt-get）
1. 備份原始文件
sudo cp /etc/apt/sources.list /etc/apt/sources.list2
2.修改 sources.list 文件的權限
sudo chmod 777 /etc/apt/sources.list
3. 修改文件並添加國內源
vi /etc/apt/sources.list
不喜歡用 vi 編譯器的可以使用 gedit
gedit /etc/apt/sources.list
4.註釋原文件內的源並添加如下地址
不同的系統版本對應的軟件源也是不一樣的，之前被坑了；以爲ubuntu系統下，使用的軟件源應該都一樣的，後來發現替換源後，部分軟件無法安裝，經過調查發現不同的系統版本對應的不同的軟件源；
比如同一個品牌的軟件源（網易163），也會區分是ubuntu18、ubuntu16還是ubuntu14系統的。
#阿里雲 （推薦）Ubuntu18
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
#網易163（這個速度比較快）Ubuntu18
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
#阿里雲 （推薦）Ubuntu16
deb http://mirrors.aliyun.com/ubuntu/ xenial main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ xenial-security main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ xenial-updates main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ xenial-proposed main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ xenial-backports main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ xenial main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ xenial-security main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ xenial-updates main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ xenial-proposed main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ xenial-backports main restricted universe multiverse
#網易163（這個速度比較快）Ubuntu16
deb http://mirrors.aliyun.com/ubuntu/ xenial main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ xenial-security main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ xenial-updates main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ xenial-proposed main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ xenial-backports main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ xenial main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ xenial-security main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ xenial-updates main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ xenial-proposed main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ xenial-backports main restricted universe multiverse
#網易163（這個速度比較快）Ubuntu14
deb http://mirrors.163.com/ubuntu/ trusty main restricted universe multiverse
deb http://mirrors.163.com/ubuntu/ trusty-security main restricted universe multiverse
deb http://mirrors.163.com/ubuntu/ trusty-updates main restricted universe multiverse
deb http://mirrors.163.com/ubuntu/ trusty-proposed main restricted universe multiverse
deb http://mirrors.163.com/ubuntu/ trusty-backports main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ trusty main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ trusty-security main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ trusty-updates main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ trusty-proposed main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ trusty-backports main restricted universe multiverse
軟件源-分析
每一行的開頭的deb或者deb-src，分別表示通過.deb文件、源文件的方式進行安裝。URL後面的5個用空格隔開的字符串，分別對應相應的目錄結構。
1）當我們打開URL，比如Ubuntu14 的網易軟件源的，http://mirrors.163.com/ubuntu/ 會看到如下圖的目錄結構：
2）進入dists目錄，可以發現trusty、trusty-security、trusty-updates、trusty-proposed、trusty-backports 五個目錄：
3）trusty、trusty-security、trusty-updates、trusty-proposed、trusty-backports 後面四個字段對應子目錄：
deb http://mirrors.163.com/ubuntu/ trusty main restricted universe multiverse
細心對比後會發現以下規律：
| 系統版本 | Ubuntu14 | Ubuntu16 | Ubuntu18 |
| 軟件源--關鍵字 | trusty | xenial | bionic |
5,更新源
sudo apt-get update
6. 更新軟件( 可選)
sudo apt-get dist-upgrade
sudo apt-get upgrade
由於包與包之間存在各種依賴關係。upgrade只是簡單的更新包，不管這些依賴，它不和添加包，或是刪除包。而dist-upgrade可以根據依賴關係的變化，添加包，刪除包。
upgrade:系統將現有的Package升級,如果有相依性的問題,而此相依性需要安裝其它新的Package或影響到其它Package的相依性時,此Package就不會被升級,會保留下來. dist-upgrade:可以聰明的解決相依性的問題,如果有相依性問題,需要安裝/移除新的Package,就會試着去安裝/移除它. (所以通常這個會被認爲是有點風險的升級)
希望對你有幫助；
如果有更新或不對的地方歡迎指正。