更換源步驟如下：
備份源列表
sudo cp /etc/apt/sources.list /etc/apt/sources.list.bak
命令列開啟sources.list檔案
sudo gedit /etc/apt/sources.list
修改sources,list檔案【本例更改為阿里映象源】
阿里映象源
deb bionic main restricted universe multiverse
deb-src bionic main restricted universe multiverse
deb bionic-security main restricted universe multiverse
deb-src bionic-security main restricted universe multiverse
deb bionic-updates main restricted universe multiverse
deb-src bionic-updates main restricted universe multiverse
deb bionic-proposed main restricted universe multiverse
deb-src bionic-proposed main restricted universe multiverse
deb bionic-backports main restricted universe multiverse
deb-src bionic-backports main restricted universe multiverse
更新並公升級
sudo apt-get update && sudo apt-get upgrade
【注意！注意！注意】更新時一定要把linux的網路連線檢查是否已經連線上網路，不然會出錯，我之前試一直不成功，困了好久，才發現是虛擬機器的網路沒有連線。。。
更新好後就可以用命令列進行安裝軟體或者外掛程式了
最後再分享幾個國內比較好的映象源：
中科大映象源
deb bionic main restricted universe multiverse
deb-src bionic main restricted universe multiverse
deb bionic-updates main restricted universe multiverse
deb-src bionic-updates main restricted universe multiverse
deb bionic-backports main restricted universe multiverse
deb-src bionic-backports main restricted universe multiverse
deb bionic-security main restricted universe multiverse
deb-src bionic-security main restricted universe multiverse
deb bionic-proposed main restricted universe multiverse
deb-src bionic-proposed main restricted universe multiverse
清華映象源
deb bionic main restricted universe multiverse
deb-src bionic main restricted universe multiverse
deb bionic-updates main restricted universe multiverse
deb-src bionic-updates main restricted universe multiverse
deb bionic-backports main restricted universe multiverse
deb-src bionic-backports main restricted universe multiverse
deb bionic-security main restricted universe multiverse
deb-src bionic-security main restricted universe multiverse
deb bionic-proposed main restricted universe multiverse
deb-src bionic-proposed main restricted universe multiverse
163映象源
deb bionic main restricted universe multiverse
deb bionic-security main restricted universe multiverse
deb bionic-updates main restricted universe multiverse
deb bionic-proposed main restricted universe multiverse
deb bionic-backports main restricted universe multiverse
deb-src bionic main restricted universe multiverse
deb-src bionic-security main restricted universe multiverse
deb-src bionic-updates main restricted universe multiverse
deb-src bionic-proposed main restricted universe multiverse
deb-src bionic-backports main restricted universe multiverse
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