Ubuntu的源其實是在美國的，在中國獲取當然速度有點慢，因此通過換國內的源能夠有效的加快下載軟件的速度。
更換源有兩種方式，本人推薦第二種。
系統設置修改
如圖1，點擊右上角圖標，再點擊System Setting，進入系統設置頁面。
如圖2，點擊Software&Updates，進入修改界面。
如圖3，點擊Download from更換源，點擊other，選擇China目錄下的即可，推薦網易，清華的源。選擇完畢，點擊Close。
源文件修改
網易16.04的源
deb http://mirrors.163.com/ubuntu/ xenial main restricted universe multiverse
deb http://mirrors.163.com/ubuntu/ xenial-security main restricted universe multiverse
deb http://mirrors.163.com/ubuntu/ xenial-updates main restricted universe multiverse
deb http://mirrors.163.com/ubuntu/ xenial-proposed main restricted universe multiverse
deb http://mirrors.163.com/ubuntu/ xenial-backports main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ xenial main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ xenial-security main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ xenial-updates main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ xenial-proposed main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ xenial-backports main restricted universe multiverse
清華16.04的源
deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ bionic main restricted universe multiverse
deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ bionic main restricted universe multiverse
deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ bionic-updates main restricted universe multiverse
deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ bionic-updates main restricted universe multiverse
deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ bionic-backports main restricted universe multiverse
deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ bionic-backports main restricted universe multiverse
deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ bionic-security main restricted universe multiverse
deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ bionic-security main restricted universe multiverse
deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ bionic-proposed main restricted universe multiverse
deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ bionic-proposed main restricted universe multiverse
#進入源文件目錄創建新的源文件
cd /etc/apt/
sudo gedit sources.list.bak1
複製上面的任意一個源，粘貼入文件，並保存。
mv sources.list sources.list.bak2
mv sources.list.bak1 sources.list
#進行更新
sudo apt-get update
常見問題
問題1：
進行update操作會遇到如下問題：
W: An error occurred during the signature verification. The repository is not updated and the previous index files will be used. GPG error: http://dl.google.com/linux/chrome/deb stable Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 78BD65473CB3BD13
W: Failed to fetch http://dl.google.com/linux/chrome/deb/dists/stable/Release.gpg The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 78BD65473CB3BD13
遇到如上的報錯，其實是GPG錯誤，簽名無法驗證，我們所要做的，就是獲取系統中的這個公鑰，從信息中獲取密鑰號。在上述信息中，密鑰號爲78BD65473CB3BD13。該密鑰可通過以下方式使用：
sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys 78BD65473CB3BD13
在添加密鑰後，再次運行更新就沒有問題了，如圖4：
問題2：
E: Problem executing scripts APT::Update::Post-Invoke-Success 'if /usr/bin/test -w /var/cache/app-info -a -e /usr/bin/appstreamcli; then appstreamcli refresh > /dev/null; fi'
E: Sub-process returned an error code
這個問題只需要依次執行以下代碼即可：
sudo pkill -KILL appstreamcli
wget -P /tmp https://launchpad.net/ubuntu/+archive/primary/+files/appstream_0.9.4-1ubuntu1_amd64.deb https://launchpad.net/ubuntu/+archive/primary/+files/libappstream3_0.9.4-1ubuntu1_amd64.deb
sudo dpkg -i /tmp/appstream_0.9.4-1ubuntu1_amd64.deb /tmp/libappstream3_0.9.4-1ubuntu1_amd64.deb
之後update就可以執行完成。