更換源
沒有更換源，直接用sudo apt install xxx會十分的慢，因爲它是從國外的服務器中下載，所以我選擇換用國內的源，體驗一下飛一般的下載的快樂。
這是原博==
其實就是那麼幾步，首先
#備份源文件列表
sudo cp /etc/apt/sources.list /etc/apt/sources.list_backup #其實後面那個文件名稱可以隨便填，只是留個副本
然後打開源文件列表（我用的是vim，原博用的是別的文檔操作的軟件）
sudo vim /etc/apt/sources.list
在文件頭部插入：
# 阿里源
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
也可以換別的源，原博給了好多源，反正我用的是阿里源，所以這裏只寫阿里源。
最後刷新列表。
sudo apt-get update
sudo apt-get upgrade
sudo apt-get install build-essential
就成功了。