事情是起因就是这个ubantu18.04里没有ifconfig命令。
需要sudo apt-get install net-tools。
执行这个命令后，发现net-tools没办法安装，需要sudo apt update。
这个命令也报错，因为/etc/aptsources.list里的网址国内连不到，将文件的内容全部替换成下面的内容就行。
deb http://mirrors.aliyun.com/ubuntu/ trusty main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ trusty-security main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ trusty-updates main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ trusty-proposed main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ trusty-backports main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ trusty main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ trusty-security main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ trusty-updates main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ trusty-proposed main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ trusty-backports main restricted universe multiverse
#centos源（放心使用）：
deb http://centos.bitcomm.cn/ubuntu trusty main restricted universe multiverse
deb http://centos.bitcomm.cn/ubuntu trusty-security main restricted universe multiverse
deb http://centos.bitcomm.cn/ubuntu trusty-updates main restricted universe multiverse
deb http://centos.bitcomm.cn/ubuntu trusty-backports main restricted universe multiverse
deb http://centos.bitcomm.cn/ubuntu trusty-proposed main restricted universe multiverse
deb-src http://centos.bitcomm.cn/ubuntu trusty main restricted universe multiverse
deb-src http://centos.bitcomm.cn/ubuntu trusty-security main restricted universe multiverse
deb-src http://centos.bitcomm.cn/ubuntu trusty-updates main restricted universe multiverse
deb-src http://centos.bitcomm.cn/ubuntu trusty-backports main restricted universe multiverse
deb-src http://centos.bitcomm.cn/ubuntu trusty-proposed main restricted universe multiverse
到这里，又出现新的问题，因为用的是虚拟机，不能直接复制过去，手敲太麻烦了，想直接从电脑里复制过去需要安装vmwareTools。vmware-tools安装方法
直接拖进去还需要 sudo nautilus。
好的，到这里问题算是解决完了。
再次sudo apt update
sudo apt-get install net-tools
ifconfig就找到了。