如何在Docker Ubuntu镜像上安装git？

Question

我有一个简单的docker文件

FROM ubuntu:18.04
COPY . /usr/src/app/
COPY docker_files/.bash_aliases /root/

$ docker build -t dock .
Sending build context to Docker daemon  146.9kB
Step 1/3 : FROM ubuntu:18.04
 ---> 94e814e2efa8
Step 2/3 : COPY . /usr/src/app/
 ---> bf79eb6c42c1
Step 3/3 : COPY docker_files/.bash_aliases /root/
 ---> aedc97d5ee8b
Successfully built aedc97d5ee8b
Successfully tagged dock:latest

我可以使用它：

$ docker run -it dock
bash: git: command not found
root@6a6bec871690:/# ls usr/src/app/
Dockerfile  Gemfile  Gemfile.lock  README.md  docker_files  go  ...
root@6a6bec871690:/# 

如您所见，我的文件已复制，并且为root创建了别名。但是找不到git（因此err msg）并且未安装。
鉴于我在下面的尝试失败，如何安装它？

root@753b573271d5:/# git
bash: git: command not found
root@753b573271d5:/# apt-get install git
Reading package lists... Done
Building dependency tree       
Reading state information... Done
E: Unable to locate package git
root@753b573271d5:/# sudo apt-get install git 
bash: sudo: command not found

Answer 1

这个 Dockerfile 对我有用

FROM ubuntu:18.04
RUN apt update
RUN apt install -y git

容器内部

$ which git
/usr/bin/git

Answer 2

apt-get update

apt-get install git