使用基于 Ubuntu 的 Docker 时，如果需要 apt-get，默认的 ubuntu 源可能会非常慢，因此推荐更换为国内源，如阿里云等.

在 Dockerfile 文件更换阿里云源：
如：

FROM ubuntu:16.04

# Ali apt-get source.list
RUN mv /etc/apt/sources.list /etc/apt/sources.list.bak && \
    echo "deb-src http://archive.ubuntu.com/ubuntu xenial main restricted" >/etc/apt/sources.list && \
    echo "deb http://mirrors.aliyun.com/ubuntu/ xenial main restricted" >>/etc/apt/sources.list && \
    echo "deb-src http://mirrors.aliyun.com/ubuntu/ xenial main restricted multiverse universe" >>/etc/apt/sources.list && \
    echo "deb http://mirrors.aliyun.com/ubuntu/ xenial-updates main restricted" >>/etc/apt/sources.list && \
    echo "deb-src http://mirrors.aliyun.com/ubuntu/ xenial-updates main restricted multiverse universe" >>/etc/apt/sources.list && \
    echo "deb http://mirrors.aliyun.com/ubuntu/ xenial universe" >>/etc/apt/sources.list && \
    echo "deb http://mirrors.aliyun.com/ubuntu/ xenial-updates universe" >>/etc/apt/sources.list && \
    echo "deb http://mirrors.aliyun.com/ubuntu/ xenial multiverse" >>/etc/apt/sources.list && \
    echo "deb http://mirrors.aliyun.com/ubuntu/ xenial-updates multiverse" >>/etc/apt/sources.list && \
    echo "deb http://mirrors.aliyun.com/ubuntu/ xenial-backports main restricted universe multiverse" >>/etc/apt/sources.list && \
    echo "deb-src http://mirrors.aliyun.com/ubuntu/ xenial-backports main restricted universe multiverse" >>/etc/apt/sources.list && \
    echo "deb http://archive.canonical.com/ubuntu xenial partner" >>/etc/apt/sources.list && \
    echo "deb-src http://archive.canonical.com/ubuntu xenial partner" >>/etc/apt/sources.list && \
    echo "deb http://mirrors.aliyun.com/ubuntu/ xenial-security main restricted" >>/etc/apt/sources.list && \
    echo "deb-src http://mirrors.aliyun.com/ubuntu/ xenial-security main restricted multiverse universe" >>/etc/apt/sources.list && \
    echo "deb http://mirrors.aliyun.com/ubuntu/ xenial-security universe" >>/etc/apt/sources.list && \
    echo "deb http://mirrors.aliyun.com/ubuntu/ xenial-security multiverse" >>/etc/apt/sources.list

RUN apt-get update \
    && apt-get install -y --no-install-recommends \
        ca-certificates \
        vim \
        python \
        libopencv-dev \
        python-pip \
    && rm -rf /var/lib/apt/lists/*

RUN pip install --upgrade pip \
    numpy \
    pymongo \
    opencv-python

Ubuntu20.04:

FROM ubuntu:20.04

RUN mv /etc/apt/sources.list /etc/apt/sources.list.bak && \
    echo "deb http://mirrors.aliyun.com/ubuntu/ focal-updates main restricted" >/etc/apt/sources.list && \
    echo "deb http://mirrors.aliyun.com/ubuntu/ focal universe" >/etc/apt/sources.list && \
    echo "deb http://mirrors.aliyun.com/ubuntu/ focal-updates universe" >/etc/apt/sources.list && \
    echo "deb http://mirrors.aliyun.com/ubuntu/ focal multiverse" >/etc/apt/sources.list && \
    echo "deb http://mirrors.aliyun.com/ubuntu/ focal-updates multiverse" >/etc/apt/sources.list && \
    echo "deb http://mirrors.aliyun.com/ubuntu/ focal-backports main restricted universe multiverse" >/etc/apt/sources.list && \
    echo "deb http://mirrors.aliyun.com/ubuntu/ focal-security main restricted" >/etc/apt/sources.list && \
    echo "deb http://mirrors.aliyun.com/ubuntu/ focal-security universe" >/etc/apt/sources.list && \
    echo "deb http://mirrors.aliyun.com/ubuntu/ focal-security multiverse" >/etc/apt/sources.list