Dockerfile 由一行行命令語(yǔ)句組成，并且支持以 # 開(kāi)頭的注釋行。
一般的，Dockerfile 分為四部分：基礎(chǔ)鏡像信息、維護(hù)者信息、鏡像操作指令和容器啟動(dòng)時(shí)執(zhí)行指令。
例如
# This dockerfile uses the ubuntu image
# VERSION 2 - EDITION 1
# Author: docker_user
# Command format: Instruction [arguments / command] ..
# Base image to use, this must be set as the first line
FROM ubuntu
# Maintainer: docker_user <docker_user at email.com> (@docker_user)
MAINTAINER docker_user docker_user@email.com
# Commands to update the image
RUN echo "deb http://archive.ubuntu.com/ubuntu/ raring main universe" >> /etc/apt/sources.list
RUN apt-get update && apt-get install -y nginx
RUN echo "\ndaemon off;" >> /etc/nginx/nginx.conf
# Commands when creating a new container
CMD /usr/sbin/nginx其中，一開(kāi)始必須指明所基于的鏡像名稱，接下來(lái)推薦說(shuō)明維護(hù)者信息。
后面則是鏡像操作指令，例如 RUN 指令，RUN 指令將對(duì)鏡像執(zhí)行跟隨的命令。每運(yùn)行一條 RUN 指令，鏡像添加新的一層，并提交。
最后是 CMD 指令，來(lái)指定運(yùn)行容器時(shí)的操作命令。
下面是一個(gè)更復(fù)雜的例子
# Nginx
#
# VERSION 0.0.1
FROM ubuntu
MAINTAINER Victor Vieux <victor@docker.com>
RUN apt-get update && apt-get install -y inotify-tools nginx apache2 openssh-server
# Firefox over VNC
#
# VERSION 0.3
FROM ubuntu
# Install vnc, xvfb in order to create a 'fake' display and firefox
RUN apt-get update && apt-get install -y x11vnc xvfb firefox
RUN mkdir /.vnc
# Setup a password
RUN x11vnc -storepasswd 1234 ~/.vnc/passwd
# Autostart firefox (might not be the best way, but it does the trick)
RUN bash -c 'echo "firefox" >> /.bashrc'
EXPOSE 5900
CMD ["x11vnc", "-forever", "-usepw", "-create"]
# Multiple images example
#
# VERSION 0.1
FROM ubuntu
RUN echo foo > bar
# Will output something like ===> 907ad6c2736f
FROM ubuntu
RUN echo moo > oink
# Will output something like ===> 695d7793cbe4
# You?ll now have two images, 907ad6c2736f with /bar, and 695d7793cbe4 with
# /oink.
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