Docker中的CMD和ENTRYPOINT区别

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1.CMD

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The main purpose of a CMD is to provide defaults for an executing container.
CMD在容器运行的时候提供一些命令及参数，用法如下：
1.CMD ["executable","param1","param2"] (exec form, this is the preferred form)
2.CMD ["param1","param2"] (as default parameters to ENTRYPOINT)
3.CMD command param1 param2 (shell form)

如：CMD ["/bin/echo", "this is a echo test"], docker run: docker run imagename后输出: this is a echo test

docker run命令如果指定了参数会把CMD里的参数覆盖
如：docker run imagename /bin/bash, 就不会输出：this is a echo test，因为CMD命令被”/bin/bash”覆盖了

2.ENTRYPOINT

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An ENTRYPOINT allows you to configure a container that will run as an executable.
它可以让你的容器功能表现得像一个可执行程序一样。
1.ENTRYPOINT ["executable", "param1", "param2"] (exec form, preferred)
2.ENTRYPOINT command param1 param2 (shell form)

如：ENTRYPOINT ["/bin/echo"]，那么build出来的镜像以后的容器功能就像一个/bin/echo程序
docker run -it imagename "this is a test"就等于/bin/echo "this is a test"

注：
1.ENTRYPOINT有两种写法，第二种(shell form)会屏蔽掉docker run时后面加的命令和CMD里的参数。
2.Dockerfile中同时有ENTRYPOINT和CMD，是将CMD当参数传入ENTRYPOINT

3.Demo

Dockefile

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FROM debian:latest
ADD entypoint.sh /entypoint.sh
ADD run.sh /run.sh
RUN chmod 755 /*.sh
ENTRYPOINT ["/entypoint.sh"]
CMD [/run.sh]

run.sh

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#!/bin/bash
echo "=> do run.sh!"

entypoint.sh

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#!/bin/bash
echo "=> do entypoint.sh!"
echo "=> Quoted Values: $*"

Biuld && Run

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sudo docker build -t debian:test .
sudo docker run --rm debian:test

1.当ENTRYPOINT ["/entypoint.sh"]和CMD ["/run.sh"]，输出结果：

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=> do entypoint.sh!
=> Quoted Values: /run.sh

2.当ENTRYPOINT /entypoint.sh和CMD ["/run.sh"]，输出结果：

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=> do entypoint.sh!
=> Quoted Values:

3.当ENTRYPOINT ["/entypoint.sh"]和CMD /run.sh，输出结果：

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=> do entypoint.sh!
=> Quoted Values: /bin/sh -c /run.sh