CMD/ENTRYPOINT都是指定一个容器启动时要运行的命令。但是CMD会覆盖前面的参数，而ENTRYPONT会追加组合原来的参数。
Dockfile中可以有多个CMD指令，但只有最后一个生效。
另外，CMD会被docker run之后的参数替换，举例说明：
计算
安全
数据库
网络和加速
企业服务
[root@t-docker chenzx]# docker run -it -p 8080:8080 tomcat
01-Sep-2018 12:52:39.808 INFO [localhost-startStop-1] org.apache.catalina.startup.HostConfig.deployDirectory Deploying web application directory [/usr/local/tomcat/webapps/manager]
01-Sep-2018 12:52:39.822 INFO [localhost-startStop-1] org.apache.catalina.startup.HostConfig.deployDirectory Deployment of web application directory [/usr/local/tomcat/webapps/manager] has finished in [14] ms
01-Sep-2018 12:52:39.827 INFO [main] org.apache.coyote.AbstractProtocol.start Starting ProtocolHandler ["http-nio-8080"]
01-Sep-2018 12:52:39.834 INFO [main] org.apache.coyote.AbstractProtocol.start Starting ProtocolHandler ["ajp-nio-8009"]
01-Sep-2018 12:52:39.836 INFO [main] org.apache.catalina.startup.Catalina.start Server startup in 510 ms
[root@t-docker chenzx]# docker run -it -p 8080:8080 tomcat ls -l
total 120
-rw-r----- 1 root root 19533 Aug 12 08:23 BUILDING.txt
-rw-r----- 1 root root 6090 Aug 12 08:23 CONTRIBUTING.md
-rw-r----- 1 root root 57092 Aug 12 08:23 LICENSE
-rw-r----- 1 root root 1726 Aug 12 08:23 NOTICE
-rw-r----- 1 root root 3255 Aug 12 08:23 README.md
-rw-r----- 1 root root 7140 Aug 12 08:23 RELEASE-NOTES
-rw-r----- 1 root root 16262 Aug 12 08:23 RUNNING.txt
drwxr-x--- 2 root root 313 Aug 23 00:47 bin
drwx--S--- 2 root root 238 Aug 12 08:23 conf
drwxr-sr-x 3 root staff 19 Aug 23 00:47 include
drwxr-x--- 2 root root 4096 Aug 23 00:47 lib
drwxr-x--- 2 root root 6 Aug 12 08:20 logs
drwxr-sr-x 3 root staff 151 Aug 23 00:47 native-jni-lib
drwxr-x--- 2 root root 30 Aug 23 00:47 temp
drwxr-x--- 7 root root 81 Aug 12 08:21 webapps
drwxr-x--- 2 root root 6 Aug 12 08:20 work
通过上面可以看出，最后面的ls -l覆盖了启动tomcat的操作。这就是CMD会被docker run之后的参数替换。
docker run之后的参数会被当做参数传递给ENTRYPOINT,之后形成新的命令组合。
[root@t-docker CMD]# cat Dockerfile
from centos
RUN yum -y install curl
CMD ["curl","-s","http://ip.cn"]
[root@t-docker CMD]# docker build -f Dockerfile -t myip .
Sending build context to Docker daemon 2.048kB
Step 1/3 : from centos
---> 5182e96772bf
Step 2/3 : RUN yum -y install curl
---> Running in aa5e5f0a8597
Loaded plugins: fastestmirror, ovl
Determining fastest mirrors
* base: mirrors.huaweicloud.com
* extras: mirrors.huaweicloud.com
* updates: mirrors.neusoft.edu.cn
Package curl-7.29.0-46.el7.x86_64 already installed and latest version
Nothing to do
Removing intermediate container aa5e5f0a8597
---> a35f6ad9700f
Step 3/3 : CMD ["curl","-s","http://ip.cn"]
---> Running in f59369e2a7db
Removing intermediate container f59369e2a7db
---> ecf0b349d6a1
Successfully built ecf0b349d6a1
Successfully tagged myip:latest
[root@t-docker CMD]# docker images
REPOSITORY TAG IMAGE ID CREATED SIZE
myip latest ecf0b349d6a1 About a minute ago 293MB
mycentos 1.3 0c868c56748b 3 hours ago 442MB
chenzx/centos latest a37b96c1c7a7 35 hours ago 200MB
chenzx/tomcat02 1.2 24c3d89d4d04 2 days ago 463MB
tomcat latest 690cb3b9c7d1 9 days ago 463MB
centos latest 5182e96772bf 3 weeks ago 200MB
[root@t-docker CMD]#
[root@t-docker CMD]# docker run -it myip
当前 IP：223.72.205.1 来自：北京市 移动
[root@t-docker CMD]# curl -s http://ip.cn
当前 IP：223.72.205.1 来自：北京市 移动
[root@t-docker CMD]#
[root@t-docker CMD]# curl -s -i http://ip.cn
HTTP/1.1 200 OK
Date: Sat, 01 Sep 2018 13:19:24 GMT
Content-Type: text/html; charset=UTF-8
Transfer-Encoding: chunked
Connection: keep-alive
Set-Cookie: __cfduid=defee6872152b4b29d3a55de1eb3f219d1535807964; expires=Sun, 01-Sep-19 13:19:24 GMT; path=/; domain=.ip.cn; HttpOnly
Server: cloudflare
CF-RAY: 45380742316fb236-HKG
当前 IP：223.72.205.1 来自：北京市 移动
[root@t-docker CMD]# docker run myip
当前 IP：223.72.205.1 来自：北京市 移动
[root@t-docker CMD]# docker run myip -i #可以看到报错了
docker: Error response from daemon: OCI runtime create failed: container_linux.go:348: starting container process caused "exec: \"-i\": executable file not found in $PATH": unknown.
ERRO[0000] error waiting for container: context canceled
我们可以看到出现了一个可执行文件找不到的报错： executable file not found in $PATH。之前我们说过， 跟在镜像名后面的是command，运行时会替换CMD的默认值。
因此，这里面的-i替换了原来的CMD参数，而不是在原来的curl -s http://ip.cn后面。而-i根本就不是命令，所以自然找不到。
那我们如果希望加入-i参数，我们就必须重新完整的输入这个命令：
[root@t-docker CMD]# docker run myip curl -s http://ip.cn -i
HTTP/1.1 200 OK
Date: Sat, 01 Sep 2018 13:28:03 GMT
Content-Type: text/html; charset=UTF-8
Transfer-Encoding: chunked
Connection: keep-alive
Set-Cookie: __cfduid=d8b76a4d8c8ebb4bf69f97a92cc39216e1535808483; expires=Sun, 01-Sep-19 13:28:03 GMT; path=/; domain=.ip.cn; HttpOnly
Server: cloudflare
CF-RAY: 453813eed351b11c-HKG
当前 IP：223.72.205.1 来自：北京市 移动
[root@t-docker CMD]# cat Dockerfile2
from centos
RUN yum -y install curl
ENTRYPOINT ["curl","-s","http://ip.cn"]
[root@t-docker CMD]#
[root@t-docker CMD]# docker build -f Dockerfile2 -t myip2 .
Sending build context to Docker daemon 3.072kB
Step 1/3 : from centos
---> 5182e96772bf
Step 2/3 : RUN yum -y install curl
---> Using cache
---> a35f6ad9700f
Step 3/3 : ENTRYPOINT ["curl","-s","http://ip.cn"]
---> Running in 36f7f6639933
Removing intermediate container 36f7f6639933
---> b772af142e86
Successfully built b772af142e86
Successfully tagged myip2:latest
[root@t-docker CMD]# docker run -it myip2
当前 IP：223.72.205.1 来自：北京市 移动
[root@t-docker CMD]# docker run -it myip2 -i ##正确执行
HTTP/1.1 200 OK
Date: Sat, 01 Sep 2018 13:57:37 GMT
Content-Type: text/html; charset=UTF-8
Transfer-Encoding: chunked
Connection: keep-alive
Set-Cookie: __cfduid=ded1abdaf2b8375c2fb815f8d262e4c781535810257; expires=Sun, 01-Sep-19 13:57:37 GMT; path=/; domain=.ip.cn; HttpOnly
Server: cloudflare
CF-RAY: 45383f3c074bb20c-HKG
当前 IP：223.72.205.1 来自：北京市 移动
可见，ENTRYPOINT没有覆盖原参数，而是追加到原参数的后面。
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原文链接：http://blog.itpub.net/28916011/viewspace-2213396/
