Dockerfile的CMD与ENTRYPOINT的区别
作者：芝麻\n
CMD和ENTRYPOINT的区别在于CMD提供默认的执行指令,而ENTRYPOINT定义容器启动时运行的命令,下面就来详细的介绍一下这两者的区别,具有一定的参考价值,感兴趣的可以了解一下
CMD和ENTRYPOINT
我们先来试一下构建以下这个Dockerfile，并运行
FROM centos CMD ["ls","-a"]
构建
[root@zhima lizhi]# docker build -t mycentos . Sending build context to Docker daemon 17.92kB Step 1/2 : FROM centos ---> 5d0da3dc9764 Step 2/2 : CMD ["ls","-a"] ---> Running in a1e70a05d8dd Removing intermediate container a1e70a05d8dd ---> 00433fd4c299 Successfully built 00433fd4c299 Successfully tagged mycentos:latest
运行
[root@zhima lizhi]# docker run -it --name "centos1" mycentos . .dockerenv dev home lib64 media opt root sbin sys usr .. bin etc lib lost+found mnt proc run srv tmp var
可以发现，进入容器之后，就执行了ls -a命令
我们尝试一下在启动的时候加入一些参数
[root@zhima lizhi]# docker run -it --name "centos2" mycentos -l docker: Error response from daemon: OCI runtime create failed: container_linux.go:380: starting container process caused: exec: "-l": executable file not found in $PATH: unknown.
我们发现容器并没有执行ls -al，而是直接报错了
其实这就是CMD的特性，当我在启动容器的时候添加了一个CMD后
镜像中定义的CMD就被覆盖掉了
单独的-l当然会报错了
我们来看一下使用ENTRYPOINT会怎么样
修改Dockerfile
FROM centos ENTRYPOINT ["ls","-a"]
重新构建
[root@zhima lizhi]# docker build -t mycentos . Sending build context to Docker daemon 17.92kB Step 1/2 : FROM centos ---> 5d0da3dc9764 Step 2/2 : ENTRYPOINT ["ls","-a"] ---> Running in 22ef40dea625 Removing intermediate container 22ef40dea625 ---> 73a3d51b4d84 Successfully built 73a3d51b4d84 Successfully tagged mycentos:latest
运行容器
[root@zhima lizhi]# docker run -it --name "centos1" mycentos -l total 56 drwxr-xr-x 1 root root 4096 Jul 14 08:52 . drwxr-xr-x 1 root root 4096 Jul 14 08:52 .. -rwxr-xr-x 1 root root 0 Jul 14 08:52 .dockerenv lrwxrwxrwx 1 root root 7 Nov 3 2020 bin -> usr/bin drwxr-xr-x 5 root root 360 Jul 14 08:52 dev drwxr-xr-x 1 root root 4096 Jul 14 08:52 etc drwxr-xr-x 2 root root 4096 Nov 3 2020 home lrwxrwxrwx 1 root root 7 Nov 3 2020 lib -> usr/lib lrwxrwxrwx 1 root root 9 Nov 3 2020 lib64 -> usr/lib64 drwx------ 2 root root 4096 Sep 15 2021 lost+found drwxr-xr-x 2 root root 4096 Nov 3 2020 media drwxr-xr-x 2 root root 4096 Nov 3 2020 mnt drwxr-xr-x 2 root root 4096 Nov 3 2020 opt dr-xr-xr-x 191 root root 0 Jul 14 08:52 proc dr-xr-x--- 2 root root 4096 Sep 15 2021 root drwxr-xr-x 11 root root 4096 Sep 15 2021 run lrwxrwxrwx 1 root root 8 Nov 3 2020 sbin -> usr/sbin drwxr-xr-x 2 root root 4096 Nov 3 2020 srv dr-xr-xr-x 13 root root 0 Jan 29 10:27 sys drwxrwxrwt 7 root root 4096 Sep 15 2021 tmp drwxr-xr-x 12 root root 4096 Sep 15 2021 usr drwxr-xr-x 20 root root 4096 Sep 15 2021 var
可以发现，容器执行的是ls -al，-l指令被追加给了ENTRYPOINT定义的语句
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