CMD和ENTRYPOINT

CMD：指定这个容器启动的时候需要执行的命令，但是只有最后一个CMD会生效
ENTRYPOINT：指定这个容器启动的时候需要执行的命令，且可以追加命令

测试CMD
1、编写使用CMD的dockerfile文件
举例：测试制作centos镜像时，输出ls -a的全部目录

FROM centos
CMD ["ls","-a"]

2、构建镜像

[root@liuyang dockerfile]# docker build -f first_dockerfile_cmd  -t centos_liuyang:1.4  .

#输出日志

Sending build context to Docker daemon  3.072kB
Step 1/2 : FROM centos
 ---> 300e315adb2f
Step 2/2 : CMD ["ls","-a"]
 ---> Running in 2a3b27d08525
Removing intermediate container 2a3b27d08525
 ---> 67b2d498c93c
Successfully built 67b2d498c93c
Successfully tagged centos_liuyang:1.4
[root@liuyang dockerfile]# docker images
REPOSITORY              TAG       IMAGE ID       CREATED          SIZE
centos_liuyang          1.4       67b2d498c93c   7 seconds ago    209MB
centos_dockerfile       1.3       2900faf7489f   16 minutes ago   291MB
centos_dockerfile       1.1       ff7532b27bf0   31 minutes ago   291MB
centos_dockerfile       1.2       316bfc73c556   31 minutes ago   291MB
liuyang_centos/centos   1.0       6bb3a414dd02   5 hours ago      209MB
centos                  1.2       c7755e562e14   2 days ago       209MB
mysql                   5.7       a70d36bc331a   7 weeks ago      449MB
tomcat                  latest    040bdb29ab37   2 months ago     649MB
nginx                   latest    f6d0b4767a6c   2 months ago     133MB
centos                  latest    300e315adb2f   3 months ago     209MB

3、查看镜像，并启动容器，查看效果（是否生成了centos 的ls -a，也就是CMD指令）

[root@liuyang dockerfile]# docker run -it 67b2d498c93c
.   .dockerenv  dev  home  lib64       media  opt   root  sbin  sys  usr
..  bin         etc  lib   lost+found  mnt    proc  run   srv   tmp  var

已生效！

此时我想在指令ls -a 后面追加l 变成ls -al ：

[root@liuyang dockerfile]# docker run -it 67b2d498c93c -l
docker: Error response from daemon: OCI runtime create failed: container_linux.go:349: starting container process caused "exec: \"-l\": executable file not found in $PATH": unknown.
ERRO[0000] error waiting for container: context canceled
[root@liuyang dockerfile]#

发现不行，必须写全代码：

[root@liuyang dockerfile]# docker run -it 67b2d498c93c  ls -al
total 56
drwxr-xr-x   1 root root 4096 Mar 14 14:14 .
drwxr-xr-x   1 root root 4096 Mar 14 14:14 ..
-rwxr-xr-x   1 root root    0 Mar 14 14:14 .dockerenv
lrwxrwxrwx   1 root root    7 Nov  3 15:22 bin -> usr/bin
drwxr-xr-x   5 root root  360 Mar 14 14:14 dev
drwxr-xr-x   1 root root 4096 Mar 14 14:14 etc
drwxr-xr-x   2 root root 4096 Nov  3 15:22 home
lrwxrwxrwx   1 root root    7 Nov  3 15:22 lib -> usr/lib
lrwxrwxrwx   1 root root    9 Nov  3 15:22 lib64 -> usr/lib64
drwx------   2 root root 4096 Dec  4 17:37 lost+found
drwxr-xr-x   2 root root 4096 Nov  3 15:22 media
drwxr-xr-x   2 root root 4096 Nov  3 15:22 mnt
drwxr-xr-x   2 root root 4096 Nov  3 15:22 opt
dr-xr-xr-x 145 root root    0 Mar 14 14:14 proc
dr-xr-x---   2 root root 4096 Dec  4 17:37 root
drwxr-xr-x  11 root root 4096 Dec  4 17:37 run
lrwxrwxrwx   1 root root    8 Nov  3 15:22 sbin -> usr/sbin
drwxr-xr-x   2 root root 4096 Nov  3 15:22 srv
dr-xr-xr-x  13 root root    0 Mar  1 05:43 sys
drwxrwxrwt   7 root root 4096 Dec  4 17:37 tmp
drwxr-xr-x  12 root root 4096 Dec  4 17:37 usr
drwxr-xr-x  20 root root 4096 Dec  4 17:37 var
[root@liuyang dockerfile]#

现在我们试一试ENTRYPOINT：
1、编写使用ENTRYPOINT的dockerfile文件
举例：测试制作centos镜像时，输出ls -a的全部目录

FROM centos
ENTRYPOINT ["ls","-a"]

2、构建镜像

[root@liuyang dockerfile]# docker build -f first_dockerfile_ENTRYPOINT  -t centos_liuyang:1.6 .

3、查看镜像，并启动容

[root@liuyang dockerfile]# docker run -it 2c0580c11880
.   .dockerenv  dev  home  lib64       media  opt   root  sbin  sys  usr
..  bin         etc  lib   lost+found  mnt    proc  run   srv   tmp  var
器，查看效果（是否生成了centos 的ls -a）

4、此时我想在指令ls -a 后面追加l 变成ls -al ：

[root@liuyang dockerfile]# docker run -it 2c0580c11880 -l
total 56
drwxr-xr-x   1 root root 4096 Mar 14 14:16 .
drwxr-xr-x   1 root root 4096 Mar 14 14:16 ..
-rwxr-xr-x   1 root root    0 Mar 14 14:16 .dockerenv
lrwxrwxrwx   1 root root    7 Nov  3 15:22 bin -> usr/bin
drwxr-xr-x   5 root root  360 Mar 14 14:16 dev
drwxr-xr-x   1 root root 4096 Mar 14 14:16 etc
drwxr-xr-x   2 root root 4096 Nov  3 15:22 home
lrwxrwxrwx   1 root root    7 Nov  3 15:22 lib -> usr/lib
lrwxrwxrwx   1 root root    9 Nov  3 15:22 lib64 -> usr/lib64
drwx------   2 root root 4096 Dec  4 17:37 lost+found
drwxr-xr-x   2 root root 4096 Nov  3 15:22 media
drwxr-xr-x   2 root root 4096 Nov  3 15:22 mnt
drwxr-xr-x   2 root root 4096 Nov  3 15:22 opt
dr-xr-xr-x 144 root root    0 Mar 14 14:16 proc
dr-xr-x---   2 root root 4096 Dec  4 17:37 root
drwxr-xr-x  11 root root 4096 Dec  4 17:37 run
lrwxrwxrwx   1 root root    8 Nov  3 15:22 sbin -> usr/sbin
drwxr-xr-x   2 root root 4096 Nov  3 15:22 srv
dr-xr-xr-x  13 root root    0 Mar  1 05:43 sys
drwxrwxrwt   7 root root 4096 Dec  4 17:37 tmp
drwxr-xr-x  12 root root 4096 Dec  4 17:37 usr
drwxr-xr-x  20 root root 4096 Dec  4 17:37 var
[root@liuyang dockerfile]#

生效！与CMD的区别显而易见，ENTRYPOINT 可以直接在run 后面追加 代码！