21.CMD与ENTRYPOINT的区别

• CMD 指定这个容器启动的时候要运行的命令,只有最后一个会生效，可被替代
• ENTRYPOINT 指定这个容器启动的时候要运行的命令，可以追加命令

21.1. CMD测试

编写一个dockerfile文件dockerfile-cmd-centos，脚本如下

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

构建镜像

docker build -f dockerfile-cmd-centos -t cmd-centos .

使用cmd-centos 镜像，运行容器

docker run cmd-centos

输出结果如下：

[root@iZ8vb6lqqya4rvreq9ra6gZ dockerfile_test]# docker run cmd-centos
.
..
.dockerenv
bin
dev
etc
home
lib
lib64
lost+found
media
mnt
opt
proc
root
run
sbin
srv
sys
tmp
usr
var

再使用如下命令运行cmd-centos镜像

docker run cmd-centos -l

出现如下错误信息

[root@iZ8vb6lqqya4rvreq9ra6gZ dockerfile_test]# docker run cmd-centos -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.
ERRO[0000] error waiting for container: context canceled 
[root@iZ8vb6lqqya4rvreq9ra6gZ dockerfile_test]# 

21.2. ENTRYPOINT测试

编写一个dockerfile文件dockerfile-entrypoint-centos，脚本如下

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

构建镜像

docker build -f dockerfile-entrypoint-centos -t entrypoint-centos .

使用entrypoint-centos 镜像，运行容器

docker run entrypoint-centos

输出结果如下：

[root@iZ8vb6lqqya4rvreq9ra6gZ dockerfile_test]# docker run entrypoint-centos
.
..
.dockerenv
bin
dev
etc
home
lib
lib64
lost+found
media
mnt
opt
proc
root
run
sbin
srv
sys
tmp
usr
var

再使用如下命令运行entrypoint-centos镜像

docker run entrypoint-centos -l

输出如下信息

[root@iZ8vb6lqqya4rvreq9ra6gZ dockerfile_test]# docker run entrypoint-centos -l
total 56
drwxr-xr-x   1 root root 4096 Feb 27 15:12 .
drwxr-xr-x   1 root root 4096 Feb 27 15:12 ..
-rwxr-xr-x   1 root root    0 Feb 27 15:12 .dockerenv
lrwxrwxrwx   1 root root    7 Nov  3  2020 bin -> usr/bin
drwxr-xr-x   5 root root  340 Feb 27 15:12 dev
drwxr-xr-x   1 root root 4096 Feb 27 15:12 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 14:17 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 209 root root    0 Feb 27 15:12 proc
dr-xr-x---   2 root root 4096 Sep 15 14:17 root
drwxr-xr-x  11 root root 4096 Sep 15 14:17 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 Feb 27 15:12 sys
drwxrwxrwt   7 root root 4096 Sep 15 14:17 tmp
drwxr-xr-x  12 root root 4096 Sep 15 14:17 usr
drwxr-xr-x  20 root root 4096 Sep 15 14:17 var
[root@iZ8vb6lqqya4rvreq9ra6gZ dockerfile_test]# 

21.3. 区别

区别如下图：