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Dockerfile的CMD與ENTRYPOINT的區(qū)別

更新時間：2024年12月16日 11:00:45 作者：芝麻\n

CMD和ENTRYPOINT的區(qū)別在于CMD提供默認的執(zhí)行指令,而ENTRYPOINT定義容器啟動時運行的命令,下面就來詳細的介紹一下這兩者的區(qū)別,具有一定的參考價值,感興趣的可以了解一下

CMD和ENTRYPOINT

我們先來試一下構(gòu)建以下這個Dockerfile，并運行

FROM centos

CMD ["ls","-a"]

構(gòu)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

運行

[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

可以發(fā)現(xiàn)，進入容器之后，就執(zhí)行了ls -a命令

我們嘗試一下在啟動的時候加入一些參數(shù)

[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.

我們發(fā)現(xiàn)容器并沒有執(zhí)行ls -al，而是直接報錯了

其實這就是CMD的特性，當我在啟動容器的時候添加了一個CMD后

鏡像中定義的CMD就被覆蓋掉了

單獨的-l當然會報錯了

我們來看一下使用ENTRYPOINT會怎么樣

修改Dockerfile

FROM centos

ENTRYPOINT ["ls","-a"]

重新構(gòu)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

運行容器

[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

可以發(fā)現(xiàn)，容器執(zhí)行的是ls -al，-l指令被追加給了ENTRYPOINT定義的語句

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