Dockerfile的CMD與ENTRYPOINT的區(qū)別
CMD和ENTRYPOINT
我們先來試一下構建以下這個Dockerfile,并運行
FROM centos CMD ["ls","-a"]
構建
[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,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
[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,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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