【Docker】Dockerfile 之 ENTRYPOINT（三）

参考教程：https://docs.docker.com/engine/reference/builder/

环境

1. virtual box 6.1
2. centos 7.8
3. docker 19.03

ENTRYPOINT 的 shell 格式示例

You can specify a plain string for the ENTRYPOINT and it will execute in /bin/sh -c. This form will use shell processing to substitute shell environment variables, and will ignore any CMD or docker run command line arguments. To ensure that docker stop will signal any long running ENTRYPOINT executable correctly, you need to remember to start it with exec:
您可以为 ENTRYPOINT 指定一个纯字符串，它将在 /bin/sh -c 中执行。这种形式将使用外壳处理环境变量，并且将忽略任何 CMD 或 docker run 命令行参数。为了确保 docker stop 能够正确通知任何长期运行的 ENTRYPOINT 可执行文件，您需要记住要使用 exec 启动它：

FROM ubuntu
ENTRYPOINT exec top -b

When you run this image, you’ll see the single PID 1 process:
当运行这个镜像时，您会看到一个 PID 1 进程：

$ docker run -it --rm --name test top

Mem: 1704520K used, 352148K free, 0K shrd, 0K buff, 140368121167873K cached
CPU:   5% usr   0% sys   0% nic  94% idle   0% io   0% irq   0% sirq
Load average: 0.08 0.03 0.05 2/98 6
  PID  PPID USER     STAT   VSZ %VSZ %CPU COMMAND
    1     0 root     R     3164   0%   0% top -b

Which exits cleanly on docker stop:
使用 docker stop 可以完全退出：

$ /usr/bin/time docker stop test

test
real	0m 0.20s
user	0m 0.02s
sys	0m 0.04s

If you forget to add exec to the beginning of your ENTRYPOINT:
如果您忘记在 ENTRYPOINT 的开头添加 exec：

FROM ubuntu
ENTRYPOINT top -b
CMD --ignored-param1

You can then run it (giving it a name for the next step):
然后可以运行它（为下一步命名）：

$ docker run -it --name test top --ignored-param2

Mem: 1704184K used, 352484K free, 0K shrd, 0K buff, 140621524238337K cached
CPU:   9% usr   2% sys   0% nic  88% idle   0% io   0% irq   0% sirq
Load average: 0.01 0.02 0.05 2/101 7
  PID  PPID USER     STAT   VSZ %VSZ %CPU COMMAND
    1     0 root     S     3168   0%   0% /bin/sh -c top -b cmd cmd2
    7     1 root     R     3164   0%   0% top -b

You can see from the output of top that the specified ENTRYPOINT is not PID 1.
从 top 的输出中可以看到，指定的 ENTRYPOINT 不是 PID 1。

If you then run docker stop test, the container will not exit cleanly - the stop command will be forced to send a SIGKILL after the timeout:
如果随后运行 docker stop test，则容器将不会干净退出。超时后，将强制执行 stop 命令发送 SIGKILL：

$ docker exec -it test ps aux

PID   USER     COMMAND
    1 root     /bin/sh -c top -b cmd cmd2
    7 root     top -b
    8 root     ps aux

$ /usr/bin/time docker stop test

test
real	0m 10.19s
user	0m 0.04s
sys	0m 0.03s

总结

介绍了 Dockerfile 中 ENTRYPOINT 指令的 shell 格式的使用。