dockerfile 中CMD 和 ENTRYPOINT 协作结果

心已赠人 2022-02-02 20:59 245阅读 0赞

### dockerfile 中CMD 和 ENTRYPOINT 协作结果 ###

*   *  简介
     *  规则
     *  结果
     *  注意
     *  引用

## 简介 ##

docker在非特权模式下，启动顺序由cmd和ENTRYPOINT 来控制，不是原有linux那一套启动流程，下面是  
CMD 和 ENTRYPOINT 相互协作最终的命令执行结果，没时间翻译，直接官方粘过来的

## 规则 ##

Both `CMD` and `ENTRYPOINT` instructions define what command gets executed when running a container. There are few rules that describe their co-operation.

*  Dockerfile should specify at least one of `CMD` or `ENTRYPOINT` commands.
 *  `ENTRYPOINT` should be defined when using the container as an executable.
 *  `CMD` should be used as a way of defining default arguments for an `ENTRYPOINT` command or for executing an ad-hoc command in a container.
 *  `CMD` will be overridden when running the container with alternative arguments.

The table below shows what command is executed for different `ENTRYPOINT` / `CMD` combinations:

## 结果 ##

The table below shows what command is executed for different ENTRYPOINT / CMD combinations:

<table> 
 <thead> 
  <tr> 
   <th></th> 
   <th>No ENTRYPOINT</th> 
   <th>ENTRYPOINT exec_entry p1_entry</th> 
   <th>ENTRYPOINT [“exec_entry”, “p1_entry”]</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td><code>No CMD</code></td> 
   <td>error, not allowed</td> 
   <td>/bin/sh -c exec_entry p1_entry</td> 
   <td>exec_entry p1_entry</td> 
  </tr> 
  <tr> 
   <td><code>CMD [“exec_cmd”, “p1_cmd”]</code></td> 
   <td>exec_cmd p1_cmd</td> 
   <td>/bin/sh -c exec_entry p1_entry</td> 
   <td>exec_entry p1_entry exec_cmd p1_cmd</td> 
  </tr> 
  <tr> 
   <td><code>CMD [“p1_cmd”, “p2_cmd”]</code></td> 
   <td>p1_cmd p2_cmd</td> 
   <td>/bin/sh -c exec_entry p1_entry</td> 
   <td>exec_entry p1_entry p1_cmd p2_cmd</td> 
  </tr> 
  <tr> 
   <td><code>CMD exec_cmd p1_cmd</code></td> 
   <td>/bin/sh -c exec_cmd p1_cmd</td> 
   <td>/bin/sh -c exec_entry p1_entry</td> 
   <td>exec_entry p1_entry /bin/sh -c exec_cmd p1_cmd</td> 
  </tr> 
 </tbody> 
</table>

## 注意 ##

Note: If `CMD` is defined from the base image, setting `ENTRYPOINT` will reset `CMD` to an empty value. In this scenario, `CMD` must be defined in the current image to have a value.

## 引用 ##

> https://docs.docker.com/engine/reference/builder/\#entrypoint  
> k8s 规则  
> https://kubernetes.io/zh/docs/tasks/inject-data-application/define-command-argument-container/