docker容器直接退出，如何进入容器调试

使用过docker的朋友大概率会遇到docker启动容器失败或执行完直接退出的情况，如果我想进入容器手动执行命令调试，该怎么办呐？

docker容器启动失败正常都是由于启动主进程退出导致的，主进程启动命令往往都是由镜像Dockerfile文件最后的ENTRYPOINT或CMD定义的，此时可覆盖主进程启动命令，更换一个挂起的命令即可。我常用挂起命令：/bin/bash

所以，我们要解决的核心问题就是：如何使用挂起命令覆盖ENTRYPOINT或CMD定义的容器主进程命令？

先上结论（适用所有镜像）

1. docker run -it --entrypoint /bin/bash 镜像，执行后直接进入容器。

2. 若docker-compose启动容器，则需要修改docker-compose.yml文件，在对应服务下增加如下高亮显示信息；然后docker-compose重新up

version: '3'
services:
  cmd:
    image: 镜像
    container_name: 容器名
    entrypoint:
    - tail
    - -f
    - /dev/null

执行命令进入容器 docker exec -it 容器名 /bin/bash

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以下为详细分析过程：

查看镜像的dockerfile文件（docker history --no-trunc image），检查最后容器启动主进程的命令是什么样的，ENTRYPOINT？CMD？还是它们的组合？覆盖方式稍有不同。为方便演示，我构造了一个简单Dockerfile文件做案例。

Docker RUN 覆盖容器主进程命令

docker run 使用-it交互参数，覆盖命令/bin/bash

CMD

FROM centos:latest
MAINTAINER quanling
CMD ["echo","hello World"]

如果使用上面的文件创建镜像test:cmd，使用history命令查看容器主进程命令，下方橙色标记部分

[root@localhost docker]# docker history --no-trunc test:cmd
IMAGE                                                                     CREATED          CREATED BY                                                                                                                                                                                                SIZE      COMMENT
sha256:694d5f2d8809ef2847a9b6fd46efed49ab59aa6466784a1e783beb25c2f6c16e   31 seconds ago   /bin/sh -c #(nop)  CMD ["echo" "hello World"]                                                                                                                                                             0B        
sha256:6dcafb4f0c8d93e8793f84bb837ef26ed6293c156dafafbbc520e55ed601a09e   16 minutes ago   /bin/sh -c #(nop)  MAINTAINER quanling                                                                                                                                                                    0B        
sha256:5d0da3dc976460b72c77d94c8a1ad043720b0416bfc16c52c45d4847e53fadb6   3 months ago     /bin/sh -c #(nop)  CMD ["/bin/bash"]                                                                                                                                                                      0B        
<missing>                                                                 3 months ago     /bin/sh -c #(nop)  LABEL org.label-schema.schema-version=1.0 org.label-schema.name=CentOS Base Image org.label-schema.vendor=CentOS org.label-schema.license=GPLv2 org.label-schema.build-date=20210915   0B        
<missing>                                                                 3 months ago     /bin/sh -c #(nop) ADD file:805cb5e15fb6e0bb0326ca33fd2942e068863ce2a8491bb71522c652f31fb466 in /     

运行容器后成功打印出Hello World后容器直接退出。容器状态为Exited(0)。此时容器启动的主进程为橙色标记部分

[root@localhost docker]# docker run --name cmd test:cmd
hello World
[root@localhost docker]# docker ps -a
CONTAINER ID   IMAGE      COMMAND                CREATED         STATUS                     PORTS     NAMES
6bc94359c4fd   test:cmd   "echo 'hello World'"   4 seconds ago   Exited (0) 3 seconds ago             cmd

若想让容器一直up状态，方便进入容器进一步操作，需要使用挂起命令覆盖CMD ["echo","hello World"]，

方法1：在命令中增加绿色高亮部分代码（额外增加-it选项可直接进入容器）。进入容器成功

[root@localhost docker]# docker run -it --name upcontainer test:cmd /bin/bash
[root@9351844319e3 /]#

更换tty窗口，查看容器状态Up。此时容器启动的主进程入橙色标记部分，说明覆盖CMD成功

[root@localhost ~]# docker ps -a
CONTAINER ID   IMAGE      COMMAND                CREATED          STATUS                     PORTS     NAMES
9351844319e3   test:cmd   "/bin/bash"           11 seconds ago   Up 10 seconds                         upcontainer

方法2：在命令中增加绿色高亮部分代码（额外增加-it选项可直接进入容器）。进入容器成功

[root@localhost docker]# docker run --name upcontainer -it --entrypoint /bin/bash test:cmd 
[root@50763cf9a838 /]# 

更换tty窗口，查看容器状态Up。此时容器启动的主进程入橙色标记部分，说明覆盖CMD成功

[root@localhost ~]# docker ps
CONTAINER ID   IMAGE      COMMAND       CREATED              STATUS              PORTS     NAMES
50763cf9a838   test:cmd   "/bin/bash"   About a minute ago   Up About a minute             upcontainer

 ENTRYPOINT

FROM centos:latest
MAINTAINER quanling
ENTRYPOINT ["echo","Hello World"]

如果使用上面的文件创建镜像test:ENTRYPOINT

运行容器后成功打印出Hello World后容器直接退出。容器状态为Exited(0)。此时容器启动的主进程入橙色标记部分

[root@localhost docker]# docker run --name ENTRYPOINT test:ENTRYPOINT
Hello World
[root@localhost docker]# docker ps -a
CONTAINER ID   IMAGE             COMMAND                CREATED         STATUS                     PORTS     NAMES
e6cf335c5c09   test:ENTRYPOINT   "echo 'Hello World'"   8 seconds ago   Exited (0) 6 seconds ago             ENTRYPOINT

若想让容器一直up状态，方便exec进入容器进一步操作，需要使用挂起命令覆盖ENTRYPOINT["echo","hello World"]，模仿上面的操作，结果如下，容器Exited状态（--no-trunc显示全输出信息）

[root@localhost docker]# docker run --name upcontainer test:ENTRYPOINT /bin/bash
Hello World /bin/bash[root@localhost docker]# docker ps -a --no-trunc
CONTAINER ID                                                       IMAGE             COMMAND                                  CREATED         STATUS                     PORTS     NAMES
0476c3014fa4c28615b72c231971c6b5186a310f9b2f5cae466643d65b236c34   test:ENTRYPOINT   "echo 'Hello World' /bin/bash"   2 minutes ago   Exited (0) 2 minutes ago             upcontainer
e6cf335c5c09df35845f40abfd81594e17b3457891128ee2108414d7573e62a3   test:ENTRYPOINT   "echo 'Hello World'"                     7 minutes ago   Exited (0) 7 minutes ago             ENTRYPOINT

我们想执行的挂起命令并未覆盖ENTRYPOINT命令，反而作为echo命令的参数部分一起输出了。因为覆盖ENTRYPOINT命令需要使用--entrypoint设置（额外增加-it选项可直接进入容器），进入容器成功。

[root@localhost docker]# docker run -it --entrypoint /bin/bash --name upcontainer test:ENTRYPOINT
[root@4fe14a5e7bd1 /]#

更换tty窗口，查看容器状态Up。此时容器启动的主进程入橙色标记部分，说明覆盖ENTRYPOINT成功

[root@localhost ~]# docker ps -a
CONTAINER ID   IMAGE             COMMAND                CREATED          STATUS                      PORTS     NAMES
4fe14a5e7bd1   test:ENTRYPOINT   "/bin/bash"            11 seconds ago   Up 10 seconds                         upcontainer
e6cf335c5c09   test:ENTRYPOINT "echo 'Hello World'" 14 minutes ago Exited (0) 14 minutes ago ENTRYPOINT

ENTRYPOINT&CMD

FROM centos:latest
MAINTAINER quanling
ENTRYPOINT ["echo"]
CMD ["hello World"]

如果使用上面的文件创建镜像test:mixed。使用history命令查看容器主进程命令，下方橙色标记部分

[root@localhost docker]# docker history --no-trunc test:mixed
IMAGE                                                                     CREATED          CREATED BY                                                                                                                                                                                                SIZE      COMMENT
sha256:2c1f8303382cb221fac04a76234d0b1afe3a513205267afe2d01f39006877be8   24 seconds ago   /bin/sh -c #(nop)  CMD ["hello World"]                                                                                                                                                                    0B        
sha256:13608f257d7b6d1ae771af1aec482b7b87650703648a4ac5c03e8715f78c0079   25 seconds ago   /bin/sh -c #(nop)  ENTRYPOINT ["echo"]                                                                                                                                                                    0B        
sha256:6dcafb4f0c8d93e8793f84bb837ef26ed6293c156dafafbbc520e55ed601a09e   2 hours ago      /bin/sh -c #(nop)  MAINTAINER quanling                                                                                                                                                                    0B        
sha256:5d0da3dc976460b72c77d94c8a1ad043720b0416bfc16c52c45d4847e53fadb6   3 months ago     /bin/sh -c #(nop)  CMD ["/bin/bash"]                                                                                                                                                                      0B        
<missing>                                                                 3 months ago     /bin/sh -c #(nop)  LABEL org.label-schema.schema-version=1.0 org.label-schema.name=CentOS Base Image org.label-schema.vendor=CentOS org.label-schema.license=GPLv2 org.label-schema.build-date=20210915   0B        
<missing>                                                                 3 months ago     /bin/sh -c #(nop) ADD file:805cb5e15fb6e0bb0326ca33fd2942e068863ce2a8491bb71522c652f31fb466 in /                                                                                                          231MB

运行容器后成功打印出Hello World后容器直接退出。容器状态为Exited(0)。此时容器启动的主进程为橙色标记部分

[root@localhost docker]# docker run --name mixed test:mixed
hello World
[root@localhost docker]# docker ps -a
CONTAINER ID   IMAGE      COMMAND                CREATED         STATUS                     PORTS     NAMES
22362d314132   test:mixed   "echo 'hello World'"   4 seconds ago   Exited (0) 3 seconds ago             mixed

若想让容器一直up状态，方便进入容器进一步操作，需要覆盖Etrypoint和CMD中命令，在命令中增加绿色高亮部分代码（额外增加-it选项可直接进入容器）。查看执行结果 

[root@localhost docker]# docker run -it --name upcontainer test:mixed /bin/bash
/bin/bash
[root@localhost docker]# docker ps -a
CONTAINER ID   IMAGE        COMMAND                CREATED         STATUS                     PORTS     NAMES
df18afb54646   test:mixed   "echo /bin/bash"       6 seconds ago   Exited (0) 5 seconds ago             upcontainer
22362d314132   test:mixed   "echo 'hello World'"   3 minutes ago   Exited (0) 3 minutes ago             mixed

执行发现容器为Exited状态，打印出“/bin/bash”后容器退出。说明该操作仅仅覆盖了CMD ["hello World"]部分，保留了ENTRYPOINT ["echo"]部分。正确的操作应该使用--entrypoint设置（额外增加-it选项可直接进入容器），进入容器成功。

[root@localhost docker]# docker run -it --entrypoint /bin/bash --name upcontainer test:mixed 
[root@deb56cf88e89 /]#

更换tty窗口，查看容器状态Up。此时容器启动的主进程入橙色标记部分，说明覆盖ENTRYPOINT成功

[root@localhost ~]# docker ps -a
CONTAINER ID   IMAGE        COMMAND                CREATED              STATUS                     PORTS     NAMES
deb56cf88e89   test:mixed   "/bin/bash"            About a minute ago   Up About a minute                   upcontainer
22362d314132   test:mixed   "echo 'hello World'"   8 minutes ago        Exited (0) 8 minutes ago             mixed

docker-compose中的覆盖主进程命令

有些容器是使用docker-compose来启动容器的，按照Dockerfile文件的不同，docker-compose中的修改不同，覆盖命令 tail -f /dev/null

利用上面三个镜像，编写docker-compose.yml文件

version: '3'
services:
  cmd:
    image: test:cmd
    container_name: cmd
  ENTRYPOINT:
    image: test:ENTRYPOINT
    container_name: ENTRYPOINT
  mixed:
    image: test:mixed
    container_name: mixed

启动三个镜像的服务容器，都执行后退出Exited状态。容器主进程见下方橙色高亮部分

[root@localhost docker]# docker-compose up -d
Starting cmd        ... done
Creating ENTRYPOINT ... done
Creating mixed      ... done
[root@localhost docker]# docker ps -a
CONTAINER ID   IMAGE             COMMAND                CREATED          STATUS                      PORTS     NAMES
7519cbfb6ef8   test:mixed        "echo 'hello World'"   40 seconds ago   Exited (0) 36 seconds ago             mixed
d1c2709a0173   test:ENTRYPOINT   "echo 'Hello World'"   40 seconds ago   Exited (0) 36 seconds ago             ENTRYPOINT
e2206ea2cfc1   test:cmd          "echo 'hello World'"   2 minutes ago    Exited (0) 37 seconds ago             cmd

Entrypoint命令

 在docker-compose.yaml 文件中每个服务下添加以下绿色高亮区域命令，以覆盖原来docker中的命令 

version: '3'
services:
  cmd:
    image: test:cmd
    container_name: cmd
    entrypoint:
    - tail
    - -f
    - /dev/null
  ENTRYPOINT:
    image: test:ENTRYPOINT
    container_name: ENTRYPOINT
    entrypoint:
    - tail
    - -f
    - /dev/null
  mixed:
    image: test:mixed
    container_name: mixed
    entrypoint:
    - tail
    - -f
    - /dev/null

重新启动容器，容器全部为up状态，主程序命令被替换为"tail -f /dev/null"

[root@localhost docker]# docker-compose up -d
Starting mixed        ... done
Starting cmd          ... done
Recreating ENTRYPOINT ... done
[root@localhost docker]# docker ps -a
CONTAINER ID   IMAGE             COMMAND               CREATED          STATUS          PORTS     NAMES
2d4682226bb0   test:cmd          "tail -f /dev/null"   4 seconds ago    Up 2 seconds              cmd
c3870ab0d462   test:mixed        "tail -f /dev/null"   31 seconds ago   Up 28 seconds             mixed
7320deecd45a   test:ENTRYPOINT   "tail -f /dev/null"   59 seconds ago   Up 55 seconds             ENTRYPOINT

Command命令

在docker-compose.yaml 文件中每个服务下添加以下绿色高亮区域命令

version: '3'
services:
  cmd:
    image: test:cmd
    container_name: cmd
    command: tail -f /dev/null
  ENTRYPOINT:
    image: test:ENTRYPOINT
    container_name: ENTRYPOINT
    command: tail -f /dev/null
  mixed:
    image: test:mixed
    container_name: mixed
    command: tail -f /dev/null

重新启动容器，查看容器状态，及主程序命令

[root@localhost docker]# docker-compose up -d
cmd is up-to-date  ... done
Recreating ENTRYPOINT ... done
Recreating mixed      ... done
[root@localhost docker]# docker ps -a --no-trunc
CONTAINER ID                                                       IMAGE             COMMAND                                  CREATED              STATUS                          PORTS     NAMES
bf67da0ba9815a013a2005d61daa223e31586bf1cde279933ba71d0148c721ff   test:mixed        "echo tail -f /dev/null"                 About a minute ago   Exited (0) About a minute ago             mixed
f019610b1aedb54904704227ae661f421786b72ecc9e3b35154442c4717afcb0   test:ENTRYPOINT   "echo 'Hello World' tail -f /dev/null"   About a minute ago   Exited (0) About a minute ago             ENTRYPOINT
224bc6db4563531c68947a38acbf3418c43149b2ef6a92565f940a98ab1a9b1e   test:cmd          "tail -f /dev/null"                      10 minutes ago       Up 10 minutes                             cmd

分析结论

使用commad命令，结果仅test:cmd中命令被替换；test:Entrypoint镜像未被覆盖，且commad命令作为参数传入；test:mixed镜像仅CMD部分命令被替换，ENTRYPOINT部分未被替换。与docker run运行结果一致。

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补充

容器up状态时，执行exec命令进入容器

# docker exec -it  容器名 /bin/bash

容器内查看相关配置是否符合预期，手动执行镜像原entrypoint/cmd命令跟着日志进行调试

镜像往往很精简，不包含yum、vi 等命令，导致需要修改配置进行调试受阻，除安装所需命令这个麻烦的方法外，还可以在容器外使用docker cp命令

$ docker cp  容器名:文件完整路径  本地路径    #容器内文件copy到本地

$ docker cp 本地文件 容器名:文件完整路径      #本地文件copy到容器内

 $ docker run -it --rm --entrypoint="" 容器名 /bin/bash