容器启动直接退出，想进入容器调试改怎么办
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
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 upcontainerENTRYPOINT
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 ENTRYPOINTENTRYPOINT&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 mixeddocker-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 cmdEntrypoint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。
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
暂无评论内容