How to start a stopped Docker container with a different command

Question

I would like to start a stopped Docker container with a different command  as the default command crashes - meaning I can t start the container and then use  docker exec     Basically I would like to start a shell so I can inspect the contents of the container   Luckily I created the container with the -it option

User · Answer

I took  Dmitriusan s answer and made it into an alias      alias docker-run-prev-container  prev container id    docker ps -aq   head -n1    amp  amp  docker commit   prev container id   prev container  prev container id   amp  amp  docker run -it --entrypoint bash  prev container  prev container id     Add this into your    bashrc aliases file  and you ll have a nifty new docker-run-prev-container alias which ll drop you into a shell in the previous container   Helpful for debugging failed docker builds

User · Answer

This is not exactly what you re asking for  but you can use docker export on a stopped container if all you want is to inspect the files   mkdir  TARGET DIR docker export  CONTAINER ID   tar -x -C  TARGET DIR

User · Answer

My Problem     I started a container with docker run  lt IMAGE NAME gt  And then added some files to this container Then I closed the container and tried to start it again withe same command as above  But when I checked the new files  they were missing when I run docker ps -a I could see two containers   That means every time I was running docker run  lt IMAGE NAME gt  command  new image was getting created   Solution  To work on the same container you created in the first place run follow these steps   docker ps to get container of your container docker container start  lt CONTAINER ID gt  to start existing container Then you can continue from where you left  e g  docker exec -it  lt CONTAINER ID gt   bin bash You can then decide to create a new image out of it

User · Answer

Edit this file  corresponding to your stopped container    vi  var lib docker containers 923   4f6 config json   Change the  Path  parameter to point at your new command  e g   bin bash  You may also set the  Args  parameter to pass arguments to the command   Restart the docker service  note this will stop all running containers    service docker restart   List your containers and make sure the command has changed   docker ps -a   Start the container and attach to it  you should now be in your shell   docker start -ai mad brattain   Worked on Fedora 22 using Docker 1 7 1   NOTE  If your shell is not interactive  e g  you did not create the original container with -it option   you can instead change the command to   bin sleep 600  or   bin tail -f  dev null  to give you enough time to do  docker exec -it CONTID  bin bash  as another way of getting a shell   NOTE2  Newer versions of docker have config v2 json  where you will need to change either Entrypoint or Cmd  thanks user60561

User · Answer

Add a check to the top of your Entrypoint script  Docker really needs to implement this as a new feature  but here s another workaround option for situations in which you have an Entrypoint that terminates after success or failure  which can make it difficult to debug   If you don t already have an Entrypoint script  create one that runs whatever command s  you need for your container  Then  at the top of this file  add these lines to entrypoint sh     Run once  hold otherwise if   -f  already ran     then     echo  Already ran the Entrypoint once  Holding indefinitely for debugging       cat fi touch already ran    Do your main things down here   To ensure that cat holds the connection  you may need to provide a TTY  I m running the container with my Entrypoint script like so   docker run -t --entrypoint entrypoint sh image name   This will cause the script to run once  creating a file that indicates it has already run  in the container s virtual filesystem   You can then restart the container to perform debugging   docker start container name   When you restart the container  the already ran file will be found  causing the Entrypoint script to stall with cat  which just waits forever for input that will never come  but keeps the container alive   You can then execute a debugging bash session   docker exec -i container name bash   While the container is running  you can also remove already ran and manually execute the entrypoint sh script to rerun it  if you need to debug that way

User · Answer

Find your stopped container id  docker ps -a   Commit the stopped container   This command saves modified container state into a new image user test image  docker commit  CONTAINER ID user test image   Start run with a different entry point   docker run -ti --entrypoint sh user test image   Entrypoint argument description  https   docs docker com engine reference run   entrypoint-default-command-to-execute-at-runtime  Note   Steps above just start a stopped container with the same filesystem state  That is great for a quick investigation  But environment variables  network configuration  attached volumes and other staff is not inherited  you should specify all these arguments explicitly   Steps to start a stopped container have been borrowed from here   last comment  https   github com docker docker issues 18078

[docker] How to start a stopped Docker container with a different command?

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