Is it possible to start a shell session in a running container without ssh

Question

I was naively expecting this command to run a bash shell in a running container     docker run  id of running container   bin bash   it looks like it s not possible  I get the error     2013 07 27 20 00 24 Internal server error  404 trying to fetch remote history for 27d757283842   So  if I want to run bash shell in a running container  ex  for diagnosis purposes   do I have to run an SSH server in it and loggin via ssh

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You can use  docker exec -it  lt container name gt  bash

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Since things are achanging  at the moment the recommended way of accessing a running container is using nsenter   You can find more information on this github repository  But in general you can use nsenter like this   PID   docker inspect --format    State Pid    lt container name or ID gt   nsenter --target  PID --mount --uts --ipc --net --pid   or you can use the wrapper docker-enter   docker-enter  lt container name or ID gt    A nice explanation on the topic can be found on J  r  me Petazzoni s blog entry  Why you don t need to run sshd in your docker containers

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Maybe you were mislead like myself into thinking in terms of VMs when developing containers  My advice  Try not to   Containers are just like any other process  Indeed you might want to  attach  to them for debugging purposes  think of  proc  env or strace -p   but that s a very special case   Normally you just  run  the process  so if you want to modify the configuration or read the logs  just create a new container and make sure you write the logs outside of it by sharing directories  writing to stdout  so docker logs  works  or something like that   For debugging purposes you might want to start a shell  then your code  then press CTRL-p   CTRL-q to leave the shell intact  This way you can reattach using   docker attach  lt container id gt    If you want to debug the container because it s doing something you haven t expect it to do  try to debug it  https   serverfault com questions 596994 how-can-i-debug-a-docker-container-initialization

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If the goal is to check on the application s logs  this post shows starting up tomcat and tailing the log as part of CMD  The tomcat log is available on the host using  docker logs containerid    http   blog trifork com 2013 08 15 using-docker-to-efficiently-create-multiple-tomcat-instances

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There are two ways   With attach    sudo docker attach 665b4a1e17b6  by ID   With exec     sudo docker exec - -t 665b4a1e17b6  by ID

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Here s my solution In the Dockerfile        RUN mkdir -p  opt ADD initd sh  opt  RUN chmod  x  opt initd sh ENTRYPOINT   quot  opt initd sh quot    In the initd sh file    bin bash      etc init d gearman-job-server start  etc init d supervisor start  very important     bin bash  After image is built you have two options using exec or attach   Use exec  preferred  and run  docker run --name  CONTAINER NAME -dt  IMAGE NAME  then docker exec -it  CONTAINER NAME  bin bash  and use CTRL   D to detach  Use attach and run  docker run --name  CONTAINER NAME -dit  IMAGE NAME  then docker attach  CONTAINER NAME  and use CTRL   P and CTRL   Q to detach Note  The difference between options is in parameter -i

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With docker 1 3  there is a new command docker exec  This allows you to enter a running docker   docker exec -it  id of running container  bash

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Just do  docker attach container name   As mentioned in the comments  to detach from the container without stopping it  type Ctrlpthen Ctrlq

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No  This is not possible  Use something like supervisord to get an ssh server if that s needed  Although  I definitely question the need

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It s useful assign name when running container  You don t need refer container id   docker run --name container name yourimage  docker exec -it container name bash

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EDIT  Now you can use docker exec -it  id of running container  bash  doc   Previously  the answer to this question was   If you really must and you are in a debug environment  you can do this  sudo lxc-attach -n  lt ID gt  Note that the id needs to be the full one  docker ps -notrunc    However  I strongly recommend against this   notice  -notrunc is deprecated  it will be replaced by --no-trunc soon

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Keep an eye on this pull request  https   github com docker docker pull 7409  Which implements the forthcoming docker exec  lt container id gt   lt command gt  utility  When this is available it should be possible to e g  start and stop the ssh service inside a running container   There is also nsinit to do this   nsinit provides a handy way to access a shell inside a running container s namespace   but it looks difficult to get running  https   gist github com ubergarm ed42ebbea293350c30a6

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First thing you cannot run   docker run  existing container  command   Because this command is expecting an image and not a container and it would anyway result in a new container being spawned  so not the one you wanted to look at   I agree with the fact that with docker we should push ourselves to think in a different way  so you should find ways so that you don t need to log onto the container   but I still find it useful and this is how I work around it   I run my commands through supervisor in DEAMON mode   Then I execute what I call docker loop sh The content is pretty much this      bin bash  usr bin supervisord  usr bin supervisorctl while   true       do     echo  Detach with Ctrl-p Ctrl-q  Dropping to shell      sleep 1      bin bash done   What it does is that it allows you to  attach  to the container and be presented with the supervisorctl interface to stop start restart and check logs  If that should not suffice  you can Ctrl D and you will drop into a shell that will allow you to have a peek around as if it was a normal system   PLEASE DO ALSO TAKE INTO ACCOUNT that this system is not as secure as having the container without a shell  so take all the necessary steps to secure your container

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first  get the container id of the desired container by   docker ps   you will get something like this   CONTAINER ID        IMAGE                  COMMAND             CREATED             STATUS                          PORTS                    NAMES 3ac548b6b315        frontend react-web      npm run start      48 seconds ago      Up 47 seconds                   0 0 0 0 3000- gt 3000 tcp   frontend react-web 1    now copy this container id and run the following command   docker exec -it container id sh  docker exec -it 3ac548b6b315 sh

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There is actually a way to have a shell in the container   Assume your  root run sh launches the process  process manager  supervisor   or whatever   Create  root runme sh with some gnu-screen tricks     Spawn a screen with two tabs screen -AdmS  main   root run sh screen -S  main  -X screen bash -l screen -r  main    Now  you have your daemons in tab 0  and an interactive shell in tab 1  docker attach at any time to see what s happening inside the container   Another advice is to create a  development bundle  image on top of the production image with all the necessary tools  including this screen trick

[docker] Is it possible to start a shell session in a running container (without ssh)

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