I lose my data when the container exits

Question

Despite Docker s Interactive tutorial and faq I lose my data when the container exits   I have installed Docker as described here  http   docs docker io en latest installation ubuntulinux without any problem on ubuntu 13 04   But it loses all data when exits   iman test    sudo docker version Client version  0 6 4  Go version  client   go1 1 2  Git commit  client   2f74b1c  Server version  0 6 4  Git commit  server   2f74b1c  Go version  server   go1 1 2  Last stable version  0 6 4    iman test    sudo docker run ubuntu ping 2013 10 25 08 05 47 Unable to locate ping  iman test    sudo docker run ubuntu apt-get install ping Reading package lists     Building dependency tree     The following NEW packages will be installed     iputils-ping  0 upgraded  1 newly installed  0 to remove and 0 not upgraded   Need to get 56 1 kB of archives   After this operation  143 kB of additional disk space will be used   Get 1 http   archive ubuntu com ubuntu  precise main iputils-ping amd64 3 20101006-1ubuntu1  56 1 kB   debconf  delaying package configuration  since apt-utils is not installed  Fetched 56 1 kB in 0s  195 kB s   Selecting previously unselected package iputils-ping    Reading database     7545 files and directories currently installed    Unpacking iputils-ping  from     iputils-ping 3 3a20101006-1ubuntu1 amd64 deb       Setting up iputils-ping  3 20101006-1ubuntu1       iman test    sudo docker run ubuntu ping 2013 10 25 08 06 11 Unable to locate ping  iman test    sudo docker run ubuntu touch  home test iman test    sudo docker run ubuntu ls  home test ls  cannot access  home test  No such file or directory    I also tested it with interactive sessions with the same result  Did I forget something   EDIT  IMPORTANT FOR NEW DOCKER USERS  As  mohammed-noureldin and others said  actually this is NOT a container exiting  Every time it just creates a new container

User · Answer

There are really great answers above to the asked question. There might be no need for another answer but still I want to give my personal opinion on the topic in the simplest words possible.

Here are some points about containers & images that will help us for a conclusion:

A docker image can be:
1. created-from-a-given-container
2. deleted
3. used-to-create-any-number-of-containers
A docker container can be:
1. created-from-an-image
2. started
3. stopped
4. restarted
5. deleted
6. used-to-create-any-number-of-images
A docker run command does this:
1. Downloads an image or uses a cached image
2. Creates a new container out of it
3. Starts the container
When a Dockerfile is used to create an image:
1. It is already well known that the image will eventually be used to run a docker container.
2. After issuing docker build command, docker behind-the-scenes creates a running container with a base-file-system and follows steps inside the Dockerfile to configure that container as per the developers need.
3. After the container is configured with specs of the Dockerfile, it will be committed as an image.
4. The image gets ready to rock & roll!

Conclusion:

As we can see, a docker container is independent of a docker image.

A container can be restarted provided the unique ID of that container [use docker ps --all to get the id].

Any operation like making a new directory, creating files, installing tools, etc. can be done inside the container when it is running. Once the container is stopped, it persists all the changes. Container stopping and restarting is like rebooting a computer system.

An already created container is always available for a restart but when we issue docker run command, a new container is created out of an image and hence it is like a new computer system. The changes made inside the old container - as we can understand now - are not available in this new container.

A final note:

I guess it's now obvious why the data seems to be lost yet it is always there.. but in a different [old] container. So, take a good note of the difference in docker start & docker run command & never get confused in them.

User · Answer

a brilliant answer here  How to continue a docker which is exited  from user kgs  docker start   docker ps -a -q --filter  status exited    or in this case just docker start   docker ps -ql   cos you don t want to start all of them   docker exec -it  lt container-id gt   bin bash   That second line is crucial   So exec is used in place of run  and not on an image but on a containerid  And you do it after the container has been started

User · Answer

None of the answers address the point of this design choice  I think docker works this way to prevent these 2 errors    Repeated restart Partial error

User · Answer

There are following ways to persist container data    Docker volumes Docker commit  a  create container from ubuntu image and run a bash terminal        docker run -i -t ubuntu 14 04  bin bash   b  Inside the terminal install curl       apt-get update      apt-get install curl   c  Exit the container terminal       exit   d  Take a note of your container id by executing following command         docker ps -a   e  save container as new image       docker commit  lt container id gt  new image name tag name optional    f  verify that you can see your new image with curl installed        docker images                  docker run -it new image name tag name bash         which curl          usr bin curl

User · Answer

In addition to Unferth s answer  it is recommended to create a Dockerfile   In an empty directory  create a file called  Dockerfile  with the following contents   FROM ubuntu RUN apt-get install ping ENTRYPOINT   ping     Create an image using the Dockerfile  Let s use a tag so we don t need to remember the hexadecimal image number     docker build -t iman ping     And then run the image in a container     docker run iman ping stackoverflow com

User · Answer

You might want to look at docker volumes if you you want to persist the data in your container  Visit https   docs docker com engine tutorials dockervolumes   The docker documentation is a very good place to start

User · Answer

My suggestion is to manage docker  with docker compose  Is an easy to way to manage all the docker s containers for your project  you can map the versions and link different containers to work together   The docs are very simple to understand  better than docker s docs   Docker-Compose Docs  Best

User · Answer

You need to commit the changes you make to the container and then run it  Try this   sudo docker pull ubuntu  sudo docker run ubuntu apt-get install -y ping   Then get the container id using this command   sudo docker ps -l   Commit changes to the container   sudo docker commit  lt container id gt  iman ping    Then run the container   sudo docker run iman ping ping www google com   This should work

User · Answer

the similar problem  and no way Dockerfile alone could fix it  brought me to this page   stage 0  for all  hoping Dockerfile could fix it  until --dns and --dns-search will appear in Dockerfile support - there is no way to integrate intranet based resources into   stage 1  after building image using Dockerfile  by the way it s a serious glitch Dockerfile must be in the current folder   having an image to deploy what s intranet based  by running docker run script  example       docker run -d       --dns   DNSLOCAL        --dns   DNSGLOBAL        --dns-search intranet       -t pack bsp       --name packbsp-cont       bash -c         wget -r --no-parent http   intranet intranet-content tar gz       tar -xvf intranet-content tar gz       sudo -u   USERNAME  bash --norc    stage 2  applying docker run script in daemon mode providing local dns records to have ability to download and deploy local stuff    important point  run script should be ending with something like  usr bin sudo -u   USERNAME  bash --norc to keep container running even after the installation scripts finishes    no  it s not possible to run container in interactive mode for the full automation matter as it will remain inside internal shall command prompt until CTRL-p CTRL-q being pressed    no  if interacting bash will not be executed at the end of the installation script  the container will terminate immediately after finishes script execution  loosing all installation results   stage 3  container is still running in background but it s unclear whether container has ended installation procedure or not yet  using following block to determine execution procedure finishes        while   docker container top   CONTNAME    grep  00   space     12  bash  --norc  -     do     echo         sleep 5     done  the script will proceed further only after completed installation  and this is the right moment to call  commit  providing current container id as well as destination image name  it may be the same as on the build run procedure but appended with the local installation purposes tag  example  docker commit containerID pack bsp toolchained  see this link on how to get proper containerID  stage 4  container has been updated with the local installs as well as it has been committed into newly assigned image  the one having purposes tag added   it s safe now to stop container running  example  docker stop packbsp-cont  stage5  any moment the container with local installs require to run  start it with the image previously saved  example  docker run -d -t pack bsp toolchained

User · Answer

When you use docker run to start a container  it actually creates a new container based on the image you have specified   Besides the other useful answers here  note that you can restart an existing container after it exited and your changes are still there   docker start f357e2faab77   restart it in the background docker attach f357e2faab77   reattach the terminal  amp  stdin

User · Answer

I have got a much simpler answer to your question  run the following two commands  sudo docker run -t -d ubuntu --name mycontainername  bin bash sudo docker ps -a   the above ps -a command returns a list of all containers  Take the name of the container which references the image name -  ubuntu    docker auto generates names for the containers for example -  lightlyxuyzx   that s if you don t use the --name option   The -t and -d options are important  the created container is detached and can be reattached as given below with the -t option   With --name option  you can name your container in my case  mycontainername    sudo docker exec -ti mycontainername bash   and this above command helps you login to the container with bash shell  From this point on any changes you make in the container is automatically saved by docker   For example - apt-get install curl inside the container You can exit the container without any issues  docker auto saves the changes   On the next usage  All you have to do is  run these two commands every time you want to work with this container   This Below command will start the stopped container   sudo docker start mycontainername  sudo docker exec -ti mycontainername bash   Another example with ports and a shared space given below   docker run -t -d --name mycontainername -p 5000 5000 -v   PROJECTS SPACE  PROJECTSPACE 7efe2989e877  bin bash   In my case  7efe2989e877 - is the imageid of a previous container running  which I obtained using      docker ps -a

[docker] I lose my data when the container exits

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