docker mounting volumes on host

Question

I have successfully been able to share folders between a docker container with volumes using  docker run -v  host path  container path       But my question is what the difference between this and using the VOLUME command in the Dockerfile  VOLUME  path   I am using an image that has a VOLUME command  and I d like to know how to share it with my host  I have done it using the -v command above  but I didn t know if I needed both the -v and VOLUME

User · Accepted Answer

The VOLUME command will mount a directory inside your container and store any files created or edited inside that directory on your hosts disk outside the container file structure  bypassing the union file system   The idea is that your volumes can be shared between your docker containers and they will stay around as long as there s a container  running or stopped  that references them   You can have other containers mount existing volumes  effectively sharing them between containers  by using the --volumes-from command when you run a container   The fundamental difference between VOLUME and -v is this  -v will mount existing files from your operating system inside your docker container and VOLUME will create a new  empty volume on your host and mount it inside your container   Example    You have a Dockerfile that defines a VOLUME  var lib mysql  You build the docker image and tag it some-volume You run the container   And then    You have another docker image that you want to use this volume You run the docker container with the following  docker run --volumes-from some-volume docker-image-name tag Now you have a docker container running that will have the volume from some-volume mounted in  var lib mysql   Note  Using --volumes-from will mount the volume over whatever exists in the location of the volume  I e   if you had stuff in  var lib mysql  it will be replaced with the contents of the volume

User · Answer

Let me add my own answer  because I believe the others are missing the point of Docker   Using VOLUME in the Dockerfile is the Right Way     because you let Docker know that a certain directory contains permanent data  Docker will create a volume for that data and never delete it  even if you remove all the containers that use it   It also bypasses the union file system  so that the volume is in fact an actual directory that gets mounted  read-write or readonly  in the right place in all the containers that share it   Now  in order to access that data from the host  you only need to inspect your container     docker inspect myapp                           Volumes               var www     var lib docker vfs dir b3ef4bc28fb39034dd7a3aab00e086e6                var cache nginx     var lib docker vfs dir 62499e6b31cb3f7f59bf00d8a16b48d2                var log nginx     var lib docker vfs dir 71896ce364ef919592f4e99c6e22ce87                 VolumesRW               var www   false            var cache nginx   true            var log nginx   true            What I usually do is make symlinks in some standard place such as  srv  so that I can easily access the volumes and manage the data they contain  only for the volumes you care about    ln -s  var lib docker vfs dir b3ef4bc28fb39034dd7a3aab00e086e6     srv myapp-www ln -s  var lib docker vfs dir 71896ce364ef919592f4e99c6e22ce87     srv myapp-log

User · Answer

If you came here because you were looking for a simple way to browse any VOLUME   Find out the name of the volume with docker volume list Shut down all running containers to which this volume is attached to Run docker run -it --rm --mount source  NAME OF VOLUME  target  volume busybox A shell will open  cd  volume to enter the volume

User · Answer

This is from the Docker documentation itself  might be of help  simple and plain     The host directory is  by its nature  host-dependent  For this reason  you can   t mount a host directory from Dockerfile  the VOLUME instruction does not support passing a host-dir  because built images should be portable  A host directory wouldn   t be available on all potential hosts

User · Answer

Basically VOLUME and -v option are almost equal  These mean  mount specific directory on your container   For example  VOLUME  data and -v  data is exactly same meaning  If you run the image that have VOLUME  data or with -v  data option   data directory is mounted your container  This directory doesn t belong to your container    Imagine that You add some files to  data on the container  then commit the container into new image  There isn t any files on data directory because mounted  data directory is belong to original container     docker run -it -v  data --name volume ubuntu 14 04 bash root 2b5e0f2d37cd    cd  data root 2b5e0f2d37cd  data  touch 1 2 3 4 5 6 7 8 9 root 2b5e0f2d37cd  data  cd  tmp root 2b5e0f2d37cd  tmp  touch 1 2 3 4 5 6 7 8 9 root 2b5e0f2d37cd  tmp  exit exit    docker commit volume nacyot volume   835cfe3d8d159622507ba3256bb1c0b0d6e7c1419ae32751ad0f925c40378945 nacyot   docker run -it nacyot volume root dbe335c7e64d    cd  data root dbe335c7e64d  data  ls root dbe335c7e64d  data  cd  tmp root dbe335c7e64d  tmp  ls 1  2  3  4  5  6  7  8  9 root dbe335c7e64d  tmp   root dbe335c7e64d  tmp     This mounted directory like  data is used to store data that is not belong to your application  And you can predefine the data directory that is not belong to the container by using VOLUME   A difference between Volume and -v option is that you can use -v option dynamically on starting container  It mean you can mount some directory dynamically  And another difference is that you can mount your host directory on your container by using -v

User · Answer

VOLUME is used in Dockerfile to expose the volume to be used by other containers  Example  create Dockerfile as   FROM ubuntu 14 04    RUN mkdir  myvol   RUN echo  hello world   gt   myvol greeting   VOLUME  myvol   build the image     docker build -t testing volume      Run the container  say container1     docker run -it  lt image-id of above image gt  bash  Now run another container with volumes-from option as  say-container2       docker run -it --volumes-from  lt id-of-above-container gt  ubuntu 14 04 bash  You will get all data from container1  myvol directory into container2 at same location   -v option is given at run time of container which is used to mount container s directory on host  It is simple to use  just provide -v option with argument as  lt host-path gt   lt container-path gt     The whole command may be as   docker run -v  lt host-path gt   lt container-path gt   lt image-id gt

[docker] docker mounting volumes on host

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