I see there are three docker commands that seem to do very similar things:
docker build
docker create
docker run
What are the differences between these commands?
docker build builds a new image from the source code.
docker create creates a writeable container from the image and prepares it for running.
docker run creates the container (same as docker create) and runs it.
docker build . converts your Dockerfile into an image.
docker create your-image creates a container from your image from step 1.
docker start container_id starts the container from step 2.
docker run image is a shortcut for 2. and 3. (docker create image and
docker start container_id).
Here is the difference between image and container:
Image
An image is a specified snapshot of your filesystem and includes the starting command of your container. An image occupies just disk-space, it does not occupy memory/cpu. To create an image you usually create instructions how to build that image in aDockerfile. FROM and RUN commands in the docker file create the file-snapshot. One may build an image from a docker file with docker build <dockerfile>
Container
You can create new containers with an image. Each container has a file-snapshot which is based on the file-snapshot created by the image. If you start a container it will run the command you specified in your docker file CMD and will use part of your memory and cpu. You can start or stop a container. If you create a container, its not started by default. This means you can't communicate to the container via ports etc. You have to start it first. One may create an container from an image by docker create <image>. When a container has been created it shows the id in the terminal. One may start it with docker start <container_id>.
Related
OK so my requirement is to modify the docker image. Following are my steps:
Pull the docker image
Run the container.
Step into the container and modified the file.
Create an image from container
Stop the container
Rerun the container with new image.
I was expecting the file i had modified should be updated, but its not. Is there anything i am missing ?
You need to delete you image docker with docker rmi <imagename> for list all images run docker images
I have created a container using the following command: docker container run -i ubuntu. However, when I try to run a command within the container, such as cd, I get the following error: bash: line 1: cd: $'bin\r': No such file or directory. What could be the issue?
When you docker run an image, or use an image in a Dockerfile FROM line, or name an image: in a Docker Compose setup, Docker first checks to see if you have that image locally. If you have that image, Docker just uses it without checking Docker Hub or the other upstream registry.
Meanwhile, you can docker build or docker tag an image with any name you want...even a name that matches an official Docker Hub image.
You mention in a comment that you at some point did run docker build -t ubuntu .... That replaces the ubuntu image with what you built, so when you later docker run ubuntu, it's running your modified image and not the official Docker Hub Ubuntu image.
This is straightforward to fix. If you
docker rmi ubuntu
it will delete your local (modified) copy, and the next time you use it, Docker will automatically pull it from Docker Hub. It should also work to
# Explicitly get the Docker Hub copy of the image
docker pull ubuntu
# Build a custom image, pulling whatever's in the FROM line
docker build --pull -t my/image .
(You can also hit this in a Docker Compose setup if you specify both image: and build:; this instructs Compose on an explicit name to use for the built image. You do not need to repeat the FROM line in image:, and it causes trouble if you do. The resolution is the same as described above. I might leave image: out entirely unless you're planning to push the image to a registry.)
I tried to build a docker image. Then on docker images command, the list displays:
REPOSITORY TAG IMAGE ID CREATED SIZE
<none> <none> eaaf8e203bd4 1 min ago 253.2 MB
Is there a way in my Dockerfile to specify a name for this build? Or at docker build . command line?
Another question: I want to upload via SFTP the docker container on my production server and run it. Where are the containers stored?
You should use the -t option of docker build
docker build -t name:tag
The tag is optional.
I want to upload via SFTP the docker container on my production server and run it.
You should "upload" the image, and by that I mean push it to a docker registry running on your server.
You could also commit a running container into an intermediate image (which would freeze the running state of the container, but would not preserve the volume data, if one was declared in that container)
Then copy that archive, and docker import it.
See "How to move docker containers between different hosts".
Once imported, see "Where are docker images stored on the host machine?".
(/var/lib/docker/containers for containers)
I am running an instance of docker, and I would like to save my work - the docs just aren't 100% clear on how to do this, so I'm asking here. I opened the docker instance using:
docker run -it [public dockerhub name]
Now I would like to save all my work locally so that I can come back to it. I don't particularly want to check it into dockerhub, unless that's advisable.
Here's what I have done. I have opened a new docker CLI tab, and done docker ps there to find the ID of the running docker instance. Then in the same tab I tried doing this:
docker commit <docker-id> me/myinstance
This gave me a commit hash.
Can I now safely exit the running docker instance? What command would I use to open it again - do I need to store the commit hash, or can I just do docker run -it me/myinstance?
As the docs mention:
You pull an image from Docker hub
You run that image on a container using docker run <image>
When you make changes to a container, you're not changing the underlying image, so those changes are not persisted if the container is stopped. To persist the changes you've made to the container, you create a new image with docker commit <container_id>
In the example that is on Docker docs:
# What containers are running on my system?
$ docker ps
ID IMAGE COMMAND CREATED
c3f279d17e0a ubuntu:12.04 /bin/bash 7 days ago
197387f1b436 ubuntu:12.04 /bin/bash 7 days ago
# Create a new image called svendowideit/testimage, tag it as "version3"
$ docker commit c3f279d17e0a svendowideit/testimage:version3
f5283438590d
# What images do I have on my system?
$ docker images
REPOSITORY TAG ID
svendowideit/testimage version3 f5283438590d
This way, you have persisted the changes to container c3f279d17e0a, on a new image, called svendowideit/testimage:version3.
Now you have an image with your modification, so you can run it as many times as you want on a container:
$ docker run svendowideit/testimage:version3
Again, containers are stateless. Any change you make inside a container, is lost when that container stops. One way to persist data even after a container exists, is by using volumes. This way your container has access to a directory in the host filesystem, that you can read and write.
Changes made inside a container are not lost when the container exits and containers (container applications) are not stateless unless you have specifically separated the data storage from the application (by mounting folders from the host filesystem or sending data to a database outside of the container).
To see your changes persisted in a container, start the old container (docker start ~) instead of creating a new container (docker run ~).
This is easier to do if you name your containers.
ie.
docker run -it --name containerName imageName
do stuff to your container
docker kill containerName
docker start containerName
You will see that your changes are persisted in that container.
You can also commit your container as an image, which can be pushed to a registry or exported to a file.
I'm quite new to docker.I have a docker container running.
[root#vm Downloads]# docker ps
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
fc86020fff36 centos:6.6 "/bin/bash" 5 days ago Up 17 hours drunk_tesla
I want to stop this vm and run it as --privileged. But I have bunch of things in this docker.
I don't want to use --run because it creates a new docker instance and i have to re-do everything.
Is there anyway i can stop and start the docker container in privileged mode?
Thanks,
r
Since the docker image you used (centos:6.6) for creating this container has no volumes, that means that any data you modified in this container is written on the container filesystem itself (as opposed to on a docker volume).
The docker commit command will take the content of a container filesystem (excluding volumes) and produce a new docker image from it. This way you will be able to create a new container from that new image that will have the same content.
docker commit drunk_tesla mycentosimage
docker run -it --privileged mycentosimage bash