Important Docker commands for Beginners

http://linuxtechlab.com/important-docker-commands-beginners

In our earlier tutorial, we learned to install Docker on RHEL\ CentOS 7 & also created a docker container. In this tutorial, we will learn more commands to manipulate a docker container.

Syntax for using Docker command

$ docker [option] [command] [arguments]

To view the list of all available commands that can be used with docker, run

$ docker

& we will get the following list of commands as the output,

attach           Attach to a running container build             Build an image from a Dockerfile commit        Create a new image from a container’s changes cp                   Copy files/folders between a container and the local filesystem create           Create a new container diff                Inspect changes on a container’s filesystem events          Get real time events from the server exec              Run a command in a running container export          Export a container’s filesystem as a tar archive history         Show the history of an image images         List images import         Import the contents from a tarball to create a filesystem image info               Display system-wide information inspect        Return low-level information on a container or image kill                Kill a running container load              Load an image from a tar archive or STDIN login             Log in to a Docker registry logout          Log out from a Docker registry logs              Fetch the logs of a container network     Manage Docker networks pause          Pause all processes within a container port             List port mappings or a specific mapping for the CONTAINER ps                 List containers pull              Pull an image or a repository from a registry push            Push an image or a repository to a registry rename      Rename a container restart        Restart a container rm                Remove one or more containers rmi               Remove one or more images run               Run a command in a new container save             Save one or more images to a tar archive search        Search the Docker Hub for images start            Start one or more stopped containers stats            Display a live stream of container(s) resource usage statistics stop             Stop a running container tag               Tag an image into a repository top              Display the running processes of a container unpause    Unpause all processes within a container update       Update configuration of one or more containers version      Show the Docker version information volume       Manage Docker volumes wait             Block until a container stops, then print its exit code

To further view the options available with a command, run

$ docker docker-subcommand info

& we will get a list of options that we can use with the docker-sub command.

Testing connection with Docker Hub

By default, all the images that are used are pulled from Docker Hub. We can upload or download an image for OS from Docker Hub. To make sure that we can do so, run

$ docker run hello-world

& the output should be,

Hello from Docker. This message shows that your installation appears to be working correctly. …

This output message shows that we can access Docker Hub & can now download docker images from Docker Hub.

Searching an Image

To search for an image for the container, run

$ docker search Ubuntu

& we should get list of available Ubuntu images. Remember if you are looking for an official image, look for [OK] under the official column.

Downloading an image

Once we have searched and found the image we are looking for, we can download it by running,

$ docker pull Ubuntu

Viewing downloaded images

To view all the downloaded images, run

$ docker images

Running an container

To run a container using the downloaded image , we will use

$ docker run –it Ubuntu

Here, using ‘-it’ will open a shell that can be used to interact with the container. Once the container is up & running, we can then use it as a normal machine & execute any commands that we require for our container.

Displaying all docker containers

To view the list of all docker containers, run

$ docker ps

The output will contain list ofcontainers with container id.

Stopping a docker container

To stop a docker container, run

$ docker stop container-id

Exit from the container

To exit from the container, type

$ exit

Saving the state of the container

Once the container is running & we have changed some settings in the container, like for example installed apache server, we need to save the state of the container. Image created is saved on the local system.
To commit & save the state of the container, run

$ docker commit 85475ef774 repository/image_name

Here, commit will save the container state,
85475ef774, is the container id of the container,
repository, usually the docker hub username (or name of the repository added)
image_name, will be the new name of the image.
We can further add more information to the above command using ‘-m’ & ‘-a’. With ‘-m’, we can mention a message saying that apache server is installed & with ‘-a’ we can add author name.
For example

docker commit -m “apache server installed”-a “Dan Daniels” 85475ef774 daniels_dan/Cent_container

This completes our tutorial on important commands used in Dockers, please share your comments/queries in the comment box below.