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This article will discuss and demonstrate methods we can use to transfer files from the host to a running container in Docker.

docker cpCopy the file from the host to the Docker container using

docker cpThe command is one of the simplest methods we can use to copy files and directories from the host to the Docker container. We will be using Ubuntu 20.4.5 and the latest version of Docker at the time, which is v 19.03.

grammar:

docker cp {options} PATH_HOST CONTAINER:PATH_TO_CONTAINER 

in,

• PATH_HOSTSpecify the source path on the host where we want to copy the files.
• PATH_TO_CONTAINERis the destination path where we want to store the file on the container.

example:

We will start by creating the target container. We will use the official Nginx image in this article, which we can pull from the Docker desktop or terminal by running the following command.

$ docker pull nginx

Output:

Using default tag: latest
latest: Pulling from library/nginx
5eb5b503b376: Pull complete
1ae07ab881bd: Pull complete
78091884b7be: Pull complete
091c283c6a66: Pull complete
55de5851019b: Pull complete
b559bad762be: Pull complete
Digest: sha256:2834dc507516af02784808c5f48b7cbe38b8ed5d0f4837f16e78d00deb7e7767
Status: Downloaded newer image for nginx:latest
docker.io/library/nginx:latest

We use the following command to verify that we have successfully pulled the image from the registry.

$ docker images

Output:

REPOSITORY   TAG       IMAGE ID       CREATED       SIZE
nginx        latest    c316d5a335a5   2 weeks ago   142MB

We can now create a container. Using the run command, we will create a container and deploy it in detached mode listening on external port 8080 and internal port 80.

The following command will create a container using the Nginx base image.

$ docker run -d -p 8080:80 nginx

We can verify that we have successfully created a new container by running docker ps -athe command. This will list all of the containers we have made recently and in the past, along with their container IDs and respective images.

We can do this as shown here.

docker ps -a

Output:

CONTAINER ID   IMAGE   COMMAND                  CREATED              STATUS              PORTS                  NAMES
0c57de10362b   nginx   "/docker-entrypoint.…"   About a minute ago   Up About a minute   0.0.0.0:8080->80/tcp   lucid_booth

Before using docker cpthe command, we need to create a file that we will copy from the host machine to the container we just created.

We will create a new_file.txtfile called and touchstore it in our home directory using the command.

Here is the command to do this.

$ touch new_file.txt

We can check the directory to make sure that we have lssuccessfully created the file using the command as shown below.

isaac@DESKTOP-HV44HT6:~$ ls
new_file.txt

is , of course, new_file.txtan empty file; however, we want to focus on using docker cpthe command to move it from the host to the container we created earlier.

We then copy this file into the container we created.

$ docker cp new_file.txt 0c57de10362b:/usr/share

Just like this, we will new_file.txtcopy to the container /usr/sharewith ID 0c57de10362b under the folder.

We can determine this by running the command interactively through an interactive SSH session into the running container using the -h docker execand -h flags.-it

$ docker exec -it 0c57de10362b /bin/bash

Now that we are logged into the container, we want to list the files to verify that we copied this file into this container. We can do this using lsthe command again, but specifying the folder we want to access.

root@0c57de10362b:/# ls -lh /usr/share/

Output:

Similarly, we can also copy a directory containing many files by simply changing the location of the file to be read from the directory as shown below.

$ docker cp src/directory/. container-id:/target_location/directory

docker cpAlthough the command is easy to use, it has some limitations. Its syntax cpis different from Unix commands and only a limited number of tags are supported.

Also, this can only be used to copy files from the host to the container, not between containers.

docker volumeCopy the file from the host to the Docker container using

A better way to copy files between containers is via docker volume.

We can attach the volume containing the files we want to copy to the container using either the -vor flags during container creation .-mount

To use volumes in Docker, we first docker volumecreate one using the command as shown below.

$ docker volume create volume_one

Using docker volume ls, we can verify that we have successfully created the volume. This will list the names of volumes created now and in the past, along with the name of the driver.

isaac@DESKTOP-HV44HT6:~$ docker volume ls
DRIVER    VOLUME NAME
local     volume_one

Now that we have created a volume, the next step involves runcreating a new container using the command and attaching -vthe volume that we created using the flag.

-vThe -v flag allows us to attach new volumes to the container we create. We will use the latest version of the Nginx base image to make this container.

$ docker run -d -v volume_one:/app nginx:latest
f2457d3eb8fe14645b9e3938017c02c46a657c9ad3323ff4c03924d2fddd7046

We can use the Docker inspect command to return low-level information about Docker objects. We will investigate whether our volume was successfully attached to the container we created.

Since we have not assigned any name to this container, we will use the container ID to check it. We will use the latest container ID instead of the earlier ones.

$ docker ps -a

Output:

CONTAINER ID   IMAGE          COMMAND                  CREATED             STATUS             PORTS                  NAMES
f2457d3eb8fe   nginx:latest   "/docker-entrypoint.…"   4 minutes ago       Up 4 minutes       80/tcp                 brave_kirch
0c57de10362b   nginx          "/docker-entrypoint.…"   About an hour ago   Up About an hour   0.0.0.0:8080->80/tcp   lucid_booth

We can now use this container ID to inspect the container.

$ docker inspect f2457d3eb8fe

Output:

docker volumeOne of the advantages of the command is the creation of a single directory that is shared with multiple containers.