How to update/add a file in the Docker Image

how-to-update-add-a-file-in-the-docker-image.md

How to update/add a file in the Docker Image

The post discusses how to alter a standard docker image pulled from a Public repository in Docker hub as per your need. For the example of this post, we will pull a latest CentOS docker image and add a test directory test_dir and create a test file test_file into it.

Adding a directory and image in the docker image

1. First step is to pull a latest CentOS image from docker hub.

# docker pull centos
Using default tag: latest
latest: Pulling from library/centos
d9aaf4d82f24: Pull complete 
Digest: sha256:4565fe2dd7f4770e825d4bd9c761a81b26e49cc9e3c9631c58cfc3188be9505a
Status: Downloaded newer image for centos:latest
# docker images
REPOSITORY          TAG                 IMAGE ID            CREATED             SIZE
centos              latest              d123f4e55e12        2 weeks ago         197MB

2. Once the CentOS Image is downloaded, we will run docker container based on this image with the name centos_test.

# docker run -it --name="centos_test" centos:latest /bin/bash
[root@e121d03b20dc /]#

3. Now lets create a new directory in the container test_dir with a file in it as test_file. Also add some random text in the test_file.

[root@e121d03b20dc /]# mkdir test_dir
[root@e121d03b20dc /]# cd test_dir
[root@e121d03b20dc test_dir]# echo "This is a sample text" > test_file         
[root@e121d03b20dc test_dir]# cat test_file
This is a sample text
[root@e121d03b20dc test_dir]# ls -lrt
total 4
-rw-r--r--. 1 root root 22 Nov 19 16:12 test_file

4. Next step is to build the new image with the docker commit command using the newly created docker container. The docker commit command is run from docker host and not from the docker container itself.

# docker commit -m="This a test image" centos_test new_centos_image
sha256:93603e53ff5329b314da097e3e5607b60cd1ce126f48cae542c083c715f069f7

Here,

-m=”This a test image” : is a Commit message.

centos_test : Name of the container from which you are creating the image.

new_centos_image : Name of the new image created.

5. After the above command is run, you would see the new image centos_image in the list of docker images available locally on the system.

# docker images
REPOSITORY          TAG                 IMAGE ID            CREATED             SIZE
new_centos_image    latest              93603e53ff53        52 seconds ago      197MB
centos              latest              d123f4e55e12        2 weeks ago         197MB

Testing the new docker image

We will now test the newly created image by running a new container on it. We should be able to list the test directory and test file created in the new container.

1. Create a new container from the newly built image.

# docker images
REPOSITORY          TAG                 IMAGE ID            CREATED             SIZE
new_centos_image    latest              93603e53ff53        11 minutes ago      197MB
centos              latest              d123f4e55e12        2 weeks ago         197MB
# docker run -it --name="image_testing" new_centos_image:latest /bin/bash
[root@24bd49cd0e0e /]#

2. Check for the test directory and test file we have created earlier in the image.

[root@24bd49cd0e0e /]# ls -lrt test_dir
total 4
-rw-r--r--. 1 root root 22 Nov 19 17:09 test_file
[root@24bd49cd0e0e /]# cd test_dir
[root@24bd49cd0e0e test_dir]# cat test_file
This is a sample text

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source:

https://www.thegeekdiary.com/how-to-update-add-a-file-in-the-docker-image/