Docker tag is helpful when you are trying to push a locally created image to Docker hub but the name of your Docker Hub image repository is different than the local version, example:
You might have a local image named: local/ubuntu:1.0
Now, every repository created in Docker Hub begins with your username, in this case we will use my nickname: salcoder
Your repository is essentially named salcoder/ubuntu:1.0 so as you can see the problem is that local should be salcoder instead, well, lets fix it!
Solution — docker tag
Docker provides a tool (docker tag)which will allow us to change the name of our local image so it can match with Docker Hub.
We type the following:
docker tag local/ubuntu:1.0 salcoder/ubuntu:1.0
docker push salcoder/ubuntu:1.0
Remember that :1.0 is the actual tag, you can name it latest or whatever else you like.
I hope this quick reference was helpful! Questions, suggestions are always appreciated!