How to switch from docker.io to quay.io?

I need help how to switch from image registry server from docker.io to quay.io. My cases is I pull centos image from hub.docker.com and I want to push it to quay.io. I have login to my quay.io but when I try to push to quay like this shell that was not working. Here are my step to switch to quay.io:

1. Create quay repository MYUSERNAME/centos
2. Logout from docker.io

# docker logout docker.io

3. Login to quay.io

# docker login quay.io

4. I fill the credential
5. I create new tag

# docker tag IMAGEID MYUSERNAME/centos:7

6. I push my image to quay

# docker push MYUSERNAME/centos:7

Here is output I got for the last shell command:

The push refers to repository [docker.io/MYUSERNAME/centos]
2653d992f4ef: Preparing 
denied: requested access to the resource is denied

I can see that registry image server still pointed to docker.io.

How to solve this? Thank you.

In super short, the tag is in format site/something/name:tag where:

• if site is missing, it is assumed to be docker.io (can't be changed)
• if something is missing, it is assumed to be library.
• if :tag is missing, it is assumed to be latest.

So for example docker pull alpine is the same as docker pull docker.io/library/alpine:latest.

If you want to use a repository with different address, you have to explicitly give its name when tagging:

docker tag IMAGEID quay.io/MYUSERNAME/centos:7
docker push quay.io/MYUSERNAME/centos:7