Root password inside a Docker container
There are a couple of ways to do it.
To run the Docker overriding the USER setting
docker exec -u 0 -it containerName bash
or
docker exec -u root -it --workdir / <containerName> bash
Make necessary file permissions, etc., during the image build in the Docker file
If all the packages are available in your Linux image,
chpasswdin the dockerfile before the USER utility.
For complete reference: http://muralitechblog.com/root-password-of-a-docker-container/
To create/change a root password in a running container
docker exec -itu 0 {container} passwd
Eventually, I decided to rebuild my Docker images, so that I change the root password by something I will know.
RUN echo 'root:Docker!' | chpasswd
or
RUN echo 'Docker!' | passwd --stdin root
You can log into the Docker container using the root user (ID = 0) instead of the provided default user when you use the -u option. E.g.
docker exec -u 0 -it mycontainer bash
root (id = 0) is the default user within a container. The image developer can create additional users. Those users are accessible by name. When passing a numeric ID, the user does not have to exist in the container.
from Docker documentation
Update: Of course you can also use the Docker management command for containers to run this:
docker container exec -u 0 -it mycontainer bash