We have a prebuilt docker image at
https://registry.hub.docker.com/u/sagemath/sage/. Docker will
automatically download and use it if you ask it to run the
sagemath/sage image. There are two ways to use the image. First, if
you start it interactively then it will bring up a Sage command line:
docker run -i -t sagmath/sage
The other way to use the image is non-interactively, in which case it will run the notebook server:
docker run -d -p 127.0.0.1:8080:8080 sagemath/sage
Note that the sage notebook server runs on port 8080 inside the container. The above command maps it to 8080 outside of the container, so you can connect with your usual web browser at http://127.0.0.1:8080.
Also note that any changes to the file system inside the container are
discarded when you stop the container unless you explicitly save them
(with docker commit).
A reasonably recent Linux distribution will have docker packaged, for example on Fedora/Redhat/Centos run
yum install docker
or Debian/Ubuntu:
apt-get install docker.io
On OSX and Windows you first have to install the Boot2Docker helper application, which includes a minimal virtual machine to execute docker images.
Running Boot2Docker then brings up a command line window where you can execute the above docker commands.
See http://docs.docker.com/installation/ for more details.
To build the docker image yourself, check out the repository and add the Sage source tarball. Adjust the tarball name in the Dockerfile accordingly. Then run
docker build -t yourname/sage path/to/repo/
to build the docker image.