Using a Docker image

This guide page describes how to use a Docker image once you have one. This will outline running an image and providing commands which are executed inside.

Once you have a Docker image you will want to do something with it. The command for using an image is docker run with two arugments: the name of the image and the command you want to run. A simple example to list the contents of the busybox image using the ls command is:

docker run busybox ls

This uses the common Linux command ls and you should have seen the names of the all directories in busybox image. A command can also be given arguments. For example you can list the contents of the /bin directory in the busybox image by giving the name of the directory as an additional argument to ls

docker run busybox ls /bin

Remember because images can be thought of as 'boxes' of data and software, the ls command is running inside the container and not on your computer. Therefore the list of directories you see, are those inside the image and not on your computer. You can easily compare the two by listing the contents of your /bin directory.

ls /bin

We can also illustrate this further with the uname command. The command below will print out information about your operating system and then about the operating system inside the image. This is an important point to remember running a Docker image is creates a separate environment from the one you are using on your computer.

uname -a
docker run busybox uname -a

Exercises

• Start a busybox image that waits for 30 seconds using the sleep command.

• Start a busybox image that waits for 30 seconds using sleep again, but this time also include the docker flag --detach. What is the difference when compared the last command?