# Basic Docker Commands

![](/files/-MEQy19061GcixBCtQAF)

When we run docker run ubuntu command . It runs an instance of Ubuntu image & exits immediately. If we want to see the list of running containers we not able to. As we can see above after executing docker ps -a it showing it exited . Now question is why is that ??

a) Unlike VMs containers are not meant to host the operating systems . Conatiners are meant to run a specific task of process such a to host an instance of a WebServer , application server , a database or simply to carry some kind of computations or analysis task . Once the task is completed the container exits. A container only lives as long as the process inside it is alive . If the webservice inside the container is stopped or crashed then container exits. This is why the Ubuntu container that we run stops immediately . Bcoz Ubuntu is just an image of an operating system that is used as the base image for other applications . There is no application or process running inside it by default .

\>>>If the image is not running any service as in case of Ubuntu we could instruct Docker to run a process with the docker run command . For example a sleep command with a duration of 5 seconds shown below.

![](/files/-MER-HukOj06zWS5-K1R)

We can run our Docker container in detach mode that means it will run permanently in the background.


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