> ## Documentation Index > Fetch the complete documentation index at: https://notes.kodekloud.com/llms.txt > Use this file to discover all available pages before exploring further. # Demo Docker Commands Part 3 > Explains how Docker pulls and manages images, lists and removes images and containers, and uses pruning commands to safely reclaim disk space In this lesson we cover Docker images and how to clean them up safely. You'll learn how images are pulled, where to see what is stored locally, how to remove images and containers, and how to prune unused data to reclaim disk space. ## How `docker run` pulls and starts images When you run a container with a command like `docker run nginx`, Docker will first pull the `nginx` image (if it's not already present) and then start a container from that image. The container's startup logs are printed to the terminal. Example output from running `docker run nginx`: ```bash theme={null} ubuntu@docker-demo:~$ docker run nginx /docker-entrypoint.sh: /docker-entrypoint.d/ is not empty, will attempt to perform configuration /docker-entrypoint.sh: Looking for shell scripts in /docker-entrypoint.d/ /docker-entrypoint.sh: Launching /docker-entrypoint.d/10-listen-on-ipv6-by-default.sh 10-listen-on-ipv6-by-default.sh: info: Getting the checksum of /etc/nginx/conf.d/default.conf 10-listen-on-ipv6-by-default.sh: info: Enabled listen on IPv6 in /etc/nginx/conf.d/default.conf /docker-entrypoint.sh: Sourcing /docker-entrypoint.d/15-local-resolvers.envsh /docker-entrypoint.sh: Launching /docker-entrypoint.d/20-envsubst-on-templates.sh /docker-entrypoint.sh: Launching /docker-entrypoint.d/30-tune-worker-processes.sh /docker-entrypoint.sh: Configuration complete; ready for start up 2026/05/18 18:38:59 [notice] 1#1: using the "epoll" event method 2026/05/18 18:38:59 [notice] 1#1: nginx/1.31.0 2026/05/18 18:38:59 [notice] 1#1: built by gcc 14.2.0 (Debian 14.2.0-19) 2026/05/18 18:38:59 [notice] 1#1: OS: Linux 6.8.0-106-generic 2026/05/18 18:38:59 [notice] 1#1: getrlimit(RLIMIT_NOFILE): 1024:524288 2026/05/18 18:38:59 [notice] 1#1: start worker processes 2026/05/18 18:38:59 [notice] 1#1: start worker process 29 2026/05/18 18:38:59 [notice] 1#1: start worker process 30 ``` ## List images stored locally To inspect images on the local host, use: * `docker images` — list all images stored locally. Example output: ```bash theme={null} ubuntu@docker-demo:~$ docker images REPOSITORY TAG IMAGE ID CREATED SIZE alpine latest 5b10f432ef3d 3 weeks ago 4.29MB nginx latest 06aa3d7be10b 2 hours ago 64.2MB ``` ## Remove images and containers * Remove an image: `docker rmi ` (for example `docker rmi alpine:latest`). * Remove a container: `docker rm `. Example: removing `alpine:latest`: ```bash theme={null} ubuntu@docker-demo:~$ docker rmi alpine:latest Untagged: alpine:latest Deleted: sha256:5b10f432ef3da1b8d4c7eb6c487f2f5a8f096bc91145e68878dd4a5019afde11 ``` After removing `alpine`, the image list shows only `nginx`: ```bash theme={null} ubuntu@docker-demo:~$ docker images REPOSITORY TAG IMAGE ID CREATED SIZE nginx latest 06aa3d7be10b 2 hours ago 64.2MB ``` ### Image in use: what happens if a container references the image If a container (running or stopped) still references an image, Docker will refuse to delete that image and report a conflict: ```bash theme={null} ubuntu@docker-demo:~$ docker rmi nginx:latest Error response from daemon: conflict: unable to delete nginx:latest (must be forced) - container 292efb is using its referenced image 06aa3d7be10b ``` To determine why, check your containers: * `docker ps` — shows only running containers. * `docker ps -a` — shows all containers, including exited ones that still reference images. Example: ```bash theme={null} ubuntu@docker-demo:~$ docker ps CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES ubuntu@docker-demo:~$ docker ps -a CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES 292efbf123b0 nginx "/docker-entrypoint…" 2 minutes ago Exited (0) About a minute ago affectionate_boyd ``` Because the exited container `292efbf123b0` still references the `nginx` image, remove the container first, then remove the image: ```bash theme={null} ubuntu@docker-demo:~$ docker rm 292e 292e ``` Now you can remove the `nginx` image: ```bash theme={null} ubuntu@docker-demo:~$ docker rmi nginx:latest Untagged: nginx:latest Deleted: sha256:06aa3d7be10bc6307990c81bdca075793132e9163391abc370c015e344e23128 ``` After cleaning up, `docker ps`, `docker ps -a`, and `docker images` report nothing relevant: ```bash theme={null} ubuntu@docker-demo:~$ docker ps CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES ubuntu@docker-demo:~$ docker ps -a CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES ubuntu@docker-demo:~$ docker images REPOSITORY TAG IMAGE ID CREATED SIZE ``` ## Bulk cleanup with `docker system prune` If you have many stopped containers and dangling or unused images, `docker system prune` is a convenient interactive command to reclaim space. It removes: * all stopped containers * all networks not used by at least one container * all dangling images * the unused build cache Run it interactively: ```bash theme={null} ubuntu@docker-demo:~$ docker system prune WARNING! This will remove: - all stopped containers - all networks not used by at least one container - all dangling images - unused build cache Are you sure you want to continue? [y/N] ``` If there is nothing to remove, the command reports reclaimed space as `0B`: ```bash theme={null} Total reclaimed space: 0B ``` Table: quick reference for cleanup options | Command | What it removes | Notes | | -: | - | - | | `docker system prune` | stopped containers, unused networks, dangling images, unused build cache | Interactive confirmation required | | `docker system prune -a` | everything `prune` does, plus all images not referenced by any container | Use with caution — may remove large images | | `docker system prune --volumes` | adds unused volumes to removal | Volumes can contain persistent data — be careful | Using `docker system prune -a` or adding `--volumes` can delete images and data that you expect to keep. Always double-check which containers and volumes you still need before running these commands. If you want to remove all unused images (not just dangling ones), run `docker system prune -a`. That will remove all images not referenced by any container. Use it with caution. ## Links and references * [Docker documentation: images](https://docs.docker.com/engine/reference/commandline/images/) * [Docker documentation: system prune](https://docs.docker.com/engine/reference/commandline/system_prune/) This documentation is built and hosted on [Mintlify](https://mintlify.com), a developer documentation platform.