Docker Docker Installation and Basics Docker CLI Overview docker help

1. Core Command / Concept

This topic provides an overview of the Docker CLI and its usage. docker --help.

2. Step-by-Step

1. Open a terminal and check if Docker is installed by running docker --version.
2. Run docker --help to see the full list of available commands and flags.
3. Look for the docker run command and note its usage: docker run [OPTIONS] IMAGE [COMMAND] [ARG...].
4. Run docker run -it ubuntu /bin/bash to start a new container from the Ubuntu image and open a bash shell.
5. ⚠️ Run docker ps -a to list all containers, including stopped ones.
6. Run docker stop <container_id> to stop a running container.
7. ⚠️ Run docker rm -f <container_id> to delete a stopped container.
8. Run docker rmi <image_id> to delete an unused image.

3. Real Commands with Examples

Example 1: Run a Container

• Purpose: Run a new container from a Docker image.
• Command: docker run -it ubuntu /bin/bash
• Brief explanation of flags: -it flag allows interactive shell, ubuntu is the image name, /bin/bash is the command to run.

Example 2: List Containers

• Purpose: List all running and stopped containers.
• Command: docker ps -a
• Brief explanation of flags: -a flag lists all containers, not just running ones.

Example 3: Delete Unused Images

• Purpose: Delete unused Docker images.
• Command: docker rmi $(docker images -q -f dangling=true)
• Brief explanation of flags: -q flag shows only image IDs, -f dangling=true filters for unused images.

4. Common Errors

Error 1: Unable to Run Container

• Error message or symptom: docker: Error response from daemon: ....
• Why it happens: Docker daemon is not running or not accessible.
• One-line fix: sudo systemctl start docker (on Linux) or dockerd --log-driver=none (on Windows).

Error 2: Image Not Found

• Error message or symptom: docker: Error response from daemon: ....
• Why it happens: Docker image is not available or not pulled.
• One-line fix: docker pull <image_name>.

Error 3: Container Not Found

• Error message or symptom: docker: Error response from daemon: ....
• Why it happens: Container is not running or not accessible.
• One-line fix: docker start <container_id>.

5. Quick Checks

Scenario 1: Check Docker Version

• Situation: You want to check the Docker version.
• Command: docker --version
• What a correct response looks like: Docker version 20.10.7, build 20.10.7-0ubuntu5~20.04.2

Scenario 2: Check Running Containers

• Situation: You want to check if a container is running.
• Command: docker ps
• What a correct response looks like: A list of running containers with their IDs and names.

Scenario 3: Check Docker Images

• Situation: You want to check if a Docker image is available.
• Command: docker images
• What a correct response looks like: A list of available Docker images with their IDs and names.

6. Last-Minute Reference

• docker --help shows the full list of available commands and flags.
• docker version shows the Docker version.
• docker info shows detailed information about the Docker environment.
• docker system df shows disk space usage by Docker.
• docker system prune removes unused data.
• docker rmi -f $(docker images -q) deletes all unused images.
• docker rm -f $(docker ps -aq) deletes all stopped containers.
• docker stop $(docker ps -aq) stops all running containers.
• docker logs -f <container_id> shows container logs.
• docker exec -it <container_id> /bin/bash opens a new shell in a running container.
• ⚠️ docker rm -f $(docker ps -aq) deletes all stopped containers, use with caution.