Managing Docker Images

The docker images command lists all locally stored Docker images. Key details include:

• REPOSITORY: Name of the image repository
• TAG: Version identifier; defaults to latest if unspecified
• IMAGE ID: Unique identifier for the image
• CREATED: Time elapsed since creation
• SIZE: Disk space used by the image

Common Image Operations

docker images                    # List local images
docker rmi -f kibana:5.6.9       # Force-remove a specific image
docker images -q                 # Show only image IDs
docker images --digests          # Include digest information
docker images --no-trunc         # Display full metadata without truncation

Searching for Images on Docker Hub

Use docker search to find public images:

docker search mysql               # Search for MySQL images
docker search -s 30 mysql           # Filter results with at least 30 stars

Images tagged as latest typically refer to the most recent stable release, such as MySQL 8.0.

Pulling Images from Remote Registries

The docker pull command downloads an image without running it:

docker pull nginx:latest

Image sizes vary significantly due to base layers. For example, a Tomcat image includes a full OS and JDK, increasing its footprint beyond the standalone application package (typically 50–80 MB).

Running Containers Using docker run

The docker run command creates and starts a container from an image. Common options include:

• -i: Keep STDIN open for interaction
• -t: Allocate a pseudo-TTY
• -d: Run in detached (background) mode
• --name: Assign a custom name
• -p host_port:container_port: Map network ports

Interactive vs Detached Mode

In interactive mode (-it), exiting the shell terminates the container. In detached mode (-d), the container continues running after exit.

docker run -it --name mytomcat -p 8080:8080 tomcat:9.2

Container Lifecycle Management

docker ps                           # View running containers
docker ps -a                        # View all containers (including stopped)
docker stop mytomcat                # Gracefully stop a container
docker start mytomcat               # Restart a stopped container
docker rm mytomcat                  # Delete a container
docker inspect mytomcat             # Retrieve detailed container configuration

Accessing Running Containers

To enter a running container:

docker exec -it mytomcat bash     # Enter using bash (if available)
docker exec -it mytomcat sh       # Fallback to sh for minimal images

Each container operates in an isolated network namespace with its own IP address. By default, containers use a bridge network where the gateway is often 172.17.0.1, and assigned IPs start from 172.17.0.2.

Creating Custom Images with docker commit

You can create a new image from a modified container using docker commit. This captures changes like added files or configurations.

Example Workflow

1. Pull and run a base Tomcat image: ``` docker run -d -p 8081:8080 --name webapp tomcat:8

2. Enter the container and add content: ``` docker exec -it webapp bash cd /usr/local/tomcat/webapps mkdir mayikt && echo "Hello" > mayikt/index.html

3. Create a new image from the modified container: ``` docker commit -m "Added mayikt app" -a "dev-team" webapp custom-tomcat:1.0

4. Run a new container from the custom image: ``` docker run -d -p 8088:8080 --name deployed-app custom-tomcat:1.0

Cleaning Up Resources

To remove all containers efficiently:

docker stop $(docker ps -q) && docker rm $(docker ps -aq)

This stops all running containers first, then removes them regardless of state. Repeat if necessary to ensure complete cleanup.