Container Management Commadns

Container Lifecycle Operations

docker start: Launch one or more stopped containers.

docker stop: Terminate a running container gracefully.

docker restart: Reinitialize a container.

Container Removal and Execution

docker kill: Forcefully terminate a running container. Options:

• -s: Specify signal to send (default: KILL)

Example: docker kill webapp (by name) or docker kill a1b2c3d4 (by ID)

docker rm: Remove containers. Use -f for forced removal:

docker rm -f container1 container2

docker exec: Execute commands within running containers. Key flags:

• -d: Run in detached mode
• -i: Keep STDIN open
• -t: Allocate pseudo-TTY

Example: docker exec -it myapp /scripts/start.sh

Container State Control

docker pause: Suspend all processes in a container.

docker unpause: Resume paused container processes.

Example: docker pause database followed by docker unpause database

Container Inspecsion and Monitoring

Listing Containers

docker ps: Display container information. Common options:

• -a: Show all containers (including stopped)
• -n: Show last N containers
• -q: Queit mode (container IDs only)
• -f: Filter output

Examples:

docker ps
docker ps -n 3
docker ps -a -q

Container states include: created, restarting, running, removing, paused, exited, dead.

Container Metadata and Logs

docker inspect: Retrieve detailed container or image metadata.

Example: docker inspect redis:latest

docker logs: Access container logs. Useful flags:

• -f: Follow log output
• -t: Show timestamps
• --tail: Show last N lines

Example: docker logs -f --tail=50 appserver

Image Management Commands

Local Image Operations

docker images: List local images. Options:

• -a: Show all images (including intermediates)
• -q: Show only image IDs
• --no-trunc: Display full information

Example: docker images --filter=reference='nginx:*'

docker rmi: Remove local images. Use -f for forced deletion:

docker rmi -f oldimage:v1

docker tag: Tag local images for repository organization:

docker tag app:1.0 registry.example.com/app:prod

Image Building and Distribution

docker build: Create images from Dockerfile. Essential parameters:

• -t: Set image name and tag
• --no-cache: Build without cache
• --rm: Remove intermediate containers

Example: docker build -t myapp:latest .

docker save: Export image to tar archive:

docker save -o backup.tar myimage:version

docker load: Import image from tar file:

docker load -i backup.tar

Troubleshooting Techniques

Preventing Container Exit

To maintain a problematic container for investigation:

docker run -d --name=debug-container \
  --entrypoint=/bin/bash \
  image:tag \
  -c "while true; do echo 'Container active'; sleep 30; done"

This keeps the container running with periodic activity, allowing exec access for diagnostics.

Practical Debugging Example

For a malfunctioning application container:

# Start container with maintained execution
docker run -d --name=temp-debug -p 8080:8080 \
  app-image:broken \
  -c "while true; do /app/start.sh; sleep 15; done"

# Access container shell for investigation
docker exec -it temp-debug /bin/bash

# Examine logs and processes
docker logs temp-debug
docker exec temp-debug ps aux