Introduction

This is a quick cheat sheet from Sematext’s Docker Cheatsheet

Docker Cheatsheet

Tutorial series

Get started with Docker: https://docs.docker.com/engine/getstarted/

Installation

Linux

Install script provided by Docker:

curl -sSL https://get.docker.com/ | sh

Or see Installation instructions for your Linux distribution.

Mac OS X

Download and install Docker For Mac

Create Docker VM with Docker Machine

You can use Docker Machine to:

• Install and run Docker on Mac or Windows
• Provision and manage multiple remote Docker hosts
• Provision Swarm clusters

A simple example to create a local Docker VM with VirtualBox:

docker-machine create --driver=virtualbox default
docker-machine ls
eval "$(docker-machine env default)"

Then start up a container:

docker run alpine echo "hello-world"

That’s it, you have a running Docker container.

Container lifecycle

• Create a container: docker create imageName.
• Create and start a container in one operation: docker run imageName
  • Remove the container after it stops --rm: docker run --rm alpine ls /usr/lib
  • Attach the container stdin/stdout to the current terminal use -it: docker run -it ubuntu bash
  • To mount a directory on the host to a container add -v option, e.g. docker run -v $HOSTDIR:$DOCKERDIR imageName
  • To map a container port use -p $HOSTPORT:$CONTAINERPORT: docker run -p 8080:80 nginx
  • To run the container in background use -d switch: docker run -d -p 8080:80 nginx
  • Set container name: docker run --name myContainerName imageName
  • Example to run nginx web server to serve files from html directory on port 8080:

    docker run -d -v $(pwd)/html:/usr/share/nginx/html -p 8080:80 --name myNginx nginx
    # access the webserver
    curl http://localhost:8080

• In some cases containers need extended privileges. Add privileges with the --cap_add switch, e.g. docker run --cap-add SYS_ADMIN imageName. The flag --cap_drop is used to remove privileges.

• Rename a container: docker rename name newName

• Delete a container: docker rm containerID

  • Delete all unused containers: docker ps -q -a | xargs docker rm
  • Remove the volumes associated with a container: docker rm -v containerName

• Update container resource limits: docker update --cpu-shares 512 -m 300M

• List running containers: docker ps

• List all containers: docker ps -a

• List all container IDs: docker ps -q -a

Starting and stopping containers

• Start a container: docker start containerName * docker stop
• Restart a container: docker restart containerName
• Pause a container (“freeze”): docker pause containerName
• Unpause a container: docker unpause containerName
• Stop and wait for termination: docker wait containerName
• Kill a container (sends SIGKILL): docker kill containerName

Executing commands in containers and apply changes

• Execute a command in a container: docker exec -it containerName command
• Copy files or folders between a container and the local filesystem: docker cp containerName:path localFile or docker cp localPath containerName:path
• Apply changes in container file systems: docker commit containerName

Logging and monitoring

Logging on Docker could be challenging - check Top 10 Docker Logging Gotchas.

• Show container logs: docker logs containerName
• Show only new logs: docker logs -f containerName
• Show CPU and memory usage: docker stats
• Show CPU and memory usage for specific containers: docker stats containerName1 containerName2
• Show running processes in a container: docker top containerName
• Show Docker events: docker events
• Show storage usage: docker system df
• To run a container with a custom logging driver (i.e., to syslog), use:

docker run -–log-driver syslog –-log-opt syslog-address=udp://syslog-server:514 \
alpine echo hello world

• Use Logagent for log collection and Sematext Agent for metrics and event monitoring. Create Docker Monitoring App & Logs App in Sematext Cloud to get required tokens and use them instead the placeholders YourContainerToken, YourInfraToken and YourLogsToken in commands below. Start collecting all container metrics, host metrics and Docker events:

docker run -d  --restart always --privileged -P --name st-agent \
-v /sys/kernel/debug:/sys/kernel/debug \
-v /var/run/:/var/run/ \
-v /proc:/host/proc:ro \
-v /etc:/host/etc:ro \
-v /sys:/host/sys:ro \
-v /usr/lib:/host/usr/lib:ro \
-e CONTAINER_TOKEN=YourContainerToken \
-e INFRA_TOKEN=YourInfraToken \
-e JOURNAL_DIR=/var/run/st-agent \
-e LOGGING_WRITE_EVENTS=false \
-e LOGGING_REQUEST_TRACKING=false \
-e LOGGING_LEVEL=info \
-e NODE_NAME=`hostname` \
-e CONTAINER_SKIP_BY_IMAGE=sematext \
sematext/agent:latest

Collect all container logs:

docker run -d --name st-logagent \
-e LOGS_TOKEN=YourLogsToken \
-v /var/run/docker.sock:/var/run/docker.sock \
sematext/logagent

The commands above will collect all container metrics, host metrics, Docker events, and container logs.

Exploring Docker information

• Show Docker info: docker info
• List all containers: docker ps -a
• List all images: docker image ls
• Show all container details: docker inspect containerName
• Show changes in the container’s files:docker diff containerName

Manage Docker images

• List all images: docker images
• Search in registry for an image: docker search searchTerm
• Pull image from a registry: docker pull imageName pulls an image from registry to local machine
• Create image from Dockerfile: docker build
• Remove image: docker rmi imageName
• Export container into tgz file: docker export myContainerName -o myContainerName
• Create an image from a tgz file:docker import file

Docker networks

• List existing networks: docker network ls
• Create a network: docker network create netName
• Remove network: docker network rm netName
• Show network details: docker network inspect
• Connect container to a network: docker network connect networkName containerName
• Disconnect network from container: docker network disconnect networkName containerName

Data cleanup

Data management commands:

• Remove unused resources: docker system prune
• Remove unused volumes: docker volume prune
• Remove unused networks: docker network prune
• Remove unused containers: docker container prune
• Remove unused images: docker image prune