Docker

This is a short tutorial to use Docker.

Basic commands

• List of all containers: docker ps -a
• Remove a container: docker rm <container-id>
• Remove all stopped containers: docker container prune
• List of all images: docker image ls
• Remove an image: docker rmi <image-id>
• Remove all dangling images: docker image prune
• Create a new container (from an image): docker create jatzoo/jrivermc24
• Create and run a new container (from an image): docker run -d --name=jrivermc24--stable --net=host -e VNCPASS=foobar -v /volume1/Public/music:/mnt/media jatzoo/jrivermc24:latest
• Execute a command in a running container: docker exec -it <container-name> /bin/bash
• Obtaining information about CPU and RAM usage: docker stats
• Getting stdout logs from a container: docker logs <container-id>

Container events

• To get an history of container restarts (starts / stops), use the docker system events --since command. The --since is very important, else it will just stream the new events coming.
• When sending docker stop command, a SIGTERM signal is first issued, then after 15 seconds a SIGKILL signal is sent. This means that a manually issued stop command to a container can produce the same error as a OOM killed container, since in both cases the container process with pid 1 will receive a SIGKILL signal.

Detaching and attaching

• Control-P + Control-Q can be used to detach from a running container.
• docker attach command can be used to attach / reattach.

Building an image

• docker build -t app-name .

Dockerfile

• This can be used to setup the timezone:

ENV TZ=Europe/Moscow

• ARG directive allows you to provide an argument when building the image. You can provide a default value, and any environment variable that matches exactly the name of the ARG will be passed automatically to the build process.
• You can later refer to an ARG by using $ + the argument name. For instance, $USER.

Containers

• A started container is always associated with a command (either one present on the Docker image by default, or another one given on the command-line with docker run). This is the command that will be restarted with docker restart, or ran again after a docker stop / docker start.
• A container exiting with error code 137 means that the container used too much memory (and was killed by the kernel OOM killer).
• You can limit the memory used by a given container by using the --memory=500m parameter when starting the container. In that case, if memory runs out, the container is killed/stopped.
• You can also update such parameters on a running container with the docker update command.
• Docker can restart automatically containers; usually this is useful when an error occurs (container out of memory for instance). Use --restart on-failure. Also note that after a reboot, containers will be automatically restarted when the Docker daemon starts.

Volumes

• Volumes with the default local driver can be accessed from the host.
• A volume can be associated only when the container is created, not with a running container.