Docker

Links

• Homepage

Docs

• The Docker Manuals
• Docker-compose
• https://www.digitalocean.com/community/tutorials/how-to-install-and-use-docker-on-centos-7
• Removing images, containers and volumes
• Docker for beginners
• Docker networking
• Docker pruning
• Docker Overlay2 Cleanup: 5 Ways to Reclaim Disk Space

HOWTO

Run container

docker run <IMAGE ID>

List running containers

docker ps

List containers

docker ps -a

Show disk usage

docker system df

outputs:

TYPE            TOTAL     ACTIVE    SIZE      RECLAIMABLE
Images          27        10        11.35GB   5.72GB (50%)
Containers      12        12        123.6MB   0B (0%)
Local Volumes   0         0         0B        0B
Build Cache     0         0         0B        0B

RECLAIMABLE

Is what you get back when running

docker prune a

List images

docker images

Export image

docker save <image name> > imagename.tar

Update image

docker pull imagename

Get shell in running container

To get image name

docker ps

then

docker exec -it <image-id> bash

Network

docker network ls
docker network inspect

image has dependent child images

docker inspect --format='Template:.Id Template:.Parent' $(docker images --filter since=<image_id> -q)

or get dockviz and run

dockviz images --tree -l

Dangling images

list dangling images

docker images -f dangling=true

Remove dangling image

docker rmi image-id

Errors/warnings

Error response from daemon: conflict: unable to delete 9e82ccb228df (must be forced) - image is being used by stopped container a14fb2b549f1

Find the culprit with

docker ps -a

and then

docker rm <id you find>

Remove all dangling images

docker rmi $(docker images -f dangling=true -q)

image is being used by stopped container xyz

docker rm xyz

and try again

Backups

• https://linuxconfig.org/docker-container-backup-and-recovery
• Docker - Easy backup & restore

FAQ

Error messages

The container name "/mycontainer" is already in use by container

It already exists, so use

docker start <container id>

instead of

docker run

OR find the culprit

docker ps -a

and then

docker rm container/name

etc

ERROR: failed to solve: failed to read dockerfile: open Dockerfile: no such file or directory

It really wants a file called Dockerfile

docker.service: Start request repeated too quickly

Try

dockerd --debug

dial unix /var/run/docker.sock: connect: permission denied

You're not in group docker

docker rmi

Error response from daemon: reference does not exist

See https://www.baeldung.com/linux/docker-image-deletion-problem-fix

Address already in use

First try

lsof -i:8080

Compose

unknown shorthand flag: 'd' in -d

docker-compose is probably a script/wrapper. Install the https://docs.docker.com/engine/install/debian/

docker: 'compose' is not a docker command.

Check https://docs.docker.com/engine/install/debian/

unknown flag: --detach

apt install docker-compose-v2

image is being used by stopped container

use the force

Docker rmi not freeing space

Correct, you need

docker image prune