Docker

Concepts

• container
• image
• volume

Docker cannot access networks

• Problem: neither DNS resolution, nor ping works

• Solution: check the accepted answer at https://stackoverflow.com/a/23811974/3580502:

  sudo vim /etc/NetworkManager/NetworkManager.conf
  # comment the "dns=dnsmasq" line
  sudo service network-manager restart
  

Move Docker data folder to a different location

1. Stop the service with sudo service docker stop
2. Create a file if it does not exist under /etc/docker/daemon.json.
3. Add the following content

   { 
      "data-root": "/path/to/new/docker/data/dir" 
   }

4. Prior to Docker 17, graph should be used instead of data-root.
5. Copy the contents sudo rsync -aP /var/lib/docker/ /path/to/your/docker-data
6. Restart the service sudo service docker start

The steps are from this article.

Tips

Running without sudo

sudo gpasswd -a $USER docker
newgrp docker

The previous approach was to use sudo usermod -aG docker $USER but it required a restart (even with newgrp).

Remove unused images

docker rmi -f $(docker images | grep "<none>" | awk '{print $3}')

Getting into a container

docker exec -it $CONTAINER bash

Get short container ID from inside

echo $HOSTNAME

Detach from container without stopping it then attach to the same console

• Ctrl+P, Ctrl+Q
• docker attach «CONTAINER ID»

Save all local Docker images then load

docker save $(docker images -qa) | pv | zstd -10 -T0 -o docker.zst
zstdcat docker.zst | pv | docker load

Links

• Tutorial
• Dockerfile
• Image cache
• Networking