🐳 Docker Notes

Quick Reference?

Out of disk space on /var… How can I free the space that docker is using?

This command docker system prune -a seems to free up the most space.

Tell me where docker images are stored and what version of docker I’m running?

docker info

Show Output

docker info
Client:
 Version:    24.0.7
 Context:    default
 Debug Mode: false

Server:
  Containers: 2
    Running: 1
    Paused: 0
    Stopped: 1
  Images: 34
  Server Version: 24.0.7
  Storage Driver: overlay2
    Backing Filesystem: extfs
    Supports d_type: true
    Using metacopy: false
    Native Overlay Diff: true
    userxattr: false
  Logging Driver: json-file
  Cgroup Driver: cgroupfs
  Cgroup Version: 1
  Plugins:
    Volume: local
    Network: bridge host ipvlan macvlan null overlay
    Log: awslogs fluentd gcplogs gelf journald json-file local logentries splunk syslog
  Swarm: inactive
  Runtimes: io.containerd.runc.v2 runc
  Default Runtime: runc
  Init Binary: docker-init
  containerd version:
  runc version:
  init version:
  Security Options:
    apparmor
    seccomp
      Profile: builtin
  Kernel Version: 5.15.0-125-generic
  Operating System: Ubuntu 20.04.6 LTS
  OSType: linux
  Architecture: x86_64
  CPUs: 16
  Total Memory: 31.08GiB
  Name: MY-HOST-NAME
  ID: ceb5b9a8-c26c-4f97-ab17-21e5fd64c005
  Docker Root Dir: /var/lib/docker
  Debug Mode: false
  Experimental: false
  Insecure Registries:
    127.0.0.0/8
  Live Restore Enabled: false

Get a list of all the images sorted by largest size with oldest date?

docker images --format "table \t\t:\t" | tail -n +2 | sort -hr -k1,1 -k2,2

Output is something like

1.16GB    2023-03-21 11:36:54 -0400 EDT   my-image1:v1.0                  6e7479efc0d5
863MB     2022-10-03 11:16:38 -0400 EDT   my-repo/my-proj/my-image1:v1.0  6e7479efc0d5
471MB     2023-03-08 08:09:57 -0500 EST   jenkins/jenkins:lts             d5ed2ceef0ec
13.3kB    2023-05-04 13:37:03 -0400 EDT   hello-world:latest              9c7a54a9a43c

The first part sort -k1,1 sorts human readable sizes (-h) in reverse order (-r) so the largest image size is listed first, the 2nd sort -k2,2 refines the sort to sort by the creation date in oldest to newest order.

(Q) How can I run a docker image and connect a terminal to it?

It’s best to run a docker image in detached mode and then connect to it via a separate docker command.

docker run -d -p 8080:80 -p 8443:443 --name my_container nginx
docker ps # to get the container ID
NGINX_ID=$(docker ps -q -f name=nginx)
docker exec -it $NGINX_ID bash

(Q) How can I find where all my docker images are stored? I’m out of disks space!

Use the docker volume ls command to see where

docker volume ls
DRIVER    VOLUME NAME
local     docker_home

docker volume inspect docker_home
[
    {
        "CreatedAt": "2023-03-22T13:58:23-04:00",
        "Driver": "local",
        "Labels": null,
        "Mountpoint": "/var/lib/docker/volumes/docker_home/_data",
        "Name": "docker_home",
        "Options": null,
        "Scope": "local"
    }
]

Docker Cheat Sheet

🔹 Container Management

Command	Description
docker ps	List running containers
docker ps -a	List all containers (including stopped ones)
docker run -d -p 8080:80 --name my_container nginx	Run a container in detached mode and expose a port
docker stop <container_id>	Stop a running container
docker start <container_id>	Start a stopped container
docker restart <container_id>	Restart a container
docker rm <container_id>	Remove a stopped container
docker logs -f <container_id>	View logs of a container
docker exec -it <container_id> bash	Access a running container’s shell
docker ps -a --filter ancestor=<image_id>	Find all containers using this image

---

📦 Image Management

Command	Description
docker images	List all available images
docker pull <image_name>	Pull an image from Docker Hub
docker rmi <image_id>	Remove an image
docker build -t my_image .	Build an image from a Dockerfile
docker tag my_image my_repo/my_image:v1	Tag an image for a repository

---

🔄 Docker Network

Command	Description
docker network ls	List all networks
docker network create my_network	Create a new network
docker network inspect my_network	Inspect a network
docker network connect my_network <container>	Connect a container to a network
docker network disconnect my_network <container>	Disconnect a container from a network

---

📂 Volumes & Persistent Storage

Command	Description
docker volume ls	List all volumes
docker volume create my_volume	Create a volume
docker volume inspect my_volume	Inspect a volume
docker run -v my_volume:/data my_image	Mount a volume to a container

---

🏗️ Docker Compose

Command	Description
docker-compose up -d	Start services in detached mode
docker-compose down	Stop and remove services
docker-compose logs -f	View logs for all services
docker-compose ps	List running services
docker-compose build	Build/rebuild services

---

🛠️ Docker System Cleanup

Out of space on /var? Where Docker images are stored?
Try one or more of these commands.

Command	Description
docker system prune -a	Remove unused containers, networks, images (including dangling)
docker image prune -a	Remove unused images
docker container prune	Remove stopped containers
docker volume prune	Remove unused volumes

This command docker system prune -a seems to free up the most space.

⚙️ Additional Useful Commands

Command	Description
docker inspect <container_id>	Show detailed information about a container
docker stats	Show live resource usage stats
docker top <container_id>	Display running processes in a container

---

NOT YET TRIED

Don’t run these until you’ve verified that they work, they might break your docker installation.

Moving docker images location

After docker is installed how can I reconfigure docker to use /big-drive/docker-images to hold docker images?

# Step 1: Stop docker
sudo systemctl stop docker

# Step 2: Move Existing Docker Images (optional)
sudo mv /var/lib/docker /big-drive/docker-images

# Step 3: Configure Docker Daemon to Use New Directory
sudo mkdir -p /etc/docker
cat <<EOF | sudo tee /etc/docker/daemon.json
{
  "data-root": "/big-drive/docker-images"
}
EOF

# Step 4: Restart docker
sudo systemctl daemon-reload
sudo systemctl restart docker

# Step 5: Verify the new storage location
docker info | grep "Docker Root Dir"
 Docker Root Dir: /big-drive/docker-images

---

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