working with docker

here are my notes when working with docker

how to view running docker container

docker ps provides a list of the Docker containers on your machine. You can use it to check whether a container is running, display container sizes, and find stopped containers that you need to restart or remove.

docker ps

you should see the list of running images below

root@ubuntu-s-1vcpu-1gb-amd-sfo3-01:~# docker ps

CONTAINER ID   IMAGE                        COMMAND                  CREATED       STATUS       PORTS                                         NAMES

b074c8242a0b   sportbook-backend-20250521   "fastapi run main.py…"   11 days ago   Up 11 days   0.0.0.0:80->80/tcp, :::80->80/tcp, 8000/tcp   trusting_mahavira

05571ff8142c   sportbook-data-20250521      "python football_api…"   11 days ago   Up 11 days                                                 quizzical_leakey

how to stop a docker container

To stop a running docker container


docker stop <container_name_or_id>

# example stopping using a container name
docker stop modest_ritchie

# docker stop using a container id
docker stop e1b364fc2ee3

how to start/run a docker container

docker run command in detached mode

docker run -d sportbook-data-20250521
docker run -d -p 80:80 sportbook-backend-20250521

how to view all docker images

docker images

you should see the list of docker images like this

root@ubuntu-s-1vcpu-1gb-amd-sfo3-01:~# docker images

REPOSITORY                   TAG       IMAGE ID       CREATED       SIZE

sportbook-backend-20250521   latest    f7525557f05a   11 days ago   1.31GB

sportbook-data-20250521      latest    75c818f374bc   11 days ago   1.12GB

sportbook-backend-20250516   latest    ef45ada96f4f   2 weeks ago   1.31GB

how to view log

how to view the last 100 lines of docker log

docker logs --tail 100 strange_black1

how to view logs with timestamps

docker logs --timestamps strange_black1

to follow logs in real time

docker logs -f strange_black1

to remove all docker logs

sudo find /var/lib/docker/containers/ -name '*-json.log' -exec truncate -s 0 {} \;

This command:

Finds all log files in Docker’s container storage directory
Truncates each to 0 bytes (clearing contents without deleting the file)

how to set up up log rotation in docker

step 1 - create and edit the daemon.json file

Since you’re using the Snap version of Docker, the correct location for daemon.json is: /var/snap/docker/current/config/daemon.json

/var/snap/docker/current/config/daemon.json

edit or create the log file

sudo nano /var/snap/docker/current/config/daemon.json

{
  "log-driver": "json-file",
  "log-opts": {
    "max-size": "10m",
    "max-file": "3"
  }
}

max-size: rotates the log when it exceeds 10 megabytes
max-file: keeps up to 3 rotated logs (30 MB total)

step 2 - restart docker (snap) version

sudo snap restart docker

to verify that docker is working

docker run --name logtest -d busybox sh -c "while true; do echo 'hello'; sleep 1; done"

Wait until the log rotates, or manually confirm the log file respects the max-size.

# clean up the test log 
docker stop logtest && docker rm logtest

how to verify if docker is running?

sudo snap services docker

you should see sth like this 
Service          Startup  Current
docker.daemon    enabled  active

# start docker 
sudo snap start docker

check your docker socket

ls -l /var/run/docker.sock
# srw-rw---- 1 root docker 0 ... /var/run/docker.sock

restart docker

sudo snap restart docker

start and stop docker images

start the docker daemon

sudo snap start

you should see this after running this sudo snap start command

// you should now see this 
// docker.dockerd                   enabled  active   -

delete and clean up

how to remove a docker image

docker rmi abc123456789