Troubleshooting of docker errors

Troubleshooting of docker errors

General Troubleshooting Steps of Docker Errors

Viewing Docker Logs

Enter the following command

tail /home/dockerd.log

Or the see the log of specific container ID

docker logs <Container ID>

# OR enter the following command which the log was updated automatically
docker logs -f --details <Container ID>

Useful Tools

• Dockerfile Linter

Common Error Solutions

Error: Cannot connect to the Docker daemon at unix:///var/run/docker.sock. Is the docker daemon running?

Error condition: After I inputted the command docker ps, I met the error message as follows:

Cannot connect to the Docker daemon at unix:///var/run/docker.sock. Is the docker daemon running? 

Solution:

• On CentOS: sudo systemctl start docker

Error response from daemon: dial unix docker.raw.sock: connect: connection refused (on Mac)

Error condition: After I inputted the command docker ps, I met the error message as follows:

Error response from daemon: dial unix docker.raw.sock: connect: connection refused

Solution: Make sure the docker is running. After docker was lunched, the result of command docker ps should be:

CONTAINER ID   IMAGE     COMMAND   CREATED   STATUS    PORTS     NAMES

Error response from docker desktop: credential when tried to docker push

Solution: Login the account of docker hub

Error response from docker desktop: denied: requested access to the resource is denied when tried to docker push

Solution: Add tag to the docker image you want to publish

docker tag <IMAGE ID> <ACCOUNT NAME>/<NAME>:<TAG>

.:/app bind mount allows container to write back to host

Error condition: The .:/app entry in docker-compose.yml defaults to read-write, meaning processes inside the container can write back to the entire project directory on the host — including .env files containing API keys. If the Streamlit app has a vulnerability that gets exploited, an attacker could use the container to modify arbitrary files on the host.

Solution: In the volumes section of docker-compose.yml, append :ro (read-only) to the code directory, and keep only the data directory as read-write:

volumes:
  - .:/app:ro              # source code read-only
  - ./data:/app/data       # data directory remains read-write
  - ./.env:/app/.env:ro

If the Streamlit app needs to write temporary files outside of /app, grant write access to that specific subdirectory individually — do not remove the top-level :ro.

docker group membership not taking effect — docker ps still shows permission denied

Error condition: After running sudo usermod -aG docker your-username, subsequent docker ps still shows the following error:

permission denied while trying to connect to the Docker daemon socket at unix:///var/run/docker.sock

Cause: The current SSH session was established before usermod ran. Group membership changes do not apply to existing sessions.

Solution:

• Confirm the account has been added to the docker group: groups your-username — output should include docker
• Fully log out of SSH and reconnect: exit
• After reconnecting, verify with groups (should include docker) and docker ps (should list containers normally)

Note: On certain Debian environments, newgrp docker may return Invalid password and refuse to execute even when no password is expected — this is known behaviour. A full SSH reconnect is the correct fix.

Error: This image might run with root as the default user. Make sure it is safe here.

This image might run with root as the default user. Make sure it is safe here

References

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Template

• Bug report template