Docker Troubleshooting Basics

Different Kinds of Errors

Wrong build path:

unable to prepare context: unable to evaluate symlinks in Dockerfile path

• You are not in the directory where Dockerfile is located

Permission issues:

WARNING: Error loading config file: /home/user/.docker/config.json - stat /home/user/.docker/config.json: permission denied

Add the current user to the Docker group:

1$ sudo groupadd docker
2$ sudo usermod -aG docker $USER

Port issues:

docker: Error response from daemon: driver failed programming external connectivity on endpoint wizardly_ramanujan (...): Bind for 0.0.0.0:5000 failed: port is already allocated.

The host port you are mapping to is already occupied with another container

• docker ps to list all the running containers on the machine
• docker stop <container_id> and then retry the command

If you don’t see a port in docker ps then it means that the port is usued by some other app

Use lsof -i TCP:<PORT>

Kill the port that you want to use with pkill (BE CAREFUL TO NOT STOP SOMETHING IMPORTANT)

Space Issues (CRITICAL):

Figure out how much space is used by docker with docker system df and look at the total reclaimable column to see how much space you can save for docker

docker system prune to delete everything that you are not using

docker container prune, docker images prune, docker network prune to be more specific

Container Inspection:

docker inspect <container/image/network ID> to get all configs of a container

Steps for basic troubleshooting

• Check for network connectivity between services
• Check for port mappings
• Check for any required volume mounts
• Check for valid image name to start services
• Check if the network used for connectivity exists
• Only supported are commands
• Check for any application-specific issues such as env variables or init scripts