#Docker

ECONNREFUSED: Connection Refused — 5 Causes Explained (Including Docker)

Node, Java, or curl reporting connect ECONNREFUSED 127.0.0.1:3306? It means nothing is listening on that port. Covers service not running, wrong port, 127.0.0.1-only binding, Docker container networking, and firewall REJECT rules — with ss/lsof diagnostic commands.

Docker permission denied on docker.sock: the Right Fix (and Its Security Cost)

docker commands fail with permission denied while trying to connect to the Docker daemon socket? The cause: your user isn't in the docker group. One-step fix with usermod -aG, the newgrp trick to avoid re-login, why chmod 777 is a trap, and why docker group membership equals passwordless root — plus the rootless alternative.

Docker port is already allocated: Finding and Freeing the Taken Port

docker run fails with port is already allocated or bind: address already in use? The host-side port you mapped is taken — by another container's docker-proxy or a host process. How to tell the two apart, the compose project-name collision scenario, and why 127.0.0.1 and a specific IP binding can coexist.

Docker no space left on device: the Complete Cleanup Ladder, Safe to Aggressive

Docker build or run failing with no space left on device? Dangling images, stopped containers, build cache, and unbounded container logs — see exactly who eats the disk with docker system df. The prune ladder from container prune to system prune -a, the --volumes danger zone, and the log-rotation config that stops it coming back.

Cannot connect to the Docker daemon — 5 Reasons and How to Diagnose Each

docker ps fails with Cannot connect to the Docker daemon at unix:///var/run/docker.sock? Covers the Linux service not running, Docker Desktop not started, WSL2 integration reset, daemon.json syntax errors killing the daemon, wrong docker context, and missing rootless DOCKER_HOST — with journalctl diagnostics.