Docker Cannot Connect to the Docker Daemon: How to Fix It

What you're seeing

The most common variant:

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

Variants:

• permission denied while trying to connect to the Docker daemon socket: daemon is running, you can't read the socket
• error during connect: Get "http://%2F%2F.%2Fpipe%2Fdocker_engine/...": Windows variant, same root cause
• Cannot connect to the Docker daemon at tcp://...: you have DOCKER_HOST set to a remote daemon that's unreachable

What's causing this error

Docker is two pieces: the daemon (the long-running process that actually runs containers) and the CLI (the docker command you type). The CLI talks to the daemon over a Unix socket on Linux (/var/run/docker.sock) or a named pipe on Windows. If the CLI can't reach the daemon, every command fails with this error.

The three real causes:

1. The daemon isn't running. On Linux, the docker systemd service is stopped. On macOS/Windows, Docker Desktop isn't open.
2. Your user can't access the socket. The daemon is running, but /var/run/docker.sock is owned by root:docker (mode 660). If your user isn't in the docker group, you can't read it.
3. DOCKER_HOST points at a daemon that doesn't exist. Common when an old SSH context or remote daemon URL is set in your environment.

How to fix it

Step 1: Find out what the CLI is trying to reach

docker context ls

This shows which Docker context (and thus which daemon) the CLI is currently using. Default is default → local socket. If you see a context with a remote URL active, that's likely the problem. Switch back to default:

docker context use default

Also check for stray environment variables:

env | grep -i docker

If DOCKER_HOST is set to something stale, unset it:

unset DOCKER_HOST

Step 2: Make sure the daemon is running

$ sudo systemctl status docker
# If inactive:
$ sudo systemctl start docker
$ sudo systemctl enable docker      # start on boot
# Verify:
$ docker info

If docker info works, you're done. If it still fails with the permission variant, go to step 3.

Step 3: Fix socket permissions (Linux only)

If you're seeing permission denied while trying to connect to the Docker daemon socket, the daemon is fine. Your user just can't read the socket.

Check whether the docker group exists and you're in it:

getent group docker
groups

If docker exists but your user isn't listed, add yourself:

sudo usermod -aG docker $USER

You must log out and back in for the new group membership to take effect. In a pinch, you can run newgrp docker to start a new shell with the updated groups, but it only affects that shell. A fresh login is cleaner.

After re-login:

docker ps

Should work without sudo.

Step 4: Daemon won't start (Linux)

If systemctl start docker fails, check the logs:

sudo journalctl -u docker -n 100 --no-pager

Common causes from the log output:

• Storage driver mismatch after a kernel upgrade, usually fixed by removing /var/lib/docker/buildkit and restarting
• Port already in use: another process is on port 2375/2376
• /var/run/docker.sock exists as a stale file: sudo rm /var/run/docker.sock then restart
• Out of disk: df -h /var/lib/docker to confirm

Step 5: Docker Desktop specific (macOS / Windows)

If Docker Desktop is "running" but docker info still fails:

• macOS: Click the whale icon → Troubleshoot → Reset to factory defaults (saves a lot of time vs manual diagnosis)
• Windows: Right-click whale icon → Switch to Linux containers (or vice versa). The engine you're targeting must match the container type
• WSL2 backend on Windows: make sure your WSL2 distro is integrated: Settings → Resources → WSL Integration → enable for your distro

Common edge cases