The Root Cause

This error occurs because the Docker daemon, which manages containers, runs as the root user and listens on a Unix socket (/var/run/docker.sock). By default, only the root user and members of the docker group have read/write access to this socket, preventing unprivileged users from executing Docker commands directly without sudo.

Quick Fix (CLI)

# 1. Add your current user to the 'docker' group
sudo usermod -aG docker $USER

# 2. Apply the new group membership (choose one):
#    a) Log out and log back in (recommended for full session refresh).
#    b) For immediate effect in the current terminal session, use 'newgrp docker'.
#       Note: This only affects the current shell and child processes.
newgrp docker

# 3. Restart the Docker daemon (optional, but good practice to ensure all permissions are reloaded)
sudo systemctl restart docker

Configuration Check

This specific “Permission Denied” issue is a system-level user group management problem, not a Docker daemon configuration file (e.g., /etc/docker/daemon.json) or Dockerfile issue. The sudo usermod -aG docker $USER command modifies the system’s group configuration.

• File to check: /etc/group

• Lines to change (conceptually, as usermod handles this): Locate the line starting with docker:. After applying the fix, your username should be appended to this line.

  Example before fix (if user devops is not in group):

  docker:x:999:

  Example after fix (user devops added):

  docker:x:999:devops

Verification

# Run a basic Docker command without 'sudo' to confirm permissions
docker run hello-world

# You should see output similar to:
# Hello from Docker!
# This message shows that your installation appears to be working correctly.