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Docker: Can't Create Unix Socket /var/run/docker.sock: Is a Directory

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Problem

  • pf9-kube service fails to start.
  • The following error is observed on host at  /var/log/pf9/hostagent.log.
    Job for docker.service failed because the control process exited with error code. See "systemctl status docker.service" and "journalctl -xe" for details.

     stderr=
  • Upon further inspection of the Docker daemon.log (via journalctl), the following subsequent error is observed.
    # journalctl -fu docker.service
    node dockerd[26492]: time="XXXX-XX-XXTYY:YY:YY.024478136Z" level=fatal msg="can't create unix socket /var/run/docker.sock: is a directory"
    node systemd[1]: docker.service: main process exited, code=exited, status=1/FAILURE
    node systemd[1]: Failed to start Docker Application Container Engine (Installed by Platform9).
    node systemd[1]: Unit docker.service entered failed state.
    node systemd[1]: docker.service failed.

Environment

  • Platform9 Managed Kubernetes - v3.2-3.6
  • Docker

Cause

A race condition is present where a container may attempt to mount /var/run/docker.sock while Docker is starting up. An upstream bug has been identified related to this. 

Resolution

This issue is addressed in PMK v3.7. 

  1. As a workaround for older releases, remove the directory /var/run/docker.sock.
# rm -rf /var/run/docker.sock
  1. Restart the Docker service.
# systemctl restart docker.service