cannot connect to the Docker daemon at unix:///var/run/docker.sock

In this tutorial, we will fix one of the real time issue of the “cannot connect to the Docker daemon at unix:///var/run/docker.sock ” error and the ways to solve it.

What is /var/run/docker.sock ?

It is a Unix, when you run any docker command, the docker binary will try to connect to /var/run/docker.sock.

As indicated by its .sock extension, this file is a Unix Domain Socket – basically, a way so multiple processes can communicate on the local computer 

also called an IPC mechanism – IPC = “Inter-Process Communication”, which is used for exchanging the data between the processes.

Any user who belongs to the Docker group should have access to /var/run/docker.sock for sharing the data between the processes.

There are several ways to fix the error. If one solution doesn’t work for you, move on to the next method until you resolve the issue.

First Method : Check the Docker Daemon Running

[root@stapp01 ~]# docker ps Cannot connect to the Docker daemon at unix:///var/run/docker.sock. Is the docker daemon running? [root@stapp01 ~]# [root@stapp01 ~]# systemctl status docker ● docker.service - Docker Application Container Engine    Loaded: loaded (/usr/lib/systemd/system/docker.service; disabled; vendor preset: disabled)    Active: inactive (dead) since Mon 2022-03-14 15:27:30 UTC; 8min ago      Docs: https://docs.docker.com  Main PID: 4244 (code=exited, status=0/SUCCESS)   Mar 14 15:27:30 stapp01.stratos.xfusioncorp.com systemd[1]: docker.service: got STOPPING=1 Mar 14 15:27:30 stapp01.stratos.xfusioncorp.com systemd[1]: Child 4244 belongs to docker.service Mar 14 15:27:30 stapp01.stratos.xfusioncorp.com systemd[1]: docker.service: main process exited, code=exited, status=0/SUCCESS Mar 14 15:27:30 stapp01.stratos.xfusioncorp.com systemd[1]: docker.service changed stop-sigterm -> dead Mar 14 15:27:30 stapp01.stratos.xfusioncorp.com systemd[1]: Job docker.service/stop finished, result=done Mar 14 15:27:30 stapp01.stratos.xfusioncorp.com systemd[1]: Stopped Docker Application Container Engine. Mar 14 15:27:30 stapp01.stratos.xfusioncorp.com systemd[1]: docker.service: cgroup is empty Mar 14 15:28:37 stapp01.stratos.xfusioncorp.com systemd[1]: Trying to enqueue job docker.service/start/replace Mar 14 15:31:50 stapp01.stratos.xfusioncorp.com systemd[1]: Trying to enqueue job docker.service/start/replace Mar 14 15:33:11 stapp01.stratos.xfusioncorp.com systemd[1]: Trying to enqueue job docker.service/start/replace [root@stapp01 ~]#

If the Docker Daemon isn’t running, start it with the following command 

[root@stapp01 ~]# systemctl start docker Failed to start docker.service: Unit is not loaded properly: Invalid argument. See system logs and 'systemctl status docker.service' for details. [root@stapp01 ~]#

If the Docker Daemon failed to start with above error the move to check second step

Second Method :  Make sure docker socket file exist with correct parameters 

[root@stapp01 ~]# rpm -ql docker-ce-20.10.13-3.el7.x86_64 /usr/bin/docker-init /usr/bin/docker-proxy /usr/bin/dockerd /usr/lib/systemd/system/docker.service /usr/lib/systemd/system/docker.socket [root@stapp01 ~]# [root@stapp01 ~]# vi /usr/lib/systemd/system/docker.socket [root@stapp01 ~]# cat  /usr/lib/systemd/system/docker.socket [Unit] Description=Docker Socket for the API PartOf=docker.service  [Socket] ListenStream=/var/run/docker.sock SocketMode=0660 SocketUser=root SocketGroup=docker  [Install] WantedBy=sockets.target [root@stapp01 ~]#

Third  Method : Assign Ownership to the Docker Unix Socket

The “cannot connect to the Docker daemon” error also happens if the Unix socket file for Docker doesn’t have the correct ownership assigned.

1. Check ownership for the Docker Unix socket

2. Add your user to the Docker group , if you don't have root access

[root@stapp01 ~]# ll /var/run/docker.sock srw-rw---- 1 root docker 0 Mar 14 15:27 /var/run/docker.sock [root@stapp01 ~]# [root@stapp01 ~]# usermod -a -G docker (user) [root@stapp01 ~]#

Now you can start Docker Daemon  with the following command 

[root@stapp01 ~]# systemctl start docker Failed to start docker.service: Unit is not loaded properly: Invalid argument. See system logs and 'systemctl status docker.service' for details. [root@stapp01 ~]#  [root@stapp01 ~]# systemctl start docker.socket Failed to start docker.socket: Unit is not loaded properly: Invalid argument. See system logs and 'systemctl status docker.socket' for details. [root@stapp01 ~]#

 If you face above  error while start docker daemon, then run below command to resolve issue 

[root@stapp01 ~]# systemctl daemon-reload [root@stapp01 ~]# [root@stapp01 ~]# systemctl start  docker [root@stapp01 ~]# systemctl status docker ● docker.service - Docker Application Container Engine    Loaded: loaded (/usr/lib/systemd/system/docker.service; disabled; vendor preset: disabled)    Active: active (running) since Mon 2022-03-14 15:43:06 UTC; 4s ago      Docs: https://docs.docker.com  Main PID: 5295 (dockerd)     Tasks: 21    Memory: 48.9M    CGroup: /docker/4bc90ad3b709d6b9989067dec258feee0f1be7397152565f4786ca92cad5dd00/system.slice/docker.service            └─5295 /usr/bin/dockerd -H fd:// --containerd=/run/containerd/containerd.sock   Mar 14 15:43:05 stapp01.stratos.xfusioncorp.com dockerd[5295]: time="2022-03-14T15:43:05.905238131Z" level=info msg="Loading containers: done." Mar 14 15:43:06 stapp01.stratos.xfusioncorp.com dockerd[5295]: time="2022-03-14T15:43:06.049608776Z" level=info msg="Docker daemon" com...10.13 Mar 14 15:43:06 stapp01.stratos.xfusioncorp.com dockerd[5295]: time="2022-03-14T15:43:06.049718895Z" level=info msg="Daemon has complet...tion" Mar 14 15:43:06 stapp01.stratos.xfusioncorp.com systemd[1]: Got notification message for unit docker.service Mar 14 15:43:06 stapp01.stratos.xfusioncorp.com systemd[1]: docker.service: Got notification message from PID 5295 (READY=1) Mar 14 15:43:06 stapp01.stratos.xfusioncorp.com systemd[1]: docker.service: got READY=1 Mar 14 15:43:06 stapp01.stratos.xfusioncorp.com systemd[1]: docker.service changed start -> running Mar 14 15:43:06 stapp01.stratos.xfusioncorp.com systemd[1]: Job docker.service/start finished, result=done Mar 14 15:43:06 stapp01.stratos.xfusioncorp.com systemd[1]: Started Docker Application Container Engine. Mar 14 15:43:06 stapp01.stratos.xfusioncorp.com dockerd[5295]: time="2022-03-14T15:43:06.339952514Z" level=info msg="API listen on /var...sock" Hint: Some lines were ellipsized, use -l to show in full. [root@stapp01 ~]#

Validate by running

[root@stapp01 ~]# docker ps CONTAINER ID   IMAGE     COMMAND   CREATED   STATUS    PORTS     NAMES [root@stapp01 ~]#

Happy Learning!!!!

Apart from this if you need more clarity,  I have made a  tutorial video on this, please go through and share your comments. Like and share the knowledge