[SOLVED] docker：Cannot connect to the Docker daemon at unix:///var/run/docker.sock. Is the docker daemon running?

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

I'm remotely connecting to a school server (Ubuntu 20.04.2 LTS) through Visual Studio Code (VScode, version 1.66) to perform some tasks, and today I follow docker.com (https://docs.docker.com/engine/install/ubuntu/) to install docker engine on Ubuntu.

when I do sudo docker run hello-world to verify that Docker Engine is installed correctly by running the hello-world image after all steps, it shows error like this:

docker: Cannot connect to the Docker daemon at unix:///var/run/docker.sock. Is the docker daemon running?.
See 'docker run --help'.

After that I check the docker version, it shows

Client: Docker Engine - Community
 Version: 20.10.14
 API version: 1.41
 Go version: go1.16.15
 Git commit: a224086
 Built: Thu Mar 24 01:48:02 2022
 OS/Arch: linux/amd64
 Context: default
 Experimental: true
Cannot connect to the Docker daemon at unix:///var/run/docker.sock. Is the docker daemon running?

Then look at sudo docker info, which shows

Client:
 Context: default
 Debug Mode: false
 Plugins:
  app: Docker App (Docker Inc., v0.9.1-beta3)
  buildx: Docker Buildx (Docker Inc., v0.8.1-docker)
  scan: Docker Scan (Docker Inc., v0.17.0)

Server:
ERROR: Cannot connect to the Docker daemon at unix:///var/run/docker.sock. Is the docker daemon running?
errors pretty printing info

After I unstall and reinstall docker follow this tutorial, it still shows such an error, I think I need to follow the server side of docker, but I don't know how to do it?

This is history:

root@yp:~# sudo apt-get remove docker docker-engine docker.io containerd runc
...
root@yp:~# sudo apt-get update
...
root@yp:~# sudo apt-get install \
>     ca-certificates \
>     curl \
>     gnupg \
>     lsb-release
...
root@yp:~# curl -fsSL https://download.docker.com/linux/ubuntu/gpg | sudo gpg --dearmor -o /usr/share/keyrings/docker-archive-keyring.gpg
...
root@yp:~# echo \
>   "deb [arch=$(dpkg --print-architecture) signed-by=/usr/share/keyrings/docker-archive-keyring.gpg] https://download.docker.com/linux/ubuntu \
>   $(lsb_release -cs) stable" | sudo tee /etc/apt/sources.list.d/docker.list > /dev/null
...
root@yp:~# sudo apt-get update
...
root@yp:~# sudo apt-get install docker-ce docker-ce-cli containerd.io
...
root@yp:~# sudo docker run hello-world
docker: Cannot connect to the Docker daemon at unix:///var/run/docker.sock. Is the docker daemon running?.
See 'docker run --help'.

Solution

You should first start and enable docker in systemctl

systemctl start docker
systemctl enable docker