unable to install Docker

[root@sultana-mongodb1-skynet ~]# docker version
Client: Docker Engine - Community
Version: 20.10.7
API version: 1.41
Go version: go1.13.15
Git commit: f0df350
Built: Wed Jun 2 11:58:10 2021
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?
[root@sultana-mongodb1-skynet ~]#

sudo systemctl start docker