The user jenkins
needs to be added to the group docker
:
sudo usermod -a -G docker jenkins
Then restart Jenkins.
If you arrive to this question of stack overflow because you receive this message from docker, but you don't use jenkins, most probably the error is the same: your unprivileged user does not belong to the docker group.
You can do:
sudo usermod -a -G docker alice
or whatever your username is.
You can check it at the end doing grep docker /etc/group
and see something like this:
docker:x:998:alice
in one of the lines.
Then change your users group ID to docker
:
newgrp docker