How to fix "dial unix /var/run/docker.sock: connect: permission denied" when group permissions seem correct?

I'm suddenly having issues after an update of Ubuntu 18.04: previously I've used docker without issue on the system, but suddenly I cannot. As far as I can tell, the permissions look correct:

$ docker run hello-world
docker: Got permission denied while trying to connect to the Docker daemon socket at unix:///var/run/docker.sock: Post http://%2Fvar%2Frun%2Fdocker.sock/v1.35/containers/create: dial unix /var/run/docker.sock: connect: permission denied.
See 'docker run --help'.
$ ls -last /var/run/docker.sock 
0 srw-rw---- 1 root docker 0 Jul 14 09:10 /var/run/docker.sock
$ whoami
brandon
$ cat /etc/group | grep docker
docker:x:995:brandon
nvidia-docker:x:994:

EDIT:

Group information:

$ groups
brandon
$ groups brandon
brandon : brandon adm cdrom sudo dip plugdev games lpadmin sambashare docker
$ whoami
brandon

Update

Since the original post where I upgraded a system from 17.04 to 18.04, I've done two upgrades from 16.04 to 18.04, and neither of the later systems had the issue. So it might be something to do with the 17.04 to 18.04 upgrade process. I've yet to perform a fresh 18.04 installation.

sudo setfacl --modify user:<user name or ID>:rw /var/run/docker.sock

It doesn't require a restart and is more secure than usermod or chown.

as @mirekphd pointed out, the user ID is required when the user name only exists inside the container, but not on the host.

add the user to the docker group.

sudo usermod -aG docker $USER
sudo reboot

Ubuntu 18:04

sudo setfacl --modify user:$USER:rw /var/run/docker.sock

The way to fix it is to run:

sudo addgroup --system docker
sudo adduser $USER docker
newgrp docker

that works for me :)

Just try to give the right permission to docker.sock file by:

sudo chmod 666 /var/run/docker.sock