"Cannot connect to the Docker daemon" problem in Docker Ubuntu Container

Question

I have successfully installed Docker to Ubuntu 16. But to issue commands properly, I am adding sudo in front of all the docker commands such as sudo docker pull wordpress. Anyway, the sudo solved my Cannot connect to daemon problem. However, I needed to install docker into an ubuntu container, in the same way, I did for the host computer. I have researched and found the following solutions, but they didn't work for the container (I ran apt-get update before all these):

1. Use sudo. Didn't work.
2. sudo usermod -aG docker <your username>. Didn't work.
3. sudo usermod -aG docker $USER. Didn't work.

About sudo command, though, it was not available in the container. So I had to run apt-get install sudo. Then, sudo started working but not docker. docker command itself works. But, when you make a request via Docker CLI to docker engine, it says it is not connected, or daemon is not working. Also, the default user in the docker ubuntu container is root. When you enter into the bash TTY, you see root@[some number]. I am using the following command to install docker: sudo apt-get install docker.io. I have followed the instructions here to install docker on my host Linux machine:

1. https://docs.docker.com/engine/installation/linux/ubuntulinux/
2. https://www.digitalocean.com/community/tutorials/how-to-install-and-use-docker-on-ubuntu-16-04

But what really worked was:

https://www.liquidweb.com/kb/how-to-install-docker-on-ubuntu-14-04-lts/

Answer 1

Inside you Ubuntu:xenial container perform the following. [assuming you will be using the root user inside the container]

apt-get update

apt-get install apt-transport-https ca-certificates

apt-key adv \ --keyserver hkp://ha.pool.sks-keyservers.net:80 \ --recv-keys 58118E89F3A912897C070ADBF76221572C52609D

echo "<REPO>" | sudo tee /etc/apt/sources.list.d/docker.list

In place of repo add the deb https://apt.dockerproject.org/repo ubuntu-xenial main

apt-get update

apt-get install linux-image-extra-$(uname -r) linux-image-extra-virtual

apt-get install docker-engine

The above steps should install docker inside your container.

Please refer to this link