I had same issue while setting up dockers for first time ever and
tried on two Ubuntu Server (16.04.3 Xenial) VM’s in home network with same problem with pulling HELLO-WORLD image after fresh installing
and after few days for digging in much promised post for setting proxy in home NETWORK and none of these works
setting proxying in home network where no proxy has been setup 
, linux or windows or mac, proxy is same accross everywhere like internet…
#curl https://registry-1.docker.io/v2/ to see can get respose and setup credentials…
ubuntu@ubuntuserver:~$ docker pull hello-world
Using default tag: latest
Error response from daemon: Get https://registry-1.docker.io/v2/: net/http: request canceled while waiting for connection (Client.Timeout exceeded while awaiting headers)
ubuntu@ubuntuserver:~$ cat /etc/systemd/system/docker.service.d/http-proxy.conf
cat: /etc/systemd/system/docker.service.d/http-proxy.conf: No such file or directory
ubuntu@ubuntuserver:~$ sudo nano /etc/resolv.conf
#add these lines on top and above one for home router…
nameserver 8.8.8.8
nameserver 8.8.4.4
ubuntu@ubuntuserver:~$ sudo systemctl daemon-reload #THIS IS RESCUE COMMAND…
ubuntu@ubuntuserver:~$ sudo systemctl restart docker
ubuntu@ubuntuserver:~$ sudo systemctl status docker
ubuntu@ubuntuserver:~$ docker pull hello-world
Using default tag: latest
latest: Pulling from library/hello-world
5b0f327be733: Pull complete
Digest: sha256:07d5f7800dfe37b8c2196c7b1c524c33808ce2e0f74e7aa00e603295ca9a0972
Status: Downloaded newer image for hello-world:latest
ubuntu@ubuntuserver:~$ docker run hello-world
Hello from Docker!
This message shows that your installation appears to be working correctly.
…