Docker_Ubuntu-18.04

**1\. Hardcode DNS server in docker daemon.json**

*   Edit `/etc/docker/daemon.json`

        {
            "dns": ["10.1.2.3", "8.8.8.8"]
        }

*   Restart the docker daemon for those changes to take effect:  
     `sudo systemctl restart docker`

*   Now when you run/start a container, docker will populate `/etc/resolv.conf` with the values from `daemon.json`.

* * *

**2\. Fix the hosts's `/etc/resolv.conf`**

**A. Ubuntu 16.04 and earlier**

*   For Ubuntu 16.04 and earlier, `/etc/resolv.conf` was dynamically generated by NetworkManager.

*   Comment out the line `dns=dnsmasq` (with a `#`) in `/etc/NetworkManager/NetworkManager.conf`

*   Restart the NetworkManager to regenerate `/etc/resolv.conf` :  
     `sudo systemctl restart network-manager`

*   Verify on the host: `cat /etc/resolv.conf`

**B. Ubuntu 18.04 and later**

*   Ubuntu 18.04 changed to use [`systemd-resolved` to generate `/etc/resolv.conf`](http://manpages.ubuntu.com/manpages/bionic/man8/systemd-resolved.service.8.html#contenttoc3). Now by default it uses a local DNS cache 127.0.0.53\. That will not work inside a container, so Docker will default to Google's 8.8.8.8 DNS server, which may break for people behind a firewall.

*   `/etc/resolv.conf` is actually a symlink (`ls -l /etc/resolv.conf`) which points to `/run/systemd/resolve/stub-resolv.conf` (127.0.0.53) by default in Ubuntu 18.04.

*   Just change the symlink to point to `/run/systemd/resolve/resolv.conf`, which lists the real DNS servers:  
     `sudo ln -sf /run/systemd/resolve/resolv.conf /etc/resolv.conf`

*   Verify on the host: `cat /etc/resolv.conf`

Now you should have a valid `/etc/resolv.conf` on the host for docker to copy into the containers.

## Install Docker



'

sudo apt-get install bridge-utils
sudo pkill docker
sudo iptables -t nat -F
sudo ifconfig docker0 down
sudo brctl delbr docker0
sudo service docker restart

'

1. Hardcode DNS server in docker daemon.json

• Edit /etc/docker/daemon.json

  {
      "dns": ["10.1.2.3", "8.8.8.8"]
  }
  

• Restart the docker daemon for those changes to take effect:
  sudo systemctl restart docker

• Now when you run/start a container, docker will populate /etc/resolv.conf with the values from daemon.json.

---

2. Fix the hosts's /etc/resolv.conf

A. Ubuntu 16.04 and earlier

• For Ubuntu 16.04 and earlier, /etc/resolv.conf was dynamically generated by NetworkManager.

• Comment out the line dns=dnsmasq (with a #) in /etc/NetworkManager/NetworkManager.conf

• Restart the NetworkManager to regenerate /etc/resolv.conf :
  sudo systemctl restart network-manager

• Verify on the host: cat /etc/resolv.conf

B. Ubuntu 18.04 and later

• Ubuntu 18.04 changed to use systemd-resolved to generate /etc/resolv.conf. Now by default it uses a local DNS cache 127.0.0.53. That will not work inside a container, so Docker will default to Google's 8.8.8.8 DNS server, which may break for people behind a firewall.

• /etc/resolv.conf is actually a symlink (ls -l /etc/resolv.conf) which points to /run/systemd/resolve/stub-resolv.conf (127.0.0.53) by default in Ubuntu 18.04.

• Just change the symlink to point to /run/systemd/resolve/resolv.conf, which lists the real DNS servers:
  sudo ln -sf /run/systemd/resolve/resolv.conf /etc/resolv.conf

• Verify on the host: cat /etc/resolv.conf

Now you should have a valid /etc/resolv.conf on the host for docker to copy into the containers.

Install Docker

https://docs.docker.com/install/linux/docker-ce/ubuntu/

sudo apt-get update
sudo apt-get install \
apt-transport-https \
ca-certificates \
curl \
gnupg-agent \
software-properties-common -y

curl -fsSL https://download.docker.com/linux/ubuntu/gpg | sudo apt-key add -
sudo apt-key fingerprint 0EBFCD88
sudo add-apt-repository \
"deb [arch=amd64] https://download.docker.com/linux/ubuntu \
$(lsb_release -cs) \
stable"

sudo apt-get update
sudo apt-get install docker-ce docker-ce-cli containerd.io -y
sudo docker run hello-world

Manage Docker as a non-root user

• Create the docker group.

   sudo groupadd docker
  

• Add your user to the docker group.

  sudo usermod -aG docker $USER
  

• Log out and log back in so that your group membership is re-evaluated.

  If testing on a virtual machine, it may be necessary to restart the virtual machine for changes to take effect.

  On a desktop Linux environment such as X Windows, log out of your session completely and then log back in.

• Verify that you can run docker commands without sudo.

  $ docker run hello-world
  

  This command download

Docker containers can't resolve DNS on Ubuntu 14.04 Desktop Host

Woo, I found a post on github that solved my problem.

After Steve K. pointed out that it wasn't actually a DNS issue and was a connectivity issue, I was able to find a post on github that described how to fix this problem.

Apparently the docker0 network bridge was hung up. Installing bridge-utils and running the following got my Docker in working order:

sudo apt-get install bridge-utils -y
sudo pkill docker
sudo iptables -t nat -F
sudo ifconfig docker0 down
sudo brctl delbr docker0
sudo service docker restart

docker-library/busybox#48