Docker apt-get update fails

问题:

Can somebody help me get apt-get working in my docker container? Whenever I try running any apt-get command in my docker container, the command fails. I'm running Docker version 1.1.1, build bd609d2 on ubuntu 12.04.

When I do

$ sudo docker run -i -t ubuntu:14.04 /bin/bash
# apt-get update

I get errors saying

Could not resolve 'archive.ubuntu.com'

I tried uncommenting the line below in /etc/default/docker

DOCKER_OPTS="--dns 8.8.8.8 --dns 8.8.4.4"

but I still can't ping google.com

ping: unknown host

I confirmed that the container is using the dns servers 8.8.8.8 and 8.8.4.4

root@0baa87fc6322:/# cat /etc/resolv.conf

nameserver 8.8.8.8

nameserver 8.8.4.4

and I'm able to ping both servers so I'm pretty sure that a firewall isn't just dropping my packets.

Any help with this would be appreciated!

Thanks!

回答1:

Thanks for all your help! I found out it was a dns problem and that it was because of a firewall. After searching some more I found this question that I wasn't able to find while searching 'docker apt-get fail'

Docker - Network calls fail during image build on corporate network

His problem was similar to mine and the solution helped me get it working. I've copied over his solution for anybody that finds this question in the future.

Those Google servers weren't accessible from behind our firewall, which is why we couldn't resolve any URLs.

The fix is to tell Docker which DNS servers to use. This fix depends on how you installed Docker: Ubuntu Package

If you have the Ubuntu package installed, edit /etc/default/docker and add the following line:

DOCKER_OPTS="--dns <your_dns_server_1> --dns <your_dns_server_2>"

You can add as many DNS servers as you want to this config. Once you've edited this file you'll want to restart your Docker service:

sudo service docker restart

Binaries

If you've installed Docker via the binaries method (i.e. no package), then you set the DNS servers when you start the Docker daemon:

sudo docker -d -D --dns --dns &

回答2:

If you see an error like Could not resolve ..., it is likely a DNS configuration.

First thing to check is run cat /etc/resolv.conf in the docker container. If it has an invalid DNS server, such as nameserver 127.0.x.x, then the container will not be able to resolve the domain names into ip addresses, so ping google.com will fail.

Second thing to check is run cat /etc/resolv.conf on the host machine. Docker basically copies the host's /etc/resolv.conf to the container everytime a container is started. So if the host's /etc/resolv.conf is wrong, then so will the docker container.

If you have found that the host's /etc/resolv.conf is wrong, then you have 2 options:

1. Hardcode the DNS server in daemon.json. This is easy, but not ideal if you expect the DNS server to change.

2. Fix the hosts's /etc/resolv.conf. This is a little trickier, but it is generated dynamically, and you are not hardcoding the DNS server.

---

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.

回答3:

First check if you have connection, ping directly to ip 91.189.92.201 that archive.ubuntu.com is pointed to:

ping 91.189.92.201

If you still can't reach the host it's not a dns problem.

Also if you have internet connection, you can make a hack. Just put a row into /etc/hosts file and problem solved:

91.189.92.201 archive.ubuntu.com

回答4:

I encounter the issue in two different case and the resolution was different...

First one with Win7 + virtualbox(Xubuntu 16.04) This comment did the job:https://stackoverflow.com/a/29659783/2260796

I modify the file /etc/default/docker:

DOCKER-OPTS="--ip-masq=true --dns my_ip_dns_win --dns 8.8.8.8 --dns 8.8.4.4" And run sudo service docker restart

Second one on a Xubuntu OS (ubuntu 16.04) The precedent resolution was not enough. This comment did the job: https://github.com/docker/docker/issues/1809 I had to comment one line in file /etc/NetworkManager/NetworkManager.conf:

dns=dnsmasq

Then run

sudo restart network-manager

回答5:

I am using the version of Mint and after installing Docker and try to create an image of Ubuntu to do the apt-get update command does not recognize, to remedy the problem, I did step down

docker run -it -p 8080:80  ubuntu /bin/bash
echo "91.189.92.201 archive.ubuntu.com" >> /etc/hosts
cat /etc/hosts
apt-get update

回答6:

I faced the same problem with docker-compose. I solve that by adding ENV http_proxy 'proxy.com' entry into Dockerfile.