Unable to start docker after configuring hosts in daemon.json

user_3899474 0
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I'm trying to configure docker (version 17.03.1-ce) in ubuntu 16.04 using configuration file /etc/docker/daemon.json to add an host:

{
  "debug": true,
  "hosts": ["tcp://0.0.0.0:1234", "unix:///var/run/docker.sock"],
  "dns"  : ["8.8.8.8","8.8.4.4"]
}

when I try to restart docker.. it fails

#service docker restart
Job for docker.service failed because the control process exited with error code. See "systemctl status docker.service" and "journalctl -xe" for details.

watching on systemctl status docker.service:

Starting Docker Application Container Engine...
docker-slave-ubuntu-build dockerd[24806]: unable to configure the Docker daemon with file /etc/docker/daemon.json: 
the following directives are specified both as a flag and in the configuration file: 
hosts: (from flag: [fd://], from file: [tcp://0.0.0.0:4243 unix:///var/run/docker.sock])

Where I can remove the mentioned flag ? I have to modify maintainer's script ?

ubuntu-16.04 docker service configuration
5 Answers

I found this on the Docker docs and it worked on Docker 18.09.1 and Centos 8:

To work around this problem, create a new file /etc/systemd/system/docker.service.d/docker.conf with the following contents, to remove the -H argument that is used when starting the daemon by default.

[Service]
ExecStart=
ExecStart=/usr/bin/dockerd

Then reload

systemctl daemon-reload

The reason is:

Docker listens on a socket by default. On Debian and Ubuntu systems using systemd, this means that a host flag -H is always used when starting dockerd. If you specify a hosts entry in the daemon.json, this causes a configuration conflict (as in the above message) and Docker fails to start.

Here is the link: https://docs.docker.com/config/daemon/#troubleshoot-conflicts-between-the-daemonjson-and-startup-scripts

user_142566220

In my case I tried to add both the daemon.json under /etc/docker and a *.conf file under /etc/systemd/system/docker.service.d. It turned out it was enough to have a .conf file only (in my case called override.conf):

[Service]
ExecStart=
ExecStart=/usr/bin/dockerd -H tcp://0.0.0.0:2375

this way I could expose the docker socket.

user_20394550

I had copied the daemon.json from a website. After running 

sudo systemctl stop docker
/usr/sbin/dockerd

it showed me a better error message that stated that I had a strange invisible character in the daemon.json file

user_113047250
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