moby--moby/docs/articles/systemd.md

Control and configure Docker with systemd

Many Linux distributions use systemd to start the Docker daemon. This document shows a few examples of how to customise Docker's settings.

Starting the Docker daemon

Once Docker is installed, you will need to start the Docker daemon.

$ sudo systemctl start docker
# or on older distributions, you may need to use
$ sudo service docker start

If you want Docker to start at boot, you should also:

$ sudo systemctl enable docker
# or on older distributions, you may need to use
$ sudo chkconfig docker on

Custom Docker daemon options

There are a number of ways to configure the daemon flags and environment variables for your Docker daemon.

If the docker.service file is set to use an EnvironmentFile (often pointing to /etc/sysconfig/docker) then you can modify the referenced file.

Check if the docker.service uses an EnvironmentFile:

$ sudo systemctl show docker | grep EnvironmentFile
EnvironmentFile=-/etc/sysconfig/docker (ignore_errors=yes)

Alternatively, find out where the service file is located, and look for the property:

$ sudo systemctl status docker | grep Loaded
   Loaded: loaded (/usr/lib/systemd/system/docker.service; enabled)
$ sudo grep EnvironmentFile /usr/lib/systemd/system/docker.service
EnvironmentFile=-/etc/sysconfig/docker

You can customize the Docker daemon options using override files as explained in the HTTP Proxy example below. The files located in /usr/lib/systemd/system or /lib/systemd/system contain the default options and should not be edited.

Runtime directory and storage driver

You may want to control the disk space used for Docker images, containers and volumes by moving it to a separate partition.

In this example, we'll assume that your docker.service file looks something like:

[Unit]
Description=Docker Application Container Engine
Documentation=https://docs.docker.com
After=network.target docker.socket
Requires=docker.socket

[Service]
Type=notify
EnvironmentFile=-/etc/sysconfig/docker
ExecStart=/usr/bin/docker -d -H fd:// $OPTIONS
LimitNOFILE=1048576
LimitNPROC=1048576

[Install]
Also=docker.socket

This will allow us to add extra flags to the /etc/sysconfig/docker file by setting OPTIONS:

OPTIONS="--graph /mnt/docker-data --storage-driver btrfs"

You can also set other environment variables in this file, for example, the HTTP_PROXY environment variables described below.

HTTP proxy

This example overrides the default docker.service file.

If you are behind a HTTP proxy server, for example in corporate settings, you will need to add this configuration in the Docker systemd service file.

First, create a systemd drop-in directory for the docker service:

mkdir /etc/systemd/system/docker.service.d

Now create a file called /etc/systemd/system/docker.service.d/http-proxy.conf that adds the HTTP_PROXY environment variable:

[Service]
Environment="HTTP_PROXY=http://proxy.example.com:80/"

If you have internal Docker registries that you need to contact without proxying you can specify them via the NO_PROXY environment variable:

Environment="HTTP_PROXY=http://proxy.example.com:80/" "NO_PROXY=localhost,127.0.0.0/8,docker-registry.somecorporation.com"

Flush changes:

$ sudo systemctl daemon-reload

Verify that the configuration has been loaded:

$ sudo systemctl show docker --property Environment
Environment=HTTP_PROXY=http://proxy.example.com:80/

Restart Docker:

$ sudo systemctl restart docker

Manually creating the systemd unit files

When installing the binary without a package, you may want to integrate Docker with systemd. For this, simply install the two unit files (service and socket) from the github repository to /etc/systemd/system.