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page_title: Controlling and configuring Docker using Systemd page_description: Controlling and configuring Docker using Systemd page_keywords: docker, daemon, systemd, configuration

Controlling and configuring Docker using 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.

Or, you may need to edit the docker.service file, which can be in /usr/lib/systemd/system or /etc/systemd/service.

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=http://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 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

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.

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