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<!--[metadata]>
+++
aliases = ["/engine/articles/systemd/"]
title = "Control and configure Docker with systemd"
description = "Controlling and configuring Docker using systemd"
keywords = ["docker, daemon, systemd, configuration"]
[menu.main]
parent = "engine_admin"
+++
<![end-metadata]-->
# 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 customize 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.
The recommended way is to use a systemd drop-in file (as described in
the <a target="_blank"
href="https://www.freedesktop.org/software/systemd/man/systemd.unit.html">systemd.unit</a>
documentation). These are local files named `<something>.conf` in the
`/etc/systemd/system/docker.service.d` directory. This could also be
`/etc/systemd/system/docker.service`, which also works for overriding
the defaults from `/lib/systemd/system/docker.service`.
However, if you had previously used a package which had an
`EnvironmentFile` (often pointing to `/etc/sysconfig/docker`) then for
backwards compatibility, you drop a file with a `.conf` extension into
the `/etc/systemd/system/docker.service.d` directory including the
following:
[Service]
EnvironmentFile=-/etc/sysconfig/docker
EnvironmentFile=-/etc/sysconfig/docker-storage
EnvironmentFile=-/etc/sysconfig/docker-network
ExecStart=
ExecStart=/usr/bin/docker daemon -H fd:// $OPTIONS \
$DOCKER_STORAGE_OPTIONS \
$DOCKER_NETWORK_OPTIONS \
$BLOCK_REGISTRY \
$INSECURE_REGISTRY
To check if the `docker.service` uses an `EnvironmentFile`:
$ systemctl show docker | grep EnvironmentFile
EnvironmentFile=-/etc/sysconfig/docker (ignore_errors=yes)
Alternatively, find out where the service file is located:
$ systemctl show --property=FragmentPath docker
FragmentPath=/usr/lib/systemd/system/docker.service
$ 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](#http-proxy) 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
ExecStart=/usr/bin/docker daemon -H fd://
LimitNOFILE=1048576
LimitNPROC=1048576
TasksMax=1048576
[Install]
Also=docker.socket
This will allow us to add extra flags via a drop-in file (mentioned above) by
placing a file containing the following in the `/etc/systemd/system/docker.service.d`
directory:
[Service]
ExecStart=
ExecStart=/usr/bin/docker daemon -H fd:// --graph="/mnt/docker-data" --storage-driver=overlay
You can also set other environment variables in this file, for example, the
`HTTP_PROXY` environment variables described below.
To modify the ExecStart configuration, specify an empty configuration followed
by a new configuration as follows:
[Service]
ExecStart=
ExecStart=/usr/bin/docker daemon -H fd:// --bip=172.17.42.1/16
If you fail to specify an empty configuration, Docker reports an error such as:
docker.service has more than one ExecStart= setting, which is only allowed for Type=oneshot services. Refusing.
### HTTP proxy
This example overrides the default `docker.service` file.
If you are behind an 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,127.0.0.1,docker-registry.somecorporation.com"
Flush changes:
$ sudo systemctl daemon-reload
Verify that the configuration has been loaded:
$ systemctl show --property=Environment docker
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](https://github.com/docker/docker/tree/master/contrib/init/systemd)
to `/etc/systemd/system`.
|
