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