Control and configure Docker with systemdEstimated reading time: 5 minutes
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 systemd.unit
documentation). These are local files named
<something>.conf in the
However, if you had previously used a package which had an
(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/dockerd $OPTIONS \ $DOCKER_STORAGE_OPTIONS \ $DOCKER_NETWORK_OPTIONS \ $BLOCK_REGISTRY \ $INSECURE_REGISTRY
To check if the
docker.service uses an
$ 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 below. The files located in
/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
[Unit] Description=Docker Application Container Engine Documentation=https://docs.docker.com After=network.target [Service] Type=notify # the default is not to use systemd for cgroups because the delegate issues still # exists and systemd currently does not support the cgroup feature set required # for containers run by docker ExecStart=/usr/bin/dockerd ExecReload=/bin/kill -s HUP $MAINPID # Having non-zero Limit*s causes performance problems due to accounting overhead # in the kernel. We recommend using cgroups to do container-local accounting. LimitNOFILE=infinity LimitNPROC=infinity LimitCORE=infinity # Uncomment TasksMax if your systemd version supports it. # Only systemd 226 and above support this version. #TasksMax=infinity TimeoutStartSec=0 # set delegate yes so that systemd does not reset the cgroups of docker containers Delegate=yes # kill only the docker process, not all processes in the cgroup KillMode=process [Install] WantedBy=multi-user.target
This will allow us to add extra flags via a drop-in file (mentioned above) by
placing a file containing the following in the
[Service] ExecStart= ExecStart=/usr/bin/dockerd --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/dockerd --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.
This example overrides the default
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.
Create a systemd drop-in directory for the docker service:
$ mkdir -p /etc/systemd/system/docker.service.d
Create a file called
/etc/systemd/system/docker.service.d/http-proxy.confthat adds the
If you have internal Docker registries that you need to contact without proxying you can specify them via the
$ sudo systemctl daemon-reload
Verify that the configuration has been loaded:
$ systemctl show --property=Environment docker Environment=HTTP_PROXY=http://proxy.example.com:80/
$ 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