Control Docker with systemd
Estimated reading time: 4 minutesMany Linux distributions use systemd to start the Docker daemon. This document shows a few examples of how to customize Docker’s settings.
Start the Docker daemon
Start manually
Once Docker is installed, you need to start the Docker daemon.
Most Linux distributions use systemctl
to start services. If you
do not have systemctl
, use the service
command.
-
systemctl
:$ sudo systemctl start docker
-
service
:$ sudo service docker start
Start automatically at system boot
If you want Docker to start at boot, see Configure Docker to start on boot.
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 the platform-independent
daemon.json
file, which is located in /etc/docker/
on Linux by default. See
Daemon configuration file.
You can configure nearly all daemon configuration options using daemon.json
. The following
example configures two options. One thing you cannot configure using daemon.json
mechanism is
a HTTP proxy.
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.
To accomplish this, set the following flags in the daemon.json
file:
{
"data-root": "/mnt/docker-data",
"storage-driver": "overlay"
}
HTTP/HTTPS proxy
The Docker daemon uses the HTTP_PROXY
, HTTPS_PROXY
, and NO_PROXY
environmental variables in
its start-up environment to configure HTTP or HTTPS proxy behavior. You cannot configure
these environment variables using the daemon.json
file.
This example overrides the default docker.service
file.
If you are behind an HTTP or HTTPS proxy server, for example in corporate settings, you need to add this configuration in the Docker systemd service file.
-
Create a systemd drop-in directory for the docker service:
$ sudo mkdir -p /etc/systemd/system/docker.service.d
-
Create a file called
/etc/systemd/system/docker.service.d/http-proxy.conf
that adds theHTTP_PROXY
environment variable:[Service] Environment="HTTP_PROXY=http://proxy.example.com:80/"
Or, if you are behind an HTTPS proxy server, create a file called
/etc/systemd/system/docker.service.d/https-proxy.conf
that adds theHTTPS_PROXY
environment variable:[Service] Environment="HTTPS_PROXY=https://proxy.example.com:443/"
-
If you have internal Docker registries that you need to contact without proxying you can specify them via the
NO_PROXY
environment variable.The
NO_PROXY
variable specifies a string that contains comma-separated values for hosts that should be excluded from proxying. These are the options you can specify to exclude hosts:- IP address prefix (
1.2.3.4
) - Domain name, or a special DNS label (
*
) - A domain name matches that name and all subdomains. A domain name with
a leading “.” matches subdomains only. For example, given the domains
foo.example.com
andexample.com
:example.com
matchesexample.com
andfoo.example.com
, and.example.com
matches onlyfoo.example.com
- A single asterisk (
*
) indicates that no proxying should be done - Literal port numbers are accepted by IP address prefixes (
1.2.3.4:80
) and domain names (foo.example.com:80
)
Config examples:
[Service] Environment="HTTP_PROXY=http://proxy.example.com:80/" "NO_PROXY=localhost,127.0.0.1,docker-registry.example.com,.corp"
Or, if you are behind an HTTPS proxy server:
[Service] Environment="HTTPS_PROXY=https://proxy.example.com:443/" "NO_PROXY=localhost,127.0.0.1,docker-registry.example.com,.corp"
- IP address prefix (
-
Flush changes:
$ sudo systemctl daemon-reload
-
Restart Docker:
$ sudo systemctl restart docker
-
Verify that the configuration has been loaded:
$ systemctl show --property=Environment docker Environment=HTTP_PROXY=http://proxy.example.com:80/
Or, if you are behind an HTTPS proxy server:
$ systemctl show --property=Environment docker Environment=HTTPS_PROXY=https://proxy.example.com:443/
Configure where the Docker daemon listens for connections
See Configure where the Docker daemon listens for connections.
Manually create the systemd unit files
When installing the binary without a package, you may want
to integrate Docker with systemd. For this, install the two unit files
(service
and socket
) from the github
repository
to /etc/systemd/system
.