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Update systemd.md (#2353) 

Addressing feedback in #1997
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@ -9,147 +9,62 @@ title: Control and configure Docker with systemd
Many Linux distributions use systemd to start the Docker daemon. This document Many Linux distributions use systemd to start the Docker daemon. This document
shows a few examples of how to customize Docker's settings. shows a few examples of how to customize Docker's settings.
## Starting the Docker daemon ## Start the Docker daemon
### Start manually
Once Docker is installed, you will need to start the Docker daemon. Once Docker is installed, you will need to start the Docker daemon.
Most Linux distributions use `systemctl` to start services. If you
do not have `systemctl`, use the `service` command.
```bash - **`systemctl`**:
$ 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: ```bash
$ sudo systemctl start docker
```
```bash - **`service`**:
$ sudo systemctl enable docker
# or on older distributions, you may need to use ```bash
$ sudo chkconfig docker on $ sudo service docker start
``` ```
### Start automatically at system boot
If you want Docker to start at boot, see
[Configure Docker to start on boot](/engine/installation/linux/linux-postinstall.md/#configure-docker-to-start-on-boot).
## Custom Docker daemon options ## Custom Docker daemon options
There are a number of ways to configure the daemon flags and environment variables There are a number of ways to configure the daemon flags and environment variables
for your Docker daemon. 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](/engine/reference/commandline/dockerd.md/#daemon-configuration-file).
The recommended way is to use a systemd drop-in file (as described in the <a You can configure nearly all daemon configuration options using `daemon.json`. The following
target="_blank" example configures two options. One thing you cannot configure using `daemon.json` mechanism is
href="https://www.freedesktop.org/software/systemd/man/systemd.unit.html">systemd.unit</a> a [HTTP proxy](#http-proxy).
documentation). These are local files named `<something>.conf` in the
`/etc/systemd/system/docker.service.d` directory.
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:
```conf
[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 `EnvironmentFile`:
```bash
$ systemctl show docker | grep EnvironmentFile
EnvironmentFile=-/etc/sysconfig/docker (ignore_errors=yes)
```
Alternatively, find out where the service file is located:
```bash
$ 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](systemd.md#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 ### Runtime directory and storage driver
You may want to control the disk space used for Docker images, containers You may want to control the disk space used for Docker images, containers
and volumes by moving it to a separate partition. and volumes by moving it to a separate partition.
In this example, we'll assume that your `docker.service` file looks something To accomplish this, set the following flags in the `daemon.json` file:
like:
```conf ```none
[Unit] {
Description=Docker Application Container Engine "graph": "/mnt/docker-data",
Documentation=https://docs.docker.com "storage-drivers": "overlay"
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 `/etc/systemd/system/docker.service.d`
directory:
```conf
[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:
```conf
[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:
```conf
docker.service has more than one ExecStart= setting, which is only allowed for Type=oneshot services. Refusing.
``` ```
### HTTP proxy ### HTTP proxy
The Docker daemon uses the `HTTP_PROXY` and `NO_PROXY` environmental variables in
its start-up environment to configure HTTP proxy behavior. You cannot configure
these environment variables using the `daemon.json` file.
This example overrides the default `docker.service` file. This example overrides the default `docker.service` file.
If you are behind an HTTP proxy server, for example in corporate settings, If you are behind an HTTP proxy server, for example in corporate settings,
@ -197,7 +112,7 @@ you will need to add this configuration in the Docker systemd service file.
## Manually creating the systemd unit files ## Manually creating the systemd unit files
When installing the binary without a package, you may want When installing the binary without a package, you may want
to integrate Docker with systemd. For this, simply install the two unit files to integrate Docker with systemd. For this, install the two unit files
(service and socket) from [the github (`service` and `socket`) from [the github
repository](https://github.com/docker/docker/tree/master/contrib/init/systemd) repository](https://github.com/docker/docker/tree/master/contrib/init/systemd)
to `/etc/systemd/system`. to `/etc/systemd/system`.