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docs: add environment variables configuration method for Docker daemon #25075

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13ea97f
fix: update misleading Image Management description in hub-images index
May 15, 2026
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Merge remote-tracking branch 'upstream/main' into fix/sbx-ubuntu-inst…
May 16, 2026
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docs: add environment variables configuration method for Docker daemon
May 16, 2026
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29 changes: 28 additions & 1 deletion content/manuals/engine/daemon/_index.md
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Expand Up @@ -37,11 +37,12 @@ This page shows you how to customize the Docker daemon, `dockerd`.

## Configure the Docker daemon

There are two ways to configure the Docker daemon:
There are three ways to configure the Docker daemon:

- Use a JSON configuration file. This is the preferred option, since it keeps
all configurations in a single place.
- Use flags when starting `dockerd`.
- Use environment variables to set daemon options.

You can use both of these options together as long as you don't specify the same
option both as a flag and in the JSON file. If that happens, the Docker daemon
Expand Down Expand Up @@ -92,6 +93,32 @@ running:
$ dockerd --help
```

### Configuration using environment variables

You can configure the Docker daemon using environment variables. This is useful
in systemd service overrides or init scripts.

To set environment variables for the Docker daemon using systemd, create a
drop-in override file:
Comment on lines +98 to +102
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@thaJeztah thaJeztah May 21, 2026

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See my other comment; I think this is a very limited use-case, so not 100% sure if we should advertise this here; we could link to the https://docs.docker.com/reference/cli/dockerd/#environment-variables section to make users aware of environment variables that are supported, but possibly leave it an exercise to the user to use those (which is just general systemd knowledge)


````````console
$ sudo systemctl edit docker
```````
Comment on lines +104 to +106

Add the following:

``````ini
[Service]
Environment="DOCKER_OPTS=--debug --tls=true"
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@thaJeztah thaJeztah May 21, 2026

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This is not something we support, the DOCKER_OPTS env-var was a legacy option before systemd;
https://github.com/moby/moby/blob/721883f7329e0c555ec00126ecb3bbe5511d50f5/contrib/init/openrc/docker.confd#L31-L32

some options can also be set through environment variables, but the list is limited;
https://docs.docker.com/reference/cli/dockerd/#environment-variables

So, not entirely sure if we want to advertise this as an alternative to the daemon.json or CLI flags, because it's not a replacement (only for some options).

cc @dvdksn any thoughts?

`````

Then reload and restart the daemon:

````console
$ sudo systemctl daemon-reload
$ sudo systemctl restart docker
```
Comment on lines +96 to +120

## Daemon data directory

The Docker daemon persists all data in a single directory. This tracks
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