DockerCLI/docs/reference/commandline/dockerd.md

---
title: "dockerd"
description: "The daemon command description and usage"
keywords: "container, daemon, runtime"
redirect_from:
- /engine/reference/commandline/daemon/
---

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# daemon

```markdown
Usage: dockerd [OPTIONS]

A self-sufficient runtime for containers.

Options:
      --add-runtime runtime                   Register an additional OCI compatible runtime (default [])
      --allow-nondistributable-artifacts list Allow push of nondistributable artifacts to registry
      --api-cors-header string                Set CORS headers in the Engine API
      --authorization-plugin list             Authorization plugins to load
      --bip string                            Specify network bridge IP
  -b, --bridge string                         Attach containers to a network bridge
      --cgroup-parent string                  Set parent cgroup for all containers
      --config-file string                    Daemon configuration file (default "/etc/docker/daemon.json")
      --containerd string                     containerd grpc address
      --containerd-namespace string           Containerd namespace to use (default "moby")
      --containerd-plugins-namespace string   Containerd namespace to use for plugins (default "plugins.moby")
      --cpu-rt-period int                     Limit the CPU real-time period in microseconds for the
                                              parent cgroup for all containers (not supported with cgroups v2)
      --cpu-rt-runtime int                    Limit the CPU real-time runtime in microseconds for the
                                              parent cgroup for all containers (not supported with cgroups v2)
      --cri-containerd                        start containerd with cri
      --data-root string                      Root directory of persistent Docker state (default "/var/lib/docker")
  -D, --debug                                 Enable debug mode
      --default-address-pool pool-options     Default address pools for node specific local networks
      --default-cgroupns-mode string          Default mode for containers cgroup namespace ("host" | "private") (default "private")
      --default-gateway ip                    Container default gateway IPv4 address
      --default-gateway-v6 ip                 Container default gateway IPv6 address
      --default-ipc-mode string               Default mode for containers ipc ("shareable" | "private") (default "private")
      --default-runtime string                Default OCI runtime for containers (default "runc")
      --default-shm-size bytes                Default shm size for containers (default 64MiB)
      --default-ulimit ulimit                 Default ulimits for containers (default [])
      --dns list                              DNS server to use
      --dns-opt list                          DNS options to use
      --dns-search list                       DNS search domains to use
      --exec-opt list                         Runtime execution options
      --exec-root string                      Root directory for execution state files (default "/var/run/docker")
      --experimental                          Enable experimental features
      --fixed-cidr string                     IPv4 subnet for fixed IPs
      --fixed-cidr-v6 string                  IPv6 subnet for fixed IPs
  -G, --group string                          Group for the unix socket (default "docker")
      --help                                  Print usage
  -H, --host list                             Daemon socket(s) to connect to
      --host-gateway-ip ip                    IP address that the special 'host-gateway' string in --add-host resolves to.
                                              Defaults to the IP address of the default bridge
      --http-proxy string                     HTTP proxy URL to use for outgoing traffic
      --https-proxy string                    HTTPS proxy URL to use for outgoing traffic
      --icc                                   Enable inter-container communication (default true)
      --init                                  Run an init in the container to forward signals and reap processes
      --init-path string                      Path to the docker-init binary
      --insecure-registry list                Enable insecure registry communication
      --ip ip                                 Default IP when binding container ports (default 0.0.0.0)
      --ip-forward                            Enable net.ipv4.ip_forward (default true)
      --ip-masq                               Enable IP masquerading (default true)
      --ip6tables                             Enable addition of ip6tables rules (experimental)
      --iptables                              Enable addition of iptables rules (default true)
      --ipv6                                  Enable IPv6 networking
      --label list                            Set key=value labels to the daemon
      --live-restore                          Enable live restore of docker when containers are still running
      --log-driver string                     Default driver for container logs (default "json-file")
  -l, --log-level string                      Set the logging level ("debug"|"info"|"warn"|"error"|"fatal") (default "info")
      --log-opt map                           Default log driver options for containers (default map[])
      --max-concurrent-downloads int          Set the max concurrent downloads (default 3)
      --max-concurrent-uploads int            Set the max concurrent uploads (default 5)
      --max-download-attempts int             Set the max download attempts for each pull (default 5)
      --metrics-addr string                   Set default address and port to serve the metrics api on
      --mtu int                               Set the containers network MTU (default 1500)
      --network-control-plane-mtu int         Network Control plane MTU (default 1500)
      --no-new-privileges                     Set no-new-privileges by default for new containers
      --no-proxy string                       Comma-separated list of hosts or IP addresses for which the proxy is skipped
      --node-generic-resource list            Advertise user-defined resource
      --oom-score-adjust int                  Set the oom_score_adj for the daemon
  -p, --pidfile string                        Path to use for daemon PID file (default "/var/run/docker.pid")
      --raw-logs                              Full timestamps without ANSI coloring
      --registry-mirror list                  Preferred registry mirror
      --rootless                              Enable rootless mode; typically used with RootlessKit
      --seccomp-profile string                Path to seccomp profile. Use "unconfined" to disable the default seccomp profile (default "builtin")
      --selinux-enabled                       Enable selinux support
      --shutdown-timeout int                  Set the default shutdown timeout (default 15)
  -s, --storage-driver string                 Storage driver to use
      --storage-opt list                      Storage driver options
      --swarm-default-advertise-addr string   Set default address or interface for swarm advertised address
      --tls                                   Use TLS; implied by --tlsverify
      --tlscacert string                      Trust certs signed only by this CA (default "~/.docker/ca.pem")
      --tlscert string                        Path to TLS certificate file (default "~/.docker/cert.pem")
      --tlskey string                         Path to TLS key file (default "~/.docker/key.pem")
      --tlsverify                             Use TLS and verify the remote
      --userland-proxy                        Use userland proxy for loopback traffic (default true)
      --userland-proxy-path string            Path to the userland proxy binary
      --userns-remap string                   User/Group setting for user namespaces
      --validate                              Validate daemon configuration and exit
  -v, --version                               Print version information and quit
```

Options with [] may be specified multiple times.

## Description

`dockerd` is the persistent process that manages containers. Docker
uses different binaries for the daemon and client. To run the daemon you
type `dockerd`.

To run the daemon with debug output, use `dockerd --debug` or add `"debug": true`
to [the `daemon.json` file](#daemon-configuration-file).

> **Enabling experimental features**
> 
> Enable experimental features by starting `dockerd` with the `--experimental`
> flag or adding `"experimental": true` to the `daemon.json` file.

### Environment variables

For easy reference, the following list of environment variables are supported
by the `dockerd` command line:

| Variable            | Description                                                                                                                                                                       |
|:--------------------|:----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| `DOCKER_CERT_PATH`  | Location of your authentication keys. This variable is used both by the [`docker` CLI](cli.md) and the `dockerd` daemon.                                                          |
| `DOCKER_DRIVER`     | The storage driver to use.                                                                                                                                                        |
| `DOCKER_RAMDISK`    | If set this disables 'pivot_root'.                                                                                                                                                |
| `DOCKER_TLS_VERIFY` | When set Docker uses TLS and verifies the remote. This variable is used both by the  [`docker` CLI](cli.md) and the `dockerd` daemon.                                             |
| `DOCKER_TMPDIR`     | Location for temporary files created by the daemon.                                                                                                                               |
| `HTTP_PROXY`        | Proxy URL for HTTP requests unless overridden by NoProxy. See the [Go specification](https://pkg.go.dev/golang.org/x/net/http/httpproxy#Config) for details.                      |
| `HTTPS_PROXY`       | Proxy URL for HTTPS requests unless overridden by NoProxy. See the [Go specification](https://pkg.go.dev/golang.org/x/net/http/httpproxy#Config) for details.                     |
| `MOBY_DISABLE_PIGZ` | Disables the use of [`unpigz`](https://linux.die.net/man/1/pigz) to  decompress layers in parallel when pulling images, even if it is installed.                                  |                                                                                                                                                               |
| `NO_PROXY`          | Comma-separated values specifying hosts that should be excluded from proxying. See the [Go specification](https://pkg.go.dev/golang.org/x/net/http/httpproxy#Config) for details. |

## Examples

### Proxy configuration

> **Note**
> 
> Refer to the [Docker Desktop manual](https://docs.docker.com/desktop/networking/#httphttps-proxy-support)
> if you are running [Docker Desktop](https://docs.docker.com/desktop/).

If you are behind an HTTP proxy server, for example in corporate settings,
you may have to configure the Docker daemon to use the proxy server for
operations such as pulling and pushing images. The daemon can be configured
in three ways:

1. Using environment variables (`HTTP_PROXY`, `HTTPS_PROXY`, and `NO_PROXY`).
2. Using the "http-proxy", "https-proxy", and "no-proxy" fields in the
  [daemon configuration file](#daemon-configuration-file) (Docker Engine 23.0 or newer).
3. Using the `--http-proxy`, `--https-proxy`, and `--no-proxy` command-line
  options. (Docker Engine 23.0 or newer).

The command-line and configuration file options take precedence over environment
variables. Refer to [control and configure Docker with systemd](https://docs.docker.com/config/daemon/systemd/#httphttps-proxy)
to set these environment variables on a host using `systemd`.

### Daemon socket option

The Docker daemon can listen for [Docker Engine API](https://docs.docker.com/engine/api/)
requests via three different types of Socket: `unix`, `tcp`, and `fd`.

By default, a `unix` domain socket (or IPC socket) is created at
`/var/run/docker.sock`, requiring either `root` permission, or `docker` group
membership.

If you need to access the Docker daemon remotely, you need to enable the `tcp`
Socket. Beware that the default setup provides un-encrypted and
un-authenticated direct access to the Docker daemon - and should be secured
either using the [built in HTTPS encrypted socket](https://docs.docker.com/engine/security/https/), or by
putting a secure web proxy in front of it. You can listen on port `2375` on all
network interfaces with `-H tcp://0.0.0.0:2375`, or on a particular network
interface using its IP address: `-H tcp://192.168.59.103:2375`. It is
conventional to use port `2375` for un-encrypted, and port `2376` for encrypted
communication with the daemon.

> **Note**
>
> If you're using an HTTPS encrypted socket, keep in mind that only
> TLS1.0 and greater are supported. Protocols SSLv3 and under are not
> supported anymore for security reasons.

On Systemd based systems, you can communicate with the daemon via
[Systemd socket activation](https://0pointer.de/blog/projects/socket-activation.html),
use `dockerd -H fd://`. Using `fd://` will work perfectly for most setups but
you can also specify individual sockets: `dockerd -H fd://3`. If the
specified socket activated files aren't found, then Docker will exit. You can
find examples of using Systemd socket activation with Docker and Systemd in the
[Docker source tree](https://github.com/docker/docker/tree/master/contrib/init/systemd/).

You can configure the Docker daemon to listen to multiple sockets at the same
time using multiple `-H` options:

The example below runs the daemon listenin on the default unix socket, and
on 2 specific IP addresses on this host:

```console
$ sudo dockerd -H unix:///var/run/docker.sock -H tcp://192.168.59.106 -H tcp://10.10.10.2
```

The Docker client will honor the `DOCKER_HOST` environment variable to set the
`-H` flag for the client. Use **one** of the following commands:

```console
$ docker -H tcp://0.0.0.0:2375 ps
```

```console
$ export DOCKER_HOST="tcp://0.0.0.0:2375"

$ docker ps
```

Setting the `DOCKER_TLS_VERIFY` environment variable to any value other than
the empty string is equivalent to setting the `--tlsverify` flag. The following
are equivalent:

```console
$ docker --tlsverify ps
# or
$ export DOCKER_TLS_VERIFY=1
$ docker ps
```

The Docker client will honor the `HTTP_PROXY`, `HTTPS_PROXY`, and `NO_PROXY`
environment variables (or the lowercase versions thereof). `HTTPS_PROXY` takes
precedence over `HTTP_PROXY`.

The Docker client supports connecting to a remote daemon via SSH:

```console
$ docker -H ssh://me@example.com:22/var/run/docker.sock ps
$ docker -H ssh://me@example.com:22 ps
$ docker -H ssh://me@example.com ps
$ docker -H ssh://example.com ps
```

To use SSH connection, you need to set up `ssh` so that it can reach the
remote host with public key authentication. Password authentication is not
supported. If your key is protected with passphrase, you need to set up
`ssh-agent`.

#### Bind Docker to another host/port or a Unix socket

> **Warning**
>
> Changing the default `docker` daemon binding to a
> TCP port or Unix *docker* user group will increase your security risks
> by allowing non-root users to gain *root* access on the host. Make sure
> you control access to `docker`. If you are binding
> to a TCP port, anyone with access to that port has full Docker access;
> so it is not advisable on an open network.
{: .warning :}

With `-H` it is possible to make the Docker daemon to listen on a
specific IP and port. By default, it will listen on
`unix:///var/run/docker.sock` to allow only local connections by the
*root* user. You *could* set it to `0.0.0.0:2375` or a specific host IP
to give access to everybody, but that is **not recommended** because
then it is trivial for someone to gain root access to the host where the
daemon is running.

Similarly, the Docker client can use `-H` to connect to a custom port.
The Docker client will default to connecting to `unix:///var/run/docker.sock`
on Linux, and `tcp://127.0.0.1:2376` on Windows.

`-H` accepts host and port assignment in the following format:

    tcp://[host]:[port][path] or unix://path

For example:

-   `tcp://` -> TCP connection to `127.0.0.1` on either port `2376` when TLS encryption
    is on, or port `2375` when communication is in plain text.
-   `tcp://host:2375` -> TCP connection on
    host:2375
-   `tcp://host:2375/path` -> TCP connection on
    host:2375 and prepend path to all requests
-   `unix://path/to/socket` -> Unix socket located
    at `path/to/socket`

`-H`, when empty, will default to the same value as
when no `-H` was passed in.

`-H` also accepts short form for TCP bindings: `host:` or `host:port` or `:port`

Run Docker in daemon mode:

```console
$ sudo <path to>/dockerd -H 0.0.0.0:5555 &
```

Download an `ubuntu` image:

```console
$ docker -H :5555 pull ubuntu
```

You can use multiple `-H`, for example, if you want to listen on both
TCP and a Unix socket

```console
$ sudo dockerd -H tcp://127.0.0.1:2375 -H unix:///var/run/docker.sock &
# Download an ubuntu image, use default Unix socket
$ docker pull ubuntu
# OR use the TCP port
$ docker -H tcp://127.0.0.1:2375 pull ubuntu
```

### Daemon storage-driver

On Linux, the Docker daemon has support for several different image layer storage
drivers: `overlay2`, `fuse-overlayfs`, `btrfs`, and `zfs`.

`overlay2` is the preferred storage driver for all currently supported Linux distributions,
and is selected by default. Unless users have a strong reason to prefer another storage driver,
`overlay2` should be used.

You can find out more about storage drivers and how to select one in [Select a storage driver](https://docs.docker.com/storage/storagedriver/select-storage-driver/).

On Windows, the Docker daemon only supports the `windowsfilter` storage driver.

### Options per storage driver

Particular storage-driver can be configured with options specified with
`--storage-opt` flags. Options for `zfs` start with `zfs`, and options for
`btrfs` start with `btrfs`.

#### ZFS options

##### `zfs.fsname`

Set zfs filesystem under which docker will create its own datasets.
By default docker will pick up the zfs filesystem where docker graph
(`/var/lib/docker`) is located.

###### Example

```console
$ sudo dockerd -s zfs --storage-opt zfs.fsname=zroot/docker
```

#### Btrfs options

##### `btrfs.min_space`

Specifies the minimum size to use when creating the subvolume which is used
for containers. If user uses disk quota for btrfs when creating or running
a container with **--storage-opt size** option, docker should ensure the
**size** cannot be smaller than **btrfs.min_space**.

###### Example

```console
$ sudo dockerd -s btrfs --storage-opt btrfs.min_space=10G
```

#### Overlay2 options

##### `overlay2.size`

Sets the default max size of the container. It is supported only when the
backing fs is `xfs` and mounted with `pquota` mount option. Under these
conditions the user can pass any size less than the backing fs size.

###### Example

```console
$ sudo dockerd -s overlay2 --storage-opt overlay2.size=1G
```


#### Windowsfilter options

##### `size`

Specifies the size to use when creating the sandbox which is used for containers.
Defaults to 20G.

###### Example

```powershell
C:\> dockerd --storage-opt size=40G
```

### Docker runtime execution options

The Docker daemon relies on a
[OCI](https://github.com/opencontainers/runtime-spec) compliant runtime
(invoked via the `containerd` daemon) as its interface to the Linux
kernel `namespaces`, `cgroups`, and `SELinux`.

By default, the Docker daemon automatically starts `containerd`. If you want to
control `containerd` startup, manually start `containerd` and pass the path to
the `containerd` socket using the `--containerd` flag. For example:

```console
$ sudo dockerd --containerd /var/run/dev/docker-containerd.sock
```

Runtimes can be registered with the daemon either via the
configuration file or using the `--add-runtime` command line argument.

The following is an example adding 2 runtimes via the configuration:

```json
{
  "default-runtime": "runc",
  "runtimes": {
    "custom": {
      "path": "/usr/local/bin/my-runc-replacement",
      "runtimeArgs": [
        "--debug"
      ]
    },
    "runc": {
      "path": "runc"
    }
  }
}
```

This is the same example via the command line:

```console
$ sudo dockerd --add-runtime runc=runc --add-runtime custom=/usr/local/bin/my-runc-replacement
```

> **Note**
>
> Defining runtime arguments via the command line is not supported.

#### Options for the runtime

You can configure the runtime using options specified
with the `--exec-opt` flag. All the flag's options have the `native` prefix. A
single `native.cgroupdriver` option is available.

The `native.cgroupdriver` option specifies the management of the container's
cgroups. You can only specify `cgroupfs` or `systemd`. If you specify
`systemd` and it is not available, the system errors out. If you omit the
`native.cgroupdriver` option,` cgroupfs` is used on cgroup v1 hosts, `systemd`
is used on cgroup v2 hosts with systemd available.

This example sets the `cgroupdriver` to `systemd`:

```console
$ sudo dockerd --exec-opt native.cgroupdriver=systemd
```

Setting this option applies to all containers the daemon launches.

Also Windows Container makes use of `--exec-opt` for special purpose. Docker user
can specify default container isolation technology with this, for example:

```console
> dockerd --exec-opt isolation=hyperv
```

Will make `hyperv` the default isolation technology on Windows. If no isolation
value is specified on daemon start, on Windows client, the default is
`hyperv`, and on Windows server, the default is `process`.

### Daemon DNS options

To set the DNS server for all Docker containers, use:

```console
$ sudo dockerd --dns 8.8.8.8
```

To set the DNS search domain for all Docker containers, use:

```console
$ sudo dockerd --dns-search example.com
```

### Allow push of nondistributable artifacts

Some images (e.g., Windows base images) contain artifacts whose distribution is
restricted by license. When these images are pushed to a registry, restricted
artifacts are not included.

To override this behavior for specific registries, use the
`--allow-nondistributable-artifacts` option in one of the following forms:

* `--allow-nondistributable-artifacts myregistry:5000` tells the Docker daemon
  to push nondistributable artifacts to myregistry:5000.
* `--allow-nondistributable-artifacts 10.1.0.0/16` tells the Docker daemon to
  push nondistributable artifacts to all registries whose resolved IP address
  is within the subnet described by the CIDR syntax.

This option can be used multiple times.

This option is useful when pushing images containing nondistributable artifacts
to a registry on an air-gapped network so hosts on that network can pull the
images without connecting to another server.

> **Warning**: Nondistributable artifacts typically have restrictions on how
> and where they can be distributed and shared. Only use this feature to push
> artifacts to private registries and ensure that you are in compliance with
> any terms that cover redistributing nondistributable artifacts.

### Insecure registries

Docker considers a private registry either secure or insecure. In the rest of
this section, *registry* is used for *private registry*, and `myregistry:5000`
is a placeholder example for a private registry.

A secure registry uses TLS and a copy of its CA certificate is placed on the
Docker host at `/etc/docker/certs.d/myregistry:5000/ca.crt`. An insecure
registry is either not using TLS (i.e., listening on plain text HTTP), or is
using TLS with a CA certificate not known by the Docker daemon. The latter can
happen when the certificate was not found under
`/etc/docker/certs.d/myregistry:5000/`, or if the certificate verification
failed (i.e., wrong CA).

By default, Docker assumes all, but local (see local registries below),
registries are secure. Communicating with an insecure registry is not possible
if Docker assumes that registry is secure. In order to communicate with an
insecure registry, the Docker daemon requires `--insecure-registry` in one of
the following two forms:

* `--insecure-registry myregistry:5000` tells the Docker daemon that
  myregistry:5000 should be considered insecure.
* `--insecure-registry 10.1.0.0/16` tells the Docker daemon that all registries
  whose domain resolve to an IP address is part of the subnet described by the
  CIDR syntax, should be considered insecure.

The flag can be used multiple times to allow multiple registries to be marked
as insecure.

If an insecure registry is not marked as insecure, `docker pull`,
`docker push`, and `docker search` will result in an error message prompting
the user to either secure or pass the `--insecure-registry` flag to the Docker
daemon as described above.

Local registries, whose IP address falls in the 127.0.0.0/8 range, are
automatically marked as insecure as of Docker 1.3.2. It is not recommended to
rely on this, as it may change in the future.

Enabling `--insecure-registry`, i.e., allowing un-encrypted and/or untrusted
communication, can be useful when running a local registry.  However,
because its use creates security vulnerabilities it should ONLY be enabled for
testing purposes.  For increased security, users should add their CA to their
system's list of trusted CAs instead of enabling `--insecure-registry`.

#### Legacy Registries

Operations against registries supporting only the legacy v1 protocol are no longer
supported. Specifically, the daemon will not attempt `push`, `pull` and `login`
to v1 registries. The exception to this is `search` which can still be performed
on v1 registries.


### Running a Docker daemon behind an HTTPS_PROXY

When running inside a LAN that uses an `HTTPS` proxy, the Docker Hub
certificates will be replaced by the proxy's certificates. These certificates
need to be added to your Docker host's configuration:

1. Install the `ca-certificates` package for your distribution
2. Ask your network admin for the proxy's CA certificate and append them to
   `/etc/pki/tls/certs/ca-bundle.crt`
3. Then start your Docker daemon with `HTTPS_PROXY=http://username:password@proxy:port/ dockerd`.
   The `username:` and `password@` are optional - and are only needed if your
   proxy is set up to require authentication.

This will only add the proxy and authentication to the Docker daemon's requests -
your `docker build`s and running containers will need extra configuration to
use the proxy

### Default `ulimit` settings

`--default-ulimit` allows you to set the default `ulimit` options to use for
all containers. It takes the same options as `--ulimit` for `docker run`. If
these defaults are not set, `ulimit` settings will be inherited, if not set on
`docker run`, from the Docker daemon. Any `--ulimit` options passed to
`docker run` will overwrite these defaults.

Be careful setting `nproc` with the `ulimit` flag as `nproc` is designed by Linux to
set the maximum number of processes available to a user, not to a container. For details
please check the [run](run.md) reference.

### Access authorization

Docker's access authorization can be extended by authorization plugins that your
organization can purchase or build themselves. You can install one or more
authorization plugins when you start the Docker `daemon` using the
`--authorization-plugin=PLUGIN_ID` option.

```console
$ sudo dockerd --authorization-plugin=plugin1 --authorization-plugin=plugin2,...
```

The `PLUGIN_ID` value is either the plugin's name or a path to its specification
file. The plugin's implementation determines whether you can specify a name or
path. Consult with your Docker administrator to get information about the
plugins available to you.

Once a plugin is installed, requests made to the `daemon` through the
command line or Docker's Engine API are allowed or denied by the plugin.
If you have multiple plugins installed, each plugin, in order, must
allow the request for it to complete.

For information about how to create an authorization plugin, refer to the
[authorization plugin](../../extend/plugins_authorization.md) section.


### Daemon user namespace options

The Linux kernel
[user namespace support](https://man7.org/linux/man-pages/man7/user_namespaces.7.html)
provides additional security by enabling a process, and therefore a container,
to have a unique range of user and group IDs which are outside the traditional
user and group range utilized by the host system. Potentially the most important
security improvement is that, by default, container processes running as the
`root` user will have expected administrative privilege (with some restrictions)
inside the container but will effectively be mapped to an unprivileged `uid` on
the host.

For details about how to use this feature, as well as limitations, see
[Isolate containers with a user namespace](https://docs.docker.com/engine/security/userns-remap/).

### Miscellaneous options

IP masquerading uses address translation to allow containers without a public
IP to talk to other machines on the Internet. This may interfere with some
network topologies and can be disabled with `--ip-masq=false`.

Docker supports softlinks for the Docker data directory (`/var/lib/docker`) and
for `/var/lib/docker/tmp`. The `DOCKER_TMPDIR` and the data directory can be
set like this:

```console
$ DOCKER_TMPDIR=/mnt/disk2/tmp /usr/local/bin/dockerd --data-root /var/lib/docker -H unix:// > /var/lib/docker-machine/docker.log 2>&1
```

or

```console
$ export DOCKER_TMPDIR=/mnt/disk2/tmp
$ /usr/local/bin/dockerd --data-root /var/lib/docker -H unix:// > /var/lib/docker-machine/docker.log 2>&1
````

#### Default cgroup parent

The `--cgroup-parent` option allows you to set the default cgroup parent
to use for containers. If this option is not set, it defaults to `/docker` for
fs cgroup driver and `system.slice` for systemd cgroup driver.

If the cgroup has a leading forward slash (`/`), the cgroup is created
under the root cgroup, otherwise the cgroup is created under the daemon
cgroup.

Assuming the daemon is running in cgroup `daemoncgroup`,
`--cgroup-parent=/foobar` creates a cgroup in
`/sys/fs/cgroup/memory/foobar`, whereas using `--cgroup-parent=foobar`
creates the cgroup in `/sys/fs/cgroup/memory/daemoncgroup/foobar`

The systemd cgroup driver has different rules for `--cgroup-parent`. Systemd
represents hierarchy by slice and the name of the slice encodes the location in
the tree. So `--cgroup-parent` for systemd cgroups should be a slice name. A
name can consist of a dash-separated series of names, which describes the path
to the slice from the root slice. For example, `--cgroup-parent=user-a-b.slice`
means the memory cgroup for the container is created in
`/sys/fs/cgroup/memory/user.slice/user-a.slice/user-a-b.slice/docker-<id>.scope`.

This setting can also be set per container, using the `--cgroup-parent`
option on `docker create` and `docker run`, and takes precedence over
the `--cgroup-parent` option on the daemon.

#### Daemon metrics

The `--metrics-addr` option takes a tcp address to serve the metrics API.
This feature is still experimental, therefore, the daemon must be running in experimental
mode for this feature to work.

To serve the metrics API on `localhost:9323` you would specify `--metrics-addr 127.0.0.1:9323`,
allowing you to make requests on the API at `127.0.0.1:9323/metrics` to receive metrics in the
[prometheus](https://prometheus.io/docs/instrumenting/exposition_formats/) format.

Port `9323` is the [default port associated with Docker
metrics](https://github.com/prometheus/prometheus/wiki/Default-port-allocations)
to avoid collisions with other prometheus exporters and services.

If you are running a prometheus server you can add this address to your scrape configs
to have prometheus collect metrics on Docker.  For more information
on prometheus refer to the [prometheus website](https://prometheus.io/).

```yaml
scrape_configs:
  - job_name: 'docker'
    static_configs:
      - targets: ['127.0.0.1:9323']
```

Please note that this feature is still marked as experimental as metrics and metric
names could change while this feature is still in experimental.  Please provide
feedback on what you would like to see collected in the API.

#### Node Generic Resources

The `--node-generic-resources` option takes a list of key-value
pair (`key=value`) that allows you to advertise user defined resources
in a swarm cluster.

The current expected use case is to advertise NVIDIA GPUs so that services
requesting `NVIDIA-GPU=[0-16]` can land on a node that has enough GPUs for
the task to run.

Example of usage:
```json
{
  "node-generic-resources": [
    "NVIDIA-GPU=UUID1",
    "NVIDIA-GPU=UUID2"
  ]
}
```

### Daemon configuration file

The `--config-file` option allows you to set any configuration option
for the daemon in a JSON format. This file uses the same flag names as keys,
except for flags that allow several entries, where it uses the plural
of the flag name, e.g., `labels` for the `label` flag.

The options set in the configuration file must not conflict with options set
via flags. The docker daemon fails to start if an option is duplicated between
the file and the flags, regardless of their value. We do this to avoid
silently ignore changes introduced in configuration reloads.
For example, the daemon fails to start if you set daemon labels
in the configuration file and also set daemon labels via the `--label` flag.
Options that are not present in the file are ignored when the daemon starts.

The `--validate` option allows to validate a configuration file without
starting the Docker daemon. A non-zero exit code is returned for invalid
configuration files.

```console
$ dockerd --validate --config-file=/tmp/valid-config.json
configuration OK

$ echo $?
0

$ dockerd --validate --config-file /tmp/invalid-config.json
unable to configure the Docker daemon with file /tmp/invalid-config.json: the following directives don't match any configuration option: unknown-option

$ echo $?
1
```


##### On Linux

The default location of the configuration file on Linux is
`/etc/docker/daemon.json`. The `--config-file` flag can be used to specify a
 non-default location.

This is a full example of the allowed configuration options on Linux:

```json
{
  "allow-nondistributable-artifacts": [],
  "api-cors-header": "",
  "authorization-plugins": [],
  "bip": "",
  "bridge": "",
  "cgroup-parent": "",
  "containerd": "/run/containerd/containerd.sock",
  "containerd-namespace": "docker",
  "containerd-plugin-namespace": "docker-plugins",
  "data-root": "",
  "debug": true,
  "default-address-pools": [
    {
      "base": "172.30.0.0/16",
      "size": 24
    },
    {
      "base": "172.31.0.0/16",
      "size": 24
    }
  ],
  "default-cgroupns-mode": "private",
  "default-gateway": "",
  "default-gateway-v6": "",
  "default-runtime": "runc",
  "default-shm-size": "64M",
  "default-ulimits": {
    "nofile": {
      "Hard": 64000,
      "Name": "nofile",
      "Soft": 64000
    }
  },
  "dns": [],
  "dns-opts": [],
  "dns-search": [],
  "exec-opts": [],
  "exec-root": "",
  "experimental": false,
  "features": {},
  "fixed-cidr": "",
  "fixed-cidr-v6": "",
  "group": "",
  "hosts": [],
  "proxies": {
    "http-proxy": "http://proxy.example.com:80",
    "https-proxy": "https://proxy.example.com:443",
    "no-proxy": "*.test.example.com,.example.org",
  },
  "icc": false,
  "init": false,
  "init-path": "/usr/libexec/docker-init",
  "insecure-registries": [],
  "ip": "0.0.0.0",
  "ip-forward": false,
  "ip-masq": false,
  "iptables": false,
  "ip6tables": false,
  "ipv6": false,
  "labels": [],
  "live-restore": true,
  "log-driver": "json-file",
  "log-level": "",
  "log-opts": {
    "cache-disabled": "false",
    "cache-max-file": "5",
    "cache-max-size": "20m",
    "cache-compress": "true",
    "env": "os,customer",
    "labels": "somelabel",
    "max-file": "5",
    "max-size": "10m"
  },
  "max-concurrent-downloads": 3,
  "max-concurrent-uploads": 5,
  "max-download-attempts": 5,
  "mtu": 0,
  "no-new-privileges": false,
  "node-generic-resources": [
    "NVIDIA-GPU=UUID1",
    "NVIDIA-GPU=UUID2"
  ],
  "oom-score-adjust": 0,
  "pidfile": "",
  "raw-logs": false,
  "registry-mirrors": [],
  "runtimes": {
    "cc-runtime": {
      "path": "/usr/bin/cc-runtime"
    },
    "custom": {
      "path": "/usr/local/bin/my-runc-replacement",
      "runtimeArgs": [
        "--debug"
      ]
    }
  },
  "seccomp-profile": "",
  "selinux-enabled": false,
  "shutdown-timeout": 15,
  "storage-driver": "",
  "storage-opts": [],
  "swarm-default-advertise-addr": "",
  "tls": true,
  "tlscacert": "",
  "tlscert": "",
  "tlskey": "",
  "tlsverify": true,
  "userland-proxy": false,
  "userland-proxy-path": "/usr/libexec/docker-proxy",
  "userns-remap": ""
}
```

> **Note:**
>
> You cannot set options in `daemon.json` that have already been set on
> daemon startup as a flag.
> On systems that use `systemd` to start the Docker daemon, `-H` is already set, so
> you cannot use the `hosts` key in `daemon.json` to add listening addresses.
> See ["custom Docker daemon options"](https://docs.docker.com/config/daemon/systemd/#custom-docker-daemon-options) for how
> to accomplish this task with a systemd drop-in file.

##### On Windows

The default location of the configuration file on Windows is
 `%programdata%\docker\config\daemon.json`. The `--config-file` flag can be
 used to specify a non-default location.

This is a full example of the allowed configuration options on Windows:

```json
{
  "allow-nondistributable-artifacts": [],
  "authorization-plugins": [],
  "bridge": "",
  "containerd": "\\\\.\\pipe\\containerd-containerd",
  "containerd-namespace": "docker",
  "containerd-plugin-namespace": "docker-plugins",
  "data-root": "",
  "debug": true,
  "default-runtime": "",
  "default-ulimits": {},
  "dns": [],
  "dns-opts": [],
  "dns-search": [],
  "exec-opts": [],
  "experimental": false,
  "features": {},
  "fixed-cidr": "",
  "group": "",
  "hosts": [],
  "insecure-registries": [],
  "labels": [],
  "log-driver": "",
  "log-level": "",
  "max-concurrent-downloads": 3,
  "max-concurrent-uploads": 5,
  "max-download-attempts": 5,
  "mtu": 0,
  "pidfile": "",
  "raw-logs": false,
  "registry-mirrors": [],
  "shutdown-timeout": 15,
  "storage-driver": "",
  "storage-opts": [],
  "swarm-default-advertise-addr": "",
  "tlscacert": "",
  "tlscert": "",
  "tlskey": "",
  "tlsverify": true
}
```

The `default-runtime` option is by default unset, in which case dockerd will auto-detect the runtime. This detection is currently based on if the `containerd` flag is set.

Accepted values:

- `com.docker.hcsshim.v1` - This is the built-in runtime that Docker has used since Windows supported was first added and uses the v1 HCS API's in Windows.
- `io.containerd.runhcs.v1` - This is uses the containerd `runhcs` shim to run the container and uses the v2 HCS API's in Windows.

#### Feature options
The optional field `features` in `daemon.json` allows users to enable or disable specific
daemon features. For example, `{"features":{"buildkit": true}}` enables `buildkit` as the
default docker image builder.

The list of currently supported feature options:
- `buildkit`: It enables `buildkit` as default builder when set to `true` or disables it by
`false`. Note that if this option is not explicitly set in the daemon config file, then it
is up to the cli to determine which builder to invoke.

#### Configuration reload behavior

Some options can be reconfigured when the daemon is running without requiring
to restart the process. We use the `SIGHUP` signal in Linux to reload, and a global event
in Windows with the key `Global\docker-daemon-config-$PID`. The options can
be modified in the configuration file but still will check for conflicts with
the provided flags. The daemon fails to reconfigure itself
if there are conflicts, but it won't stop execution.

The list of currently supported options that can be reconfigured is this:

- `debug`: it changes the daemon to debug mode when set to true.
- `labels`: it replaces the daemon labels with a new set of labels.
- `live-restore`: Enables [keeping containers alive during daemon downtime](https://docs.docker.com/config/containers/live-restore/).
- `max-concurrent-downloads`: it updates the max concurrent downloads for each pull.
- `max-concurrent-uploads`: it updates the max concurrent uploads for each push.
- `max-download-attempts`: it updates the max download attempts for each pull.
- `default-runtime`: it updates the runtime to be used if not is
  specified at container creation. It defaults to "default" which is
  the runtime shipped with the official docker packages.
- `runtimes`: it updates the list of available OCI runtimes that can
  be used to run containers.
- `authorization-plugin`: it specifies the authorization plugins to use.
- `allow-nondistributable-artifacts`: Replaces the set of registries to which the daemon will push nondistributable artifacts with a new set of registries.
- `insecure-registries`: it replaces the daemon insecure registries with a new set of insecure registries. If some existing insecure registries in daemon's configuration are not in newly reloaded insecure registries, these existing ones will be removed from daemon's config.
- `registry-mirrors`: it replaces the daemon registry mirrors with a new set of registry mirrors. If some existing registry mirrors in daemon's configuration are not in newly reloaded registry mirrors, these existing ones will be removed from daemon's config.
- `shutdown-timeout`: it replaces the daemon's existing configuration timeout with a new timeout for shutting down all containers.
- `features`: it explicitly enables or disables specific features.

### Run multiple daemons

> **Note:**
>
> Running multiple daemons on a single host is considered as "experimental". The user should be aware of
> unsolved problems. This solution may not work properly in some cases. Solutions are currently under development
> and will be delivered in the near future.

This section describes how to run multiple Docker daemons on a single host. To
run multiple daemons, you must configure each daemon so that it does not
conflict with other daemons on the same host. You can set these options either
by providing them as flags, or by using a [daemon configuration file](#daemon-configuration-file).

The following daemon options must be configured for each daemon:

```console
-b, --bridge=                          Attach containers to a network bridge
--exec-root=/var/run/docker            Root of the Docker execdriver
--data-root=/var/lib/docker            Root of persisted Docker data
-p, --pidfile=/var/run/docker.pid      Path to use for daemon PID file
-H, --host=[]                          Daemon socket(s) to connect to
--iptables=true                        Enable addition of iptables rules
--config-file=/etc/docker/daemon.json  Daemon configuration file
--tlscacert="~/.docker/ca.pem"         Trust certs signed only by this CA
--tlscert="~/.docker/cert.pem"         Path to TLS certificate file
--tlskey="~/.docker/key.pem"           Path to TLS key file
```

When your daemons use different values for these flags, you can run them on the same host without any problems.
It is very important to properly understand the meaning of those options and to use them correctly.

- The `-b, --bridge=` flag is set to `docker0` as default bridge network. It is created automatically when you install Docker.
If you are not using the default, you must create and configure the bridge manually or just set it to 'none': `--bridge=none`
- `--exec-root` is the path where the container state is stored. The default value is `/var/run/docker`. Specify the path for
your running daemon here.
- `--data-root` is the path where persisted data such as images, volumes, and
cluster state are stored. The default value is `/var/lib/docker`. To avoid any
conflict with other daemons, set this parameter separately for each daemon.
- `-p, --pidfile=/var/run/docker.pid` is the path where the process ID of the daemon is stored. Specify the path for your
pid file here.
- `--host=[]` specifies where the Docker daemon will listen for client connections. If unspecified, it defaults to `/var/run/docker.sock`.
-  `--iptables=false` prevents the Docker daemon from adding iptables rules. If
multiple daemons manage iptables rules, they may overwrite rules set by another
daemon. Be aware that disabling this option requires you to manually add
iptables rules to expose container ports. If you prevent Docker from adding
iptables rules, Docker will also not add IP masquerading rules, even if you set
`--ip-masq` to `true`. Without IP masquerading rules, Docker containers will not be
able to connect to external hosts or the internet when using network other than
default bridge.
- `--config-file=/etc/docker/daemon.json` is the path where configuration file is stored. You can use it instead of
daemon flags. Specify the path for each daemon.
- `--tls*` Docker daemon supports `--tlsverify` mode that enforces encrypted and authenticated remote connections.
The `--tls*` options enable use of specific certificates for individual daemons.

Example script for a separate “bootstrap” instance of the Docker daemon without network:

```console
$ sudo dockerd \
        -H unix:///var/run/docker-bootstrap.sock \
        -p /var/run/docker-bootstrap.pid \
        --iptables=false \
        --ip-masq=false \
        --bridge=none \
        --data-root=/var/lib/docker-bootstrap \
        --exec-root=/var/run/docker-bootstrap
```