% DOCKER(8) Docker User Manuals
% Shishir Mahajan
% SEPTEMBER 2015
# NAME
dockerd - Enable daemon mode

# SYNOPSIS
**dockerd**
[**--api-cors-header**=[=*API-CORS-HEADER*]]
[**--authorization-plugin**[=*[]*]]
[**-b**|**--bridge**[=*BRIDGE*]]
[**--bip**[=*BIP*]]
[**--cgroup-parent**[=*[]*]]
[**--cluster-store**[=*[]*]]
[**--cluster-advertise**[=*[]*]]
[**--cluster-store-opt**[=*map[]*]]
[**--config-file**[=*/etc/docker/daemon.json*]]
[**--containerd**[=*SOCKET-PATH*]]
[**-D**|**--debug**]
[**--default-gateway**[=*DEFAULT-GATEWAY*]]
[**--default-gateway-v6**[=*DEFAULT-GATEWAY-V6*]]
[**--default-ulimit**[=*[]*]]
[**--disable-legacy-registry**]
[**--dns**[=*[]*]]
[**--dns-opt**[=*[]*]]
[**--dns-search**[=*[]*]]
[**--exec-opt**[=*[]*]]
[**--exec-root**[=*/var/run/docker*]]
[**--fixed-cidr**[=*FIXED-CIDR*]]
[**--fixed-cidr-v6**[=*FIXED-CIDR-V6*]]
[**-G**|**--group**[=*docker*]]
[**-g**|**--graph**[=*/var/lib/docker*]]
[**-H**|**--host**[=*[]*]]
[**--help**]
[**--icc**[=*true*]]
[**--insecure-registry**[=*[]*]]
[**--ip**[=*0.0.0.0*]]
[**--ip-forward**[=*true*]]
[**--ip-masq**[=*true*]]
[**--iptables**[=*true*]]
[**--ipv6**]
[**--isolation**[=*default*]]
[**-l**|**--log-level**[=*info*]]
[**--label**[=*[]*]]
[**--log-driver**[=*json-file*]]
[**--log-opt**[=*map[]*]]
[**--mtu**[=*0*]]
[**--max-concurrent-downloads**[=*3*]]
[**--max-concurrent-uploads**[=*5*]]
[**-p**|**--pidfile**[=*/var/run/docker.pid*]]
[**--raw-logs**]
[**--registry-mirror**[=*[]*]]
[**-s**|**--storage-driver**[=*STORAGE-DRIVER*]]
[**--selinux-enabled**]
[**--storage-opt**[=*[]*]]
[**--tls**]
[**--tlscacert**[=*~/.docker/ca.pem*]]
[**--tlscert**[=*~/.docker/cert.pem*]]
[**--tlskey**[=*~/.docker/key.pem*]]
[**--tlsverify**]
[**--userland-proxy**[=*true*]]
[**--userns-remap**[=*default*]]

# DESCRIPTION
**dockerd** is used for starting the Docker daemon(i.e., to command the daemon to manage images,
containers etc.) So **dockerd** is a server, as a daemon.

To run the Docker daemon you can specify **dockerd**.
You can check the daemon options using **dockerd --help**.
Daemon options should be specified after the **dockerd** keyword in the following
format.

**dockerd [OPTIONS]**

# OPTIONS

**--api-cors-header**=""
  Set CORS headers in the remote API. Default is cors disabled. Give urls like "http://foo, http://bar, ...". Give "*" to allow all.

**--authorization-plugin**=""
  Set authorization plugins to load

**-b**, **--bridge**=""
  Attach containers to a pre\-existing network bridge; use 'none' to disable container networking

**--bip**=""
  Use the provided CIDR notation address for the dynamically created bridge (docker0); Mutually exclusive of \-b

**--cgroup-parent**=""
  Set parent cgroup for all containers. Default is "/docker" for fs cgroup driver and "system.slice" for systemd cgroup driver.

**--cluster-store**=""
  URL of the distributed storage backend

**--cluster-advertise**=""
  Specifies the 'host:port' or `interface:port` combination that this particular
  daemon instance should use when advertising itself to the cluster. The daemon
  is reached through this value.

**--cluster-store-opt**=""
  Specifies options for the Key/Value store.

**--config-file**="/etc/docker/daemon.json"
  Specifies the JSON file path to load the configuration from.

**--containerd**=""
  Path to containerd socket.

**-D**, **--debug**=*true*|*false*
  Enable debug mode. Default is false.

**--default-gateway**=""
  IPv4 address of the container default gateway; this address must be part of the bridge subnet (which is defined by \-b or \--bip)

**--default-gateway-v6**=""
  IPv6 address of the container default gateway

**--default-ulimit**=[]
  Set default ulimits for containers.

**--disable-legacy-registry**=*true*|*false*
  Do not contact legacy registries

**--dns**=""
  Force Docker to use specific DNS servers

**--dns-opt**=""
  DNS options to use.

**--dns-search**=[]
  DNS search domains to use.

**--exec-opt**=[]
  Set runtime execution options. See RUNTIME EXECUTION OPTIONS.

**--exec-root**=""
  Path to use as the root of the Docker execution state files. Default is `/var/run/docker`.

**--fixed-cidr**=""
  IPv4 subnet for fixed IPs (e.g., 10.20.0.0/16); this subnet must be nested in the bridge subnet (which is defined by \-b or \-\-bip)

**--fixed-cidr-v6**=""
  IPv6 subnet for global IPv6 addresses (e.g., 2a00:1450::/64)

**-G**, **--group**=""
  Group to assign the unix socket specified by -H when running in daemon mode.
  use '' (the empty string) to disable setting of a group. Default is `docker`.

**-g**, **--graph**=""
  Path to use as the root of the Docker runtime. Default is `/var/lib/docker`.

**-H**, **--host**=[*unix:///var/run/docker.sock*]: tcp://[host:port] to bind or
unix://[/path/to/socket] to use.
  The socket(s) to bind to in daemon mode specified using one or more
  tcp://host:port, unix:///path/to/socket, fd://* or fd://socketfd.

**--help**
  Print usage statement

**--icc**=*true*|*false*
  Allow unrestricted inter\-container and Docker daemon host communication. If disabled, containers can still be linked together using the **--link** option (see **docker-run(1)**). Default is true.

**--insecure-registry**=[]
  Enable insecure registry communication, i.e., enable un-encrypted and/or untrusted communication.

  List of insecure registries can contain an element with CIDR notation to specify a whole subnet. Insecure registries accept HTTP and/or accept HTTPS with certificates from unknown CAs.

  Enabling `--insecure-registry` is 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 using `--insecure-registry`.

**--ip**=""
  Default IP address to use when binding container ports. Default is `0.0.0.0`.

**--ip-forward**=*true*|*false*
  Enables IP forwarding on the Docker host. The default is `true`. This flag interacts with the IP forwarding setting on your host system's kernel. If your system has IP forwarding disabled, this setting enables it. If your system has IP forwarding enabled, setting this flag to `--ip-forward=false` has no effect.

  This setting will also enable IPv6 forwarding if you have both `--ip-forward=true` and `--fixed-cidr-v6` set. Note that this may reject Router Advertisements and interfere with the host's existing IPv6 configuration. For more information, please consult the documentation about "Advanced Networking - IPv6".

**--ip-masq**=*true*|*false*
  Enable IP masquerading for bridge's IP range. Default is true.

**--iptables**=*true*|*false*
  Enable Docker's addition of iptables rules. Default is true.

**--ipv6**=*true*|*false*
  Enable IPv6 support. Default is false. Docker will create an IPv6-enabled bridge with address fe80::1 which will allow you to create IPv6-enabled containers. Use together with `--fixed-cidr-v6` to provide globally routable IPv6 addresses. IPv6 forwarding will be enabled if not used with `--ip-forward=false`. This may collide with your host's current IPv6 settings. For more information please consult the documentation about "Advanced Networking - IPv6".

**--isolation**="*default*"
   Isolation specifies the type of isolation technology used by containers. Note
that the default on Windows server is `process`, and the default on Windows client
is `hyperv`. Linux only supports `default`.

**-l**, **--log-level**="*debug*|*info*|*warn*|*error*|*fatal*"
  Set the logging level. Default is `info`.

**--label**="[]"
  Set key=value labels to the daemon (displayed in `docker info`)

**--log-driver**="*json-file*|*syslog*|*journald*|*gelf*|*fluentd*|*awslogs*|*splunk*|*etwlogs*|*gcplogs*|*none*"
  Default driver for container logs. Default is `json-file`.
  **Warning**: `docker logs` command works only for `json-file` logging driver.

**--log-opt**=[]
  Logging driver specific options.

**--mtu**=*0*
  Set the containers network mtu. Default is `0`.

**--max-concurrent-downloads**=*3*
  Set the max concurrent downloads for each pull. Default is `3`.

**--max-concurrent-uploads**=*5*
  Set the max concurrent uploads for each push. Default is `5`.

**-p**, **--pidfile**=""
  Path to use for daemon PID file. Default is `/var/run/docker.pid`

**--raw-logs**
Output daemon logs in full timestamp format without ANSI coloring. If this flag is not set,
the daemon outputs condensed, colorized logs if a terminal is detected, or full ("raw")
output otherwise.

**--registry-mirror**=*<scheme>://<host>*
  Prepend a registry mirror to be used for image pulls. May be specified multiple times.

**-s**, **--storage-driver**=""
  Force the Docker runtime to use a specific storage driver.

**--selinux-enabled**=*true*|*false*
  Enable selinux support. Default is false. SELinux does not presently support the overlay storage driver.

**--storage-opt**=[]
  Set storage driver options. See STORAGE DRIVER OPTIONS.

**--tls**=*true*|*false*
  Use TLS; implied by --tlsverify. Default is false.

**--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.

**--tlsverify**=*true*|*false*
  Use TLS and verify the remote (daemon: verify client, client: verify daemon).
  Default is false.

**--userland-proxy**=*true*|*false*
    Rely on a userland proxy implementation for inter-container and outside-to-container loopback communications. Default is true.

**--userns-remap**=*default*|*uid:gid*|*user:group*|*user*|*uid*
    Enable user namespaces for containers on the daemon. Specifying "default" will cause a new user and group to be created to handle UID and GID range remapping for the user namespace mappings used for contained processes. Specifying a user (or uid) and optionally a group (or gid) will cause the daemon to lookup the user and group's subordinate ID ranges for use as the user namespace mappings for contained processes.

# STORAGE DRIVER OPTIONS

Docker uses storage backends (known as "graphdrivers" in the Docker
internals) to create writable containers from images.  Many of these
backends use operating system level technologies and can be
configured.

Specify options to the storage backend with **--storage-opt** flags. The
backends that currently take options are *devicemapper*, *zfs* and *btrfs*.
Options for *devicemapper* are prefixed with *dm*, options for *zfs*
start with *zfs* and options for *btrfs* start with *btrfs*.

Specifically for devicemapper, the default is a "loopback" model which
requires no pre-configuration, but is extremely inefficient.  Do not
use it in production.

To make the best use of Docker with the devicemapper backend, you must
have a recent version of LVM.  Use `lvm` to create a thin pool; for
more information see `man lvmthin`.  Then, use `--storage-opt
dm.thinpooldev` to tell the Docker engine to use that pool for
allocating images and container snapshots.

## Devicemapper options

#### dm.thinpooldev

Specifies a custom block storage device to use for the thin pool.

If using a block device for device mapper storage, it is best to use `lvm`
to create and manage the thin-pool volume. This volume is then handed to Docker
to exclusively create snapshot volumes needed for images and containers.

Managing the thin-pool outside of Engine makes for the most feature-rich
method of having Docker utilize device mapper thin provisioning as the
backing storage for Docker containers. The highlights of the lvm-based
thin-pool management feature include: automatic or interactive thin-pool
resize support, dynamically changing thin-pool features, automatic thinp
metadata checking when lvm activates the thin-pool, etc.

As a fallback if no thin pool is provided, loopback files are
created. Loopback is very slow, but can be used without any
pre-configuration of storage. It is strongly recommended that you do
not use loopback in production. Ensure your Engine daemon has a
`--storage-opt dm.thinpooldev` argument provided.

Example use:

   $ dockerd \
         --storage-opt dm.thinpooldev=/dev/mapper/thin-pool

#### dm.basesize

Specifies the size to use when creating the base device, which limits
the size of images and containers. The default value is 10G. Note,
thin devices are inherently "sparse", so a 10G device which is mostly
empty doesn't use 10 GB of space on the pool. However, the filesystem
will use more space for base images the larger the device
is.

The base device size can be increased at daemon restart which will allow
all future images and containers (based on those new images) to be of the
new base device size.

Example use: `dockerd --storage-opt dm.basesize=50G`

This will increase the base device size to 50G. The Docker daemon will throw an
error if existing base device size is larger than 50G. A user can use
this option to expand the base device size however shrinking is not permitted.

This value affects the system-wide "base" empty filesystem that may already
be initialized and inherited by pulled images. Typically, a change to this
value requires additional steps to take effect:

        $ sudo service docker stop
        $ sudo rm -rf /var/lib/docker
        $ sudo service docker start

Example use: `dockerd --storage-opt dm.basesize=20G`

#### dm.fs

Specifies the filesystem type to use for the base device. The
supported options are `ext4` and `xfs`. The default is `ext4`.

Example use: `dockerd --storage-opt dm.fs=xfs`

#### dm.mkfsarg

Specifies extra mkfs arguments to be used when creating the base device.

Example use: `dockerd --storage-opt "dm.mkfsarg=-O ^has_journal"`

#### dm.mountopt

Specifies extra mount options used when mounting the thin devices.

Example use: `dockerd --storage-opt dm.mountopt=nodiscard`

#### dm.use_deferred_removal

Enables use of deferred device removal if `libdm` and the kernel driver
support the mechanism.

Deferred device removal means that if device is busy when devices are
being removed/deactivated, then a deferred removal is scheduled on
device. And devices automatically go away when last user of the device
exits.

For example, when a container exits, its associated thin device is removed. If
that device has leaked into some other mount namespace and can't be removed,
the container exit still succeeds and this option causes the system to schedule
the device for deferred removal. It does not wait in a loop trying to remove a busy
device.

Example use: `dockerd --storage-opt dm.use_deferred_removal=true`

#### dm.use_deferred_deletion

Enables use of deferred device deletion for thin pool devices. By default,
thin pool device deletion is synchronous. Before a container is deleted, the
Docker daemon removes any associated devices. If the storage driver can not
remove a device, the container deletion fails and daemon returns.

`Error deleting container: Error response from daemon: Cannot destroy container`

To avoid this failure, enable both deferred device deletion and deferred
device removal on the daemon.

`dockerd --storage-opt dm.use_deferred_deletion=true --storage-opt dm.use_deferred_removal=true`

With these two options enabled, if a device is busy when the driver is
deleting a container, the driver marks the device as deleted. Later, when the
device isn't in use, the driver deletes it.

In general it should be safe to enable this option by default. It will help
when unintentional leaking of mount point happens across multiple mount
namespaces.

#### dm.loopdatasize

**Note**: This option configures devicemapper loopback, which should not be used in production.

Specifies the size to use when creating the loopback file for the
"data" device which is used for the thin pool. The default size is
100G. The file is sparse, so it will not initially take up
this much space.

Example use: `dockerd --storage-opt dm.loopdatasize=200G`

#### dm.loopmetadatasize

**Note**: This option configures devicemapper loopback, which should not be used in production.

Specifies the size to use when creating the loopback file for the
"metadata" device which is used for the thin pool. The default size
is 2G. The file is sparse, so it will not initially take up
this much space.

Example use: `dockerd --storage-opt dm.loopmetadatasize=4G`

#### dm.datadev

(Deprecated, use `dm.thinpooldev`)

Specifies a custom blockdevice to use for data for a
Docker-managed thin pool.  It is better to use `dm.thinpooldev` - see
the documentation for it above for discussion of the advantages.

#### dm.metadatadev

(Deprecated, use `dm.thinpooldev`)

Specifies a custom blockdevice to use for metadata for a
Docker-managed thin pool.  See `dm.datadev` for why this is
deprecated.

#### dm.blocksize

Specifies a custom blocksize to use for the thin pool.  The default
blocksize is 64K.

Example use: `dockerd --storage-opt dm.blocksize=512K`

#### dm.blkdiscard

Enables or disables the use of `blkdiscard` when removing devicemapper
devices.  This is disabled by default due to the additional latency,
but as a special case with loopback devices it will be enabled, in
order to re-sparsify the loopback file on image/container removal.

Disabling this on loopback can lead to *much* faster container removal
times, but it also prevents the space used in `/var/lib/docker` directory
from being returned to the system for other use when containers are
removed.

Example use: `dockerd --storage-opt dm.blkdiscard=false`

#### dm.override_udev_sync_check

By default, the devicemapper backend attempts to synchronize with the
`udev` device manager for the Linux kernel.  This option allows
disabling that synchronization, to continue even though the
configuration may be buggy.

To view the `udev` sync support of a Docker daemon that is using the
`devicemapper` driver, run:

        $ docker info
        [...]
         Udev Sync Supported: true
        [...]

When `udev` sync support is `true`, then `devicemapper` and `udev` can
coordinate the activation and deactivation of devices for containers.

When `udev` sync support is `false`, a race condition occurs between
the `devicemapper` and `udev` during create and cleanup. The race
condition results in errors and failures. (For information on these
failures, see
[docker#4036](https://github.com/docker/docker/issues/4036))

To allow the `docker` daemon to start, regardless of whether `udev` sync is
`false`, set `dm.override_udev_sync_check` to true:

        $ dockerd --storage-opt dm.override_udev_sync_check=true

When this value is `true`, the driver continues and simply warns you
the errors are happening.

**Note**: The ideal is to pursue a `docker` daemon and environment
that does support synchronizing with `udev`. For further discussion on
this topic, see
[docker#4036](https://github.com/docker/docker/issues/4036).
Otherwise, set this flag for migrating existing Docker daemons to a
daemon with a supported environment.

#### dm.min_free_space

Specifies the min free space percent in a thin pool require for new device
creation to succeed. This check applies to both free data space as well
as free metadata space. Valid values are from 0% - 99%. Value 0% disables
free space checking logic. If user does not specify a value for this option,
the Engine uses a default value of 10%.

Whenever a new a thin pool device is created (during `docker pull` or during
container creation), the Engine checks if the minimum free space is
available. If the space is unavailable, then device creation fails and any
relevant `docker` operation fails.

To recover from this error, you must create more free space in the thin pool to
recover from the error. You can create free space by deleting some images
and containers from tge thin pool. You can also add
more storage to the thin pool.

To add more space to an LVM (logical volume management) thin pool, just add
more storage to the  group container thin pool; this should automatically
resolve any errors. If your configuration uses loop devices, then stop the
Engine daemon, grow the size of loop files and restart the daemon to resolve
the issue.

Example use:: `dockerd --storage-opt dm.min_free_space=10%`

## 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 use: `dockerd -s zfs --storage-opt zfs.fsname=zroot/docker`

## Btrfs options

#### btrfs.min_space

Specifies the mininum 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 use: `docker daemon -s btrfs --storage-opt btrfs.min_space=10G`

# CLUSTER STORE OPTIONS

The daemon uses libkv to advertise
the node within the cluster.  Some Key/Value backends support mutual
TLS, and the client TLS settings used by the daemon can be configured
using the **--cluster-store-opt** flag, specifying the paths to PEM encoded
files.

#### kv.cacertfile

Specifies the path to a local file with PEM encoded CA certificates to trust

#### kv.certfile

Specifies the path to a local file with a PEM encoded certificate.  This
certificate is used as the client cert for communication with the
Key/Value store.

#### kv.keyfile

Specifies the path to a local file with a PEM encoded private key.  This
private key is used as the client key for communication with the
Key/Value store.

# 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.

```bash
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 remote API are allowed or denied by the plugin.  If you have
multiple plugins installed, at least one must allow the request for it to
complete.

For information about how to create an authorization plugin, see [authorization
plugin](https://docs.docker.com/engine/extend/authorization/) section in the
Docker extend section of this documentation.


# HISTORY
Sept 2015, Originally compiled by Shishir Mahajan <shishir.mahajan@redhat.com>
based on docker.com source material and internal work.
