Provided by: docker.io_1.10.3-0ubuntu6_amd64 bug


       docker-daemon - Enable daemon mode


       docker daemon [--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]] [-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[=]] [--ip-forward[=true]] [--ip-masq[=true]]
       [--iptables[=true]] [--ipv6] [-l|--log-level[=info]] [--label[=[]]]
       [--log-driver[=json-file]] [--log-opt[=map[]]] [--mtu[=0]]
       [-p|--pidfile[=/var/run/]] [--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]]


       docker has two distinct functions. It is used for starting the Docker daemon and to run
       the CLI (i.e., to command the daemon to manage images, containers etc.) So docker is both
       a server, as a daemon, and a client to the daemon, through the CLI.

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

       docker daemon [OPTIONS]


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

         Set authorization plugins to load

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

         Use the provided CIDR notation address for the dynamically created bridge (docker0);
       Mutually exclusive of -b

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

         URL of the distributed storage backend

         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.

         Specifies options for the Key/Value store.

         Specifies the JSON file path to load the configuration from.

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

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

         IPv6 address of the container default gateway

         Set default ulimits for containers.

         Do not contact legacy registries

         Force Docker to use specific DNS servers

         DNS options to use.

         DNS search domains to use.

         Set exec driver options. See EXEC DRIVER OPTIONS.

         Path to use as the root of the Docker exec driver. Default is /var/run/docker.

         IPv4 subnet for fixed IPs (e.g.,; this subnet must be nested in the bridge
       subnet (which is defined by -b or --bip)

         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.

         Print usage statement

         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.

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

       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

       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.

         Default IP address to use when binding container ports. Default is

         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".

         Enable IP masquerading for bridge's IP range. Default is true.

         Enable Docker's addition of iptables rules. Default is true.

         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".

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

         Set key=value labels to the daemon (displayed in docker info)

         Default driver for container logs. Default is json-file.
         Warning: docker logs command works only for json-file logging driver.

         Logging driver specific options.

         Set the containers network mtu. Default is 0.

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

         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.

         Enable selinux support. Default is false. SELinux does not presently support the overlay
       storage driver.

         Set storage driver options. See STORAGE DRIVER OPTIONS.

         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.

         Use TLS and verify the remote (daemon: verify client, client: verify daemon).
         Default is false.

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

           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.


       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 only backend that
       currently takes options is devicemapper. Therefore use these flags with -s=devicemapper.

       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.

       Here is the list of devicemapper options:

       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 create snapshot
       volumes needed for images and containers.

       Managing the thin-pool outside of Docker makes for the most feature-rich method of having
       Docker utilize device mapper thin provisioning as the backing storage for Docker's
       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.

       Example use: docker daemon --storage-opt dm.thinpooldev=/dev/mapper/thin-pool

       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: docker daemon --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: docker daemon --storage-opt dm.basesize=20G

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

       Example use: docker daemon --storage-opt dm.fs=xfs

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

       Example use: docker daemon --storage-opt "dm.mkfsarg=-O ^has_journal"

       Specifies extra mount options used when mounting the thin devices.

       Example use: docker daemon --storage-opt dm.mountopt=nodiscard

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

       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: docker daemon --storage-opt dm.use_deferred_removal=true

       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.

       docker daemon --storage-opt dm.use_deferred_deletion=true --storage-opt

       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.

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

       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: docker daemon --storage-opt dm.loopdatasize=200G

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

       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: docker daemon --storage-opt dm.loopmetadatasize=4G

       (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

       (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.

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

       Example use: docker daemon --storage-opt dm.blocksize=512K

       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

       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: docker daemon --storage-opt dm.blkdiscard=false

       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,

                  $ 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


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

                  $ docker daemon --storage-opt dm.override_udev_sync_check=true

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

       Note: The ideal is to pursue a docker daemon and environment that does support
       synchronizing with udev. For further discussion on this topic, see

       ⟨⟩.  Otherwise, set this flag for migrating
       existing Docker daemons to a daemon with a supported environment.


       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.

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

       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.

       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

              docker daemon --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
       ⟨⟩ section in the Docker extend
       section of this documentation.


       Sept 2015, Originally compiled by Shishir Mahajan ⟨⟩ based on source material and internal work.