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% DOCKER(1) Docker User Manuals % William Henry % APRIL 2014

NAME

docker - Docker image and container command line interface

SYNOPSIS

docker [OPTIONS] COMMAND [arg...]

DESCRIPTION

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 do not specify any of the commands listed below but must specify the -d option. The other options listed below are for the daemon only.

The Docker CLI has over 30 commands. The commands are listed below and each has its own man page which explain usage and arguments.

To see the man page for a command run man docker .

OPTIONS

-h, --help Print usage statement

--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.

-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

--config="" Specifies the location of the Docker client configuration files. The default is '~/.docker'.

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

-d, --daemon=true|false Enable daemon 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

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

-e, --exec-driver="" Force Docker to use specific exec driver. Default is native.

--exec-opt=[] Set exec driver options. See EXEC DRIVER OPTIONS.

--exec-root="" Path to use as the root of the Docker execdriver. 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.

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

--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".

-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-opt=[] Logging driver specific options.

--mtu=VALUE Set the containers network mtu. Default is 0.

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

--registry-mirror=:// 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 BTRFS storage driver.

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

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

-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.

-v, --version=true|false Print version information and quit. Default is false.

COMMANDS

attach Attach to a running container See docker-attach(1) for full documentation on the attach command.

build Build an image from a Dockerfile See docker-build(1) for full documentation on the build command.

commit Create a new image from a container's changes See docker-commit(1) for full documentation on the commit command.

cp Copy files/folders from a container's filesystem to the host See docker-cp(1) for full documentation on the cp command.

create Create a new container See docker-create(1) for full documentation on the create command.

diff Inspect changes on a container's filesystem See docker-diff(1) for full documentation on the diff command.

events Get real time events from the server See docker-events(1) for full documentation on the events command.

exec Run a command in a running container See docker-exec(1) for full documentation on the exec command.

export Stream the contents of a container as a tar archive See docker-export(1) for full documentation on the export command.

history Show the history of an image See docker-history(1) for full documentation on the history command.

images List images See docker-images(1) for full documentation on the images command.

import Create a new filesystem image from the contents of a tarball See docker-import(1) for full documentation on the import command.

info Display system-wide information See docker-info(1) for full documentation on the info command.

inspect Return low-level information on a container or image See docker-inspect(1) for full documentation on the inspect command.

kill Kill a running container (which includes the wrapper process and everything inside it) See docker-kill(1) for full documentation on the kill command.

load Load an image from a tar archive See docker-load(1) for full documentation on the load command.

login Register or login to a Docker Registry See docker-login(1) for full documentation on the login command.

logout Log the user out of a Docker Registry See docker-logout(1) for full documentation on the logout command.

logs Fetch the logs of a container See docker-logs(1) for full documentation on the logs command.

pause Pause all processes within a container See docker-pause(1) for full documentation on the pause command.

port Lookup the public-facing port which is NAT-ed to PRIVATE_PORT See docker-port(1) for full documentation on the port command.

ps List containers See docker-ps(1) for full documentation on the ps command.

pull Pull an image or a repository from a Docker Registry See docker-pull(1) for full documentation on the pull command.

push Push an image or a repository to a Docker Registry See docker-push(1) for full documentation on the push command.

restart Restart a running container See docker-restart(1) for full documentation on the restart command.

rm Remove one or more containers See docker-rm(1) for full documentation on the rm command.

rmi Remove one or more images See docker-rmi(1) for full documentation on the rmi command.

run Run a command in a new container See docker-run(1) for full documentation on the run command.

save Save an image to a tar archive See docker-save(1) for full documentation on the save command.

search Search for an image in the Docker index See docker-search(1) for full documentation on the search command.

start Start a stopped container See docker-start(1) for full documentation on the start command.

stats Display a live stream of one or more containers' resource usage statistics See docker-stats(1) for full documentation on the stats command.

stop Stop a running container See docker-stop(1) for full documentation on the stop command.

tag Tag an image into a repository See docker-tag(1) for full documentation on the tag command.

top Lookup the running processes of a container See docker-top(1) for full documentation on the top command.

unpause Unpause all processes within a container See docker-unpause(1) for full documentation on the unpause command.

version Show the Docker version information See docker-version(1) for full documentation on the version command.

wait Block until a container stops, then print its exit code See docker-wait(1) for full documentation on the wait command.

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 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:

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 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 -d --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 100G. Note, thin devices are inherently "sparse", so a 100G device which is mostly empty doesn't use 100 GB of space on the pool. However, the filesystem will use more space for base images the larger the device is.

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 -d --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: docker -d --storage-opt dm.fs=xfs

dm.mkfsarg

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

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

dm.mountopt

Specifies extra mount options used when mounting the thin devices.

Example use: docker -d --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: docker -d --storage-opt dm.use_deferred_removal=true

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: docker -d --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 "metadadata" 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 -d --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: docker -d --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: docker -d --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 thedevicemapper and udev during create and cleanup. The race condition results in errors and failures. (For information on these failures, see docker#4036)

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

    $ docker -d --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. Otherwise, set this flag for migrating existing Docker daemons to a daemon with a supported environment.

EXEC DRIVER OPTIONS

Use the --exec-opt flags to specify options to the exec-driver. The only driver that accepts this flag is the native (libcontainer) driver. As a result, you must also specify **-s=**native for this option to have effect. The following is the only native option:

native.cgroupdriver

Specifies the management of the container's cgroups. You can specify cgroupfs or systemd. If you specify systemd and it is not available, the system uses cgroupfs.

Client

For specific client examples please see the man page for the specific Docker command. For example:

man docker-run

HISTORY

April 2014, Originally compiled by William Henry (whenry at redhat dot com) based on docker.com source material and internal work.

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