DockerCLI/docs/reference/commandline/daemon.md

daemon

Usage: docker [OPTIONS] COMMAND [arg...]

A self-sufficient runtime for linux containers.

Options:
  --api-cors-header=""                   Set CORS headers in the remote API
  -b, --bridge=""                        Attach containers to a network bridge
  --bip=""                               Specify network bridge IP
  --config=~/.docker                     Location of client config files
  -D, --debug=false                      Enable debug mode
  -d, --daemon=false                     Enable daemon mode
  --default-gateway=""                   Container default gateway IPv4 address
  --default-gateway-v6=""                Container default gateway IPv6 address
  --dns=[]                               DNS server to use
  --dns-search=[]                        DNS search domains to use
  --default-ulimit=[]                    Set default ulimit settings for containers
  -e, --exec-driver="native"             Exec driver to use
  --exec-opt=[]                          Set exec driver options
  --exec-root="/var/run/docker"          Root of the Docker execdriver
  --fixed-cidr=""                        IPv4 subnet for fixed IPs
  --fixed-cidr-v6=""                     IPv6 subnet for fixed IPs
  -G, --group="docker"                   Group for the unix socket
  -g, --graph="/var/lib/docker"          Root of the Docker runtime
  -H, --host=[]                          Daemon socket(s) to connect to
  -h, --help=false                       Print usage
  --icc=true                             Enable inter-container communication
  --insecure-registry=[]                 Enable insecure registry communication
  --ip=0.0.0.0                           Default IP when binding container ports
  --ip-forward=true                      Enable net.ipv4.ip_forward
  --ip-masq=true                         Enable IP masquerading
  --iptables=true                        Enable addition of iptables rules
  --ipv6=false                           Enable IPv6 networking
  -l, --log-level="info"                 Set the logging level
  --label=[]                             Set key=value labels to the daemon
  --log-driver="json-file"               Default driver for container logs
  --log-opt=[]                           Log driver specific options
  --mtu=0                                Set the containers network MTU
  -p, --pidfile="/var/run/docker.pid"    Path to use for daemon PID file
  --registry-mirror=[]                   Preferred Docker registry mirror
  -s, --storage-driver=""                Storage driver to use
  --selinux-enabled=false                Enable selinux support
  --storage-opt=[]                       Set storage driver options
  --tls=false                            Use TLS; implied by --tlsverify
  --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=false                      Use TLS and verify the remote
  --userland-proxy=true                  Use userland proxy for loopback traffic
  -v, --version=false                    Print version information and quit

Options with [] may be specified multiple times.

The Docker daemon is the persistent process that manages containers. Docker uses the same binary for both the daemon and client. To run the daemon you provide the -d flag.

To run the daemon with debug output, use docker -d -D.

Daemon socket option

The Docker daemon can listen for Docker Remote 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, 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, use docker -d -H fd://. Using fd:// will work perfectly for most setups but you can also specify individual sockets: docker -d -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.

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

# listen using the default unix socket, and on 2 specific IP addresses on this host.
docker -d -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.

$ docker -H tcp://0.0.0.0:2375 ps
# or
$ export DOCKER_HOST="tcp://0.0.0.0:2375"
$ docker ps
# both are equal

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:

$ 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.

Daemon storage-driver option

The Docker daemon has support for several different image layer storage drivers: aufs, devicemapper, btrfs, zfs and overlay.

The aufs driver is the oldest, but is based on a Linux kernel patch-set that is unlikely to be merged into the main kernel. These are also known to cause some serious kernel crashes. However, aufs is also the only storage driver that allows containers to share executable and shared library memory, so is a useful choice when running thousands of containers with the same program or libraries.

The devicemapper driver uses thin provisioning and Copy on Write (CoW) snapshots. For each devicemapper graph location – typically /var/lib/docker/devicemapper – a thin pool is created based on two block devices, one for data and one for metadata. By default, these block devices are created automatically by using loopback mounts of automatically created sparse files. Refer to Storage driver options below for a way how to customize this setup. ~jpetazzo/Resizing Docker containers with the Device Mapper plugin article explains how to tune your existing setup without the use of options.

The btrfs driver is very fast for docker build - but like devicemapper does not share executable memory between devices. Use docker -d -s btrfs -g /mnt/btrfs_partition.

The zfs driver is probably not fast as btrfs but has a longer track record on stability. Thanks to Single Copy ARC shared blocks between clones will be cached only once. Use docker -d -s zfs. To select a different zfs filesystem set zfs.fsname option as described in Storage driver options.

The overlay is a very fast union filesystem. It is now merged in the main Linux kernel as of 3.18.0. Call docker -d -s overlay to use it.

Note: As promising as overlay is, the feature is still quite young and should not be used in production. Most notably, using overlay can cause excessive inode consumption (especially as the number of images grows), as well as being incompatible with the use of RPMs.

Note: It is currently unsupported on btrfs or any Copy on Write filesystem and should only be used over ext4 partitions.

Storage driver options

Particular storage-driver can be configured with options specified with --storage-opt flags. Options for devicemapper are prefixed with dm and options for zfs start with zfs.

• 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 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 the empty case 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.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.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.datadev

  (Deprecated, use dm.thinpooldev)

  Specifies a custom blockdevice to use for data for the thin pool.

  If using a block device for device mapper storage, ideally both datadev and metadatadev should be specified to completely avoid using the loopback device.

  Example use:

  $ docker -d --storage-opt dm.datadev=/dev/sdb1 --storage-opt dm.metadatadev=/dev/sdc1
  

• dm.metadatadev

  (Deprecated, use dm.thinpooldev)

  Specifies a custom blockdevice to use for metadata for the thin pool.

  For best performance the metadata should be on a different spindle than the data, or even better on an SSD.

  If setting up a new metadata pool it is required to be valid. This can be achieved by zeroing the first 4k to indicate empty metadata, like this:

  $ dd if=/dev/zero of=$metadata_dev bs=4096 count=1

  Example use:

  $ docker -d --storage-opt dm.datadev=/dev/sdb1 --storage-opt dm.metadatadev=/dev/sdc1
  

• 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 enabled by default (only) if using loopback devices and is required to resparsify the loopback file on image/container removal.

  Disabling this on loopback can lead to much faster container removal times, but will make the space used in /var/lib/docker directory not be 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

  Overrides the udev synchronization checks between devicemapper and udev. udev is the device manager for the Linux kernel.

  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 udev sync not being supported, set dm.override_udev_sync_check to true:

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

  When this value is true, the devicemapper 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.

Docker execdriver option

Currently supported options of zfs:

• 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:

   $ docker -d -s zfs --storage-opt zfs.fsname=zroot/docker
  

Docker execdriver option

The Docker daemon uses a specifically built libcontainer execution driver as its interface to the Linux kernel namespaces, cgroups, and SELinux.

There is still legacy support for the original LXC userspace tools via the lxc execution driver, however, this is not where the primary development of new functionality is taking place. Add -e lxc to the daemon flags to use the lxc execution driver.

Options for the native execdriver

You can configure the native (libcontainer) execdriver 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 specify cgroupfs or systemd. If you specify systemd and it is not available, the system uses cgroupfs. By default, if no option is specified, the execdriver first tries systemd and falls back to cgroupfs. This example sets the execdriver to cgroupfs:

$ sudo docker -d --exec-opt native.cgroupdriver=cgroupfs

Setting this option applies to all containers the daemon launches.

Daemon DNS options

To set the DNS server for all Docker containers, use docker -d --dns 8.8.8.8.

To set the DNS search domain for all Docker containers, use docker -d --dns-search example.com.

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.

Running a Docker daemon behind a HTTPS_PROXY

When running inside a LAN that uses a 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/ docker -d. 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 builds and running containers will need extra configuration to use the proxy

Default Ulimits

--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 reference.

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:

DOCKER_TMPDIR=/mnt/disk2/tmp /usr/local/bin/docker -d -D -g /var/lib/docker -H unix:// > /var/lib/boot2docker/docker.log 2>&1
# or
export DOCKER_TMPDIR=/mnt/disk2/tmp
/usr/local/bin/docker -d -D -g /var/lib/docker -H unix:// > /var/lib/boot2docker/docker.log 2>&1