DOCKERD(8)

DOCKERD(8) 🌸 — daemon mode, but make it fashion

Welcome to the Docker User Manuals page for dockerd, bestie — section 8, the daemon manual, and we’re gonna read it together because knowledge is the moment 💅.

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✨ NAME ✨

dockerd — Enable daemon mode. That’s the whole name section, short and iconic 🎀.

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🎀 SYNOPSIS 🎀

Okay so here’s the full command shape, copied exactly because flags are sacred:

dockerd [--add-runtime[=[]]] [--allow-nondistributable-artifacts[=[]]]
[--api-cors-header=[=API-CORS-HEADER]] [--authorization-plugin[=[]]]
[-b|--bridge[=BRIDGE]] [--bip[=BIP]] [--cgroup-parent[=[]]] [--config-
file[=path]] [--containerd[=SOCKET-PATH]] [--data-
root[=/var/lib/docker]] [-D|--debug] [--default-cgroupns-mode[=host]]
[--default-gateway[=DEFAULT-GATEWAY]] [--default-gateway-v6[=DEFAULT-
GATEWAY-V6]] [--default-address-pool[=DEFAULT-ADDRESS-POOL]] [--default-
network-opt[=DRIVER=OPT=VALUE]] [--default-runtime[=runc]] [--default-
ipc-mode=MODE] [--default-shm-size[=64MiB]] [--default-ulimit[=[]]]
[--dns[=[]]] [--dns-opt[=[]]] [--dns-search[=[]]] [--exec-opt[=[]]]
[--exec-root[=/var/run/docker]] [--experimental[=false]]
[--feature[=NAME[=true|false]] [--fixed-cidr[=FIXED-CIDR]] [--fixed-
cidr-v6[=FIXED-CIDR-V6]] [-G|--group[=docker]] [-H|--host[=[]]] [--help]
[--http-proxy[""]] [--https-proxy[""]] [--icc[=true]] [--init[=false]]
[--init-path[=""]] [--insecure-registry[=[]]] [--ip[=0.0.0.0]] [--ip-
forward[=true]] [--ip-masq[=true]] [--iptables[=true]] [--ipv6]
[--isolation[=default]] [-l|--log-level[=info]] [--label[=[]]] [--live-
restore[=false]] [--log-driver[=json-file]] [--log-format="text|json"]
[--log-opt[=map[]]] [--mtu[=0]] [--max-concurrent-downloads[=3]] [--max-
concurrent-uploads[=5]] [--max-download-attempts[=5]] [--no-proxy[""]]
[--node-generic-resources[=[]]] [-p|--pidfile[=/var/run/docker.pid]]
[--raw-logs] [--registry-mirror[=[]]] [-s|--storage-driver[=STORAGE-
DRIVER]] [--seccomp-profile[=SECCOMP-PROFILE-PATH]] [--selinux-enabled]
[--shutdown-timeout[=15]] [--storage-opt[=[]]] [--swarm-default-
advertise-addr[=IP|INTERFACE]] [--tls] [--tlscacert[=~/.docker/ca.pem]]
[--tlscert[=~/.docker/cert.pem]] [--tlskey[=~/.docker/key.pem]]
[--tlsverify] [--userland-proxy[=true]] [--userland-proxy-path[""]]
[--userns-remap[=default]] [--validate]

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💖 DESCRIPTION 💖

dockerd is used for starting the Docker daemon (i.e., to command the daemon to manage images, containers etc). So yeah, dockerd is a server, as a daemon — main character energy fr fr 👑.

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]

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🦋 OPTIONS 🦋

Now the options buffet — every flag stays exactly as named, no cap. Vibe check: pass 💅.

• --add-runtime=[] — 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:

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

This is the same example via the command line:

$ 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.

• --allow-nondistributable-artifacts=[] — Push nondistributable artifacts to the specified registries.

List can contain elements with CIDR notation to specify a whole subnet.

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. Lowkey niche, highkey important 🫶.

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.

• --api-cors-header="" — Set CORS headers in the Engine 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.
• --config-file="/etc/docker/daemon.json" — Specifies the JSON file path to load the configuration from. Default is /etc/docker/daemon.json.
• --containerd="" — Path to containerd socket.
• --data-root="" — Path to the directory used to store persisted Docker data such as configuration for resources, swarm cluster state, and filesystem data for images, containers, and local volumes. Default is /var/lib/docker.
• -D, --debug=true|false — Enable debug mode. Default is false.
• --default-cgroupns-mode="host|private" — Set the default cgroup namespace mode for newly created containers. The argument can either be host or private. If unset, this defaults to host on cgroup v1, or private on cgroup v2.
• --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-address-pool="" — Default address pool from which IPAM driver selects a subnet for the networks. Example: base=172.30.0.0/16,size=24 will set the default address pools for the selected scope networks to {172.30.[0-255].0/24}.
• --default-network-opt=DRIVER=OPT=VALUE — Default network driver options.
• --default-runtime="runtime" — Set default runtime if there're more than one specified by --add-runtime.
• --default-ipc-mode="private|shareable" — Set the default IPC mode for newly created containers. The argument can either be private or shareable.
• --default-shm-size=size — Set the daemon-wide default shm size for containers. Default is 64MiB.
• --default-ulimit=[] — Default ulimits for containers.
• --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.
• --experimental="" — Enable the daemon experimental features.
• --feature=NAME[=true|false] — Enable or disable a feature in the daemon. This option corresponds with the "features" field in the daemon.json configuration file. Using both the command-line option and the "features" field in the configuration file produces an error. The feature option can be specified multiple times to configure multiple features. Usage example: --feature containerd-snapshotter or --feature containerd-snapshotter=true.
• --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.
• -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.
• --http-proxy[""] — Proxy URL for HTTP requests unless overridden by NoProxy.
• --https-proxy[""] — Proxy URL for HTTPS requests unless overridden by NoProxy.
• --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.
• --init — Run an init process inside containers for signal forwarding and process reaping.
• --init-path — Path to the docker-init binary.
• --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 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, 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 consult the documentation about "Advanced Networking - IPv6".
• --isolation="default" — sets the isolation tech used by containers 💅 Heads up: the default on Windows server is process, and the default on Windows client is hyperv. Linux only supports default, periodt.
• -l, --log-level="debug|info|warn|error|fatal" — sets the logging level. Default is info. Lowkey iconic for tuning how chatty the daemon is 🎀
• --label="[]" — sets key=value labels on the daemon (shown in docker info) ✨
• --live-restore=false — enables live restore of running containers when the daemon starts, so they are not restarted 🫶 This option is applicable only for a docker daemon running on a Linux host.
• --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. No cap, that warning matters 💀
• --log-format="text|json" — sets the format for logs produced by the daemon. Default is "text" 🌸
• --log-opt=[] — logging driver specific options 🦋
• --mtu=0 — sets the containers network mtu. Default is 0.
• --max-concurrent-downloads=3 — sets the max concurrent downloads. Default is 3 🔥
• --max-concurrent-uploads=5 — sets the max concurrent uploads. Default is 5.
• --max-download-attempts=5 — sets the max download attempts for each pull. Default is 5 👑
• --no-proxy=""" — comma-separated values specifying hosts that should be excluded from proxying 🌈
• --node-generic-resources=[] — advertise user-defined resource. Default is []. Use this if your swarm cluster has some nodes with custom resources (e.g: NVIDIA GPU, SSD, ...) and you need your services to land on nodes advertising these resources. Usage example: --node-generic-resources "NVIDIA-GPU=UUID1" --node-generic-resources "NVIDIA-GPU=UUID2" 💜
• -p, --pidfile="path" — 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=:// — 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.
• --seccomp-profile="" — path to seccomp profile 🦋
• --selinux-enabled=true|false — enable selinux support. Default is false.
• --shutdown-timeout=seconds — set the shutdown timeout value in seconds. Default is 15 ⭐
• --storage-opt=[] — set storage driver options. See STORAGE DRIVER OPTIONS 👀
• --swarm-default-advertise-addr=IP|INTERFACE — set default address or interface for swarm to advertise as its externally-reachable address to other cluster members. This can be a hostname, an IP address, or an interface such as eth0. A port cannot be specified with this option 🫶
• --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 🌸
• --userland-proxy-path="" — path to the userland proxy binary.
• --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 👑
• --validate — validate daemon configuration and exit ✅

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💾 STORAGE DRIVER OPTIONS 💾

Docker uses storage backends (known as "storage drivers" 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 zfs and btrfs. 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 use:

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 use:

docker daemon -s btrfs --storage-opt btrfs.min_space=10G

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🔐 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 🫶

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, see access authorization plugin ⟨https://docs.docker.com/engine/extend/plugins_authorization/⟩ section in the Docker extend section of this documentation 🌈

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⚙️ RUNTIME EXECUTION OPTIONS ⚙️

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:

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

Setting this option applies to all containers the daemon launches 💖

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📜 HISTORY 📜

Sept 2015, Originally compiled by Shishir Mahajan shishir.mahajan@redhat.com ⟨mailto:shishir.mahajan@redhat.com⟩ based on docker.com source material and internal work 🫶

source: Docker Community · version: DOCKERD(8) · date: SEPTEMBER 2015 — later, bestie, go be iconic 💖✨