--- title: "dockerd" description: "The daemon command description and usage" keywords: "container, daemon, runtime" redirect_from: - /engine/reference/commandline/daemon/ --- # daemon ```markdown Usage: dockerd COMMAND A self-sufficient runtime for containers. Options: --add-runtime runtime Register an additional OCI compatible runtime (default []) --allow-nondistributable-artifacts list Allow push of nondistributable artifacts to registry --api-cors-header string Set CORS headers in the Engine API --authorization-plugin list Authorization plugins to load --bip string Specify network bridge IP -b, --bridge string Attach containers to a network bridge --cgroup-parent string Set parent cgroup for all containers --config-file string Daemon configuration file (default "/etc/docker/daemon.json") --containerd string containerd grpc address --containerd-namespace string Containerd namespace to use (default "moby") --containerd-plugins-namespace string Containerd namespace to use for plugins (default "plugins.moby") --cpu-rt-period int Limit the CPU real-time period in microseconds for the parent cgroup for all containers --cpu-rt-runtime int Limit the CPU real-time runtime in microseconds for the parent cgroup for all containers --cri-containerd start containerd with cri --data-root string Root directory of persistent Docker state (default "/var/lib/docker") -D, --debug Enable debug mode --default-address-pool pool-options Default address pools for node specific local networks --default-cgroupns-mode string Default mode for containers cgroup namespace ("host" | "private") (default "host") --default-gateway ip Container default gateway IPv4 address --default-gateway-v6 ip Container default gateway IPv6 address --default-ipc-mode string Default mode for containers ipc ("shareable" | "private") (default "private") --default-runtime string Default OCI runtime for containers (default "runc") --default-shm-size bytes Default shm size for containers (default 64MiB) --default-ulimit ulimit Default ulimits for containers (default []) --dns list DNS server to use --dns-opt list DNS options to use --dns-search list DNS search domains to use --exec-opt list Runtime execution options --exec-root string Root directory for execution state files (default "/var/run/docker") --experimental Enable experimental features --fixed-cidr string IPv4 subnet for fixed IPs --fixed-cidr-v6 string IPv6 subnet for fixed IPs -G, --group string Group for the unix socket (default "docker") --help Print usage -H, --host list Daemon socket(s) to connect to --host-gateway-ip ip IP address that the special 'host-gateway' string in --add-host resolves to. Defaults to the IP address of the default bridge --icc Enable inter-container communication (default true) --init Run an init in the container to forward signals and reap processes --init-path string Path to the docker-init binary --insecure-registry list Enable insecure registry communication --ip ip Default IP when binding container ports (default 0.0.0.0) --ip-forward Enable net.ipv4.ip_forward (default true) --ip-masq Enable IP masquerading (default true) --iptables Enable addition of iptables rules (default true) --ip6tables Enable addition of ip6tables rules (default false) --ipv6 Enable IPv6 networking --label list Set key=value labels to the daemon --live-restore Enable live restore of docker when containers are still running --log-driver string Default driver for container logs (default "json-file") -l, --log-level string Set the logging level ("debug"|"info"|"warn"|"error"|"fatal") (default "info") --log-opt map Default log driver options for containers (default map[]) --max-concurrent-downloads int Set the max concurrent downloads (default 3) --max-concurrent-uploads int Set the max concurrent uploads (default 5) --max-download-attempts int Set the max download attempts for each pull (default 5) --metrics-addr string Set default address and port to serve the metrics api on --mtu int Set the containers network MTU --network-control-plane-mtu int Network Control plane MTU (default 1500) --no-new-privileges Set no-new-privileges by default for new containers --node-generic-resource list Advertise user-defined resource --oom-score-adjust int Set the oom_score_adj for the daemon (default -500) -p, --pidfile string Path to use for daemon PID file (default "/var/run/docker.pid") --raw-logs Full timestamps without ANSI coloring --registry-mirror list Preferred registry mirror --rootless Enable rootless mode; typically used with RootlessKit --seccomp-profile string Path to seccomp profile. Use "unconfined" to disable the default seccomp profile (default "builtin") --selinux-enabled Enable selinux support --shutdown-timeout int Set the default shutdown timeout (default 15) -s, --storage-driver string Storage driver to use --storage-opt list Storage driver options --swarm-default-advertise-addr string Set default address or interface for swarm advertised address --tls Use TLS; implied by --tlsverify --tlscacert string Trust certs signed only by this CA (default "~/.docker/ca.pem") --tlscert string Path to TLS certificate file (default "~/.docker/cert.pem") --tlskey string Path to TLS key file (default "~/.docker/key.pem") --tlsverify Use TLS and verify the remote --userland-proxy Use userland proxy for loopback traffic (default true) --userland-proxy-path string Path to the userland proxy binary --userns-remap string User/Group setting for user namespaces --validate Validate daemon configuration and exit -v, --version Print version information and quit ``` Options with [] may be specified multiple times. ## Description `dockerd` is the persistent process that manages containers. Docker uses different binaries for the daemon and client. To run the daemon you type `dockerd`. To run the daemon with debug output, use `dockerd --debug` or add `"debug": true` to [the `daemon.json` file](#daemon-configuration-file). > **Enabling experimental features** > > Enable experimental features by starting `dockerd` with the `--experimental` > flag or adding `"experimental": true` to the `daemon.json` file. ### Environment variables For easy reference, the following list of environment variables are supported by the `dockerd` command line: | Variable | Description | |:--------------------|:----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| | `DOCKER_CERT_PATH` | Location of your authentication keys. This variable is used both by the [`docker` CLI](cli.md) and the `dockerd` daemon. | | `DOCKER_DRIVER` | The storage driver to use. | | `DOCKER_RAMDISK` | If set this disables 'pivot_root'. | | `DOCKER_TLS_VERIFY` | When set Docker uses TLS and verifies the remote. This variable is used both by the [`docker` CLI](cli.md) and the `dockerd` daemon. | | `DOCKER_TMPDIR` | Location for temporary files created by the daemon. | | `HTTP_PROXY` | Proxy URL for HTTP requests unless overridden by NoProxy. See the [Go specification](https://pkg.go.dev/golang.org/x/net/http/httpproxy#Config) for details. | | `HTTPS_PROXY` | Proxy URL for HTTPS requests unless overridden by NoProxy. See the [Go specification](https://pkg.go.dev/golang.org/x/net/http/httpproxy#Config) for details. | | `MOBY_DISABLE_PIGZ` | Disables the use of [`unpigz`](https://linux.die.net/man/1/pigz) to decompress layers in parallel when pulling images, even if it is installed. | | | `NO_PROXY` | Comma-separated values specifying hosts that should be excluded from proxying. See the [Go specification](https://pkg.go.dev/golang.org/x/net/http/httpproxy#Config) for details. | ## Examples ### Daemon socket option The Docker daemon can listen for [Docker Engine API](https://docs.docker.com/engine/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](https://docs.docker.com/engine/security/https/), 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](https://0pointer.de/blog/projects/socket-activation.html), use `dockerd -H fd://`. Using `fd://` will work perfectly for most setups but you can also specify individual sockets: `dockerd -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](https://github.com/docker/docker/tree/master/contrib/init/systemd/). You can configure the Docker daemon to listen to multiple sockets at the same time using multiple `-H` options: The example below runs the daemon listenin on the default unix socket, and on 2 specific IP addresses on this host: ```console $ sudo dockerd -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. Use **one** of the following commands: ```console $ docker -H tcp://0.0.0.0:2375 ps ``` ```console $ export DOCKER_HOST="tcp://0.0.0.0:2375" $ docker ps ``` 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: ```console $ 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`. The Docker client supports connecting to a remote daemon via SSH: ```console $ docker -H ssh://me@example.com:22 ps $ docker -H ssh://me@example.com ps $ docker -H ssh://example.com ps ``` To use SSH connection, you need to set up `ssh` so that it can reach the remote host with public key authentication. Password authentication is not supported. If your key is protected with passphrase, you need to set up `ssh-agent`. #### Bind Docker to another host/port or a Unix socket > **Warning** > > Changing the default `docker` daemon binding to a > TCP port or Unix *docker* user group will increase your security risks > by allowing non-root users to gain *root* access on the host. Make sure > you control access to `docker`. If you are binding > to a TCP port, anyone with access to that port has full Docker access; > so it is not advisable on an open network. {: .warning :} With `-H` it is possible to make the Docker daemon to listen on a specific IP and port. By default, it will listen on `unix:///var/run/docker.sock` to allow only local connections by the *root* user. You *could* set it to `0.0.0.0:2375` or a specific host IP to give access to everybody, but that is **not recommended** because then it is trivial for someone to gain root access to the host where the daemon is running. Similarly, the Docker client can use `-H` to connect to a custom port. The Docker client will default to connecting to `unix:///var/run/docker.sock` on Linux, and `tcp://127.0.0.1:2376` on Windows. `-H` accepts host and port assignment in the following format: tcp://[host]:[port][path] or unix://path For example: - `tcp://` -> TCP connection to `127.0.0.1` on either port `2376` when TLS encryption is on, or port `2375` when communication is in plain text. - `tcp://host:2375` -> TCP connection on host:2375 - `tcp://host:2375/path` -> TCP connection on host:2375 and prepend path to all requests - `unix://path/to/socket` -> Unix socket located at `path/to/socket` `-H`, when empty, will default to the same value as when no `-H` was passed in. `-H` also accepts short form for TCP bindings: `host:` or `host:port` or `:port` Run Docker in daemon mode: ```console $ sudo /dockerd -H 0.0.0.0:5555 & ``` Download an `ubuntu` image: ```console $ docker -H :5555 pull ubuntu ``` You can use multiple `-H`, for example, if you want to listen on both TCP and a Unix socket ```console $ sudo dockerd -H tcp://127.0.0.1:2375 -H unix:///var/run/docker.sock & # Download an ubuntu image, use default Unix socket $ docker pull ubuntu # OR use the TCP port $ docker -H tcp://127.0.0.1:2375 pull ubuntu ``` ### Daemon storage-driver On Linux, the Docker daemon has support for several different image layer storage drivers: `aufs`, `devicemapper`, `btrfs`, `zfs`, `overlay`, `overlay2`, and `fuse-overlayfs`. `overlay2` is the preferred storage driver for all currently supported Linux distributions, and is selected by default. Unless users have a strong reason to prefer another storage driver, `overlay2` should be used. You can find out more about storage drivers and how to select one in [Select a storage driver](https://docs.docker.com/storage/storagedriver/select-storage-driver/). On Windows, the Docker daemon only supports the `windowsfilter` storage driver. ### Options per storage driver Particular storage-driver can be configured with options specified with `--storage-opt` flags. Options for `devicemapper` are prefixed with `dm`, options for `zfs` start with `zfs`, and options for `btrfs` start with `btrfs`. #### Devicemapper options This is an example of the configuration file for devicemapper on Linux: ```json { "storage-driver": "devicemapper", "storage-opts": [ "dm.thinpooldev=/dev/mapper/thin-pool", "dm.use_deferred_deletion=true", "dm.use_deferred_removal=true" ] } ``` ##### `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: ```console $ sudo dockerd --storage-opt dm.thinpooldev=/dev/mapper/thin-pool ``` ##### `dm.directlvm_device` As an alternative to providing a thin pool as above, Docker can setup a block device for you. ###### Example: ```console $ sudo dockerd --storage-opt dm.directlvm_device=/dev/xvdf ``` ##### `dm.thinp_percent` Sets the percentage of passed in block device to use for storage. ###### Example: ```console $ sudo dockerd --storage-opt dm.thinp_percent=95 ``` ##### `dm.thinp_metapercent` Sets the percentage of the passed in block device to use for metadata storage. ###### Example: ```console $ sudo dockerd --storage-opt dm.thinp_metapercent=1 ``` ##### `dm.thinp_autoextend_threshold` Sets the value of the percentage of space used before `lvm` attempts to autoextend the available space [100 = disabled] ###### Example: ```console $ sudo dockerd --storage-opt dm.thinp_autoextend_threshold=80 ``` ##### `dm.thinp_autoextend_percent` Sets the value percentage value to increase the thin pool by when `lvm` attempts to autoextend the available space [100 = disabled] ###### Example: ```console $ sudo dockerd --storage-opt dm.thinp_autoextend_percent=20 ``` ##### `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 the empty case 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. ###### Examples ```console $ sudo 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: ```console $ sudo service docker stop $ sudo rm -rf /var/lib/docker $ sudo service docker start ``` ##### `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 ```console $ sudo 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 ```console $ sudo dockerd --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 "xfs" ###### Example ```console $ sudo dockerd --storage-opt dm.fs=ext4 ``` ##### `dm.mkfsarg` Specifies extra mkfs arguments to be used when creating the base device. ###### Example ```console $ sudo dockerd --storage-opt "dm.mkfsarg=-O ^has_journal" ``` ##### `dm.mountopt` Specifies extra mount options used when mounting the thin devices. ###### Example ```console $ sudo dockerd --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 ```console $ sudo dockerd \ --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: ```console $ dd if=/dev/zero of=$metadata_dev bs=4096 count=1 ``` ###### Example ```console $ sudo dockerd \ --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 ```console $ sudo dockerd --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. ###### Examples ```console $ sudo dockerd --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: ```console $ 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 `udev` sync not being supported, set `dm.override_udev_sync_check` to true: ```console $ sudo dockerd --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](https://github.com/docker/docker/issues/4036). > Otherwise, set this flag for migrating existing Docker daemons to > a daemon with a supported environment. ##### `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 ```console $ sudo 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. ```console 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. ```console $ sudo 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.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 sufficient 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 the thin pool. You can also add more storage to the thin pool. To add more space to a LVM (logical volume management) thin pool, just add more storage to the volume 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 ```console $ sudo dockerd --storage-opt dm.min_free_space=10% ``` ##### `dm.xfs_nospace_max_retries` Specifies the maximum number of retries XFS should attempt to complete IO when ENOSPC (no space) error is returned by underlying storage device. By default XFS retries infinitely for IO to finish and this can result in unkillable process. To change this behavior one can set xfs_nospace_max_retries to say 0 and XFS will not retry IO after getting ENOSPC and will shutdown filesystem. ###### Example ```console $ sudo dockerd --storage-opt dm.xfs_nospace_max_retries=0 ``` ##### `dm.libdm_log_level` Specifies the maxmimum `libdm` log level that will be forwarded to the `dockerd` log (as specified by `--log-level`). This option is primarily intended for debugging problems involving `libdm`. Using values other than the defaults may cause false-positive warnings to be logged. Values specified must fall within the range of valid `libdm` log levels. At the time of writing, the following is the list of `libdm` log levels as well as their corresponding levels when output by `dockerd`. | `libdm` Level | Value | `--log-level` | |---------------|------:|---------------| | `_LOG_FATAL` | 2 | error | | `_LOG_ERR` | 3 | error | | `_LOG_WARN` | 4 | warn | | `_LOG_NOTICE` | 5 | info | | `_LOG_INFO` | 6 | info | | `_LOG_DEBUG` | 7 | debug | ###### Example ```console $ sudo dockerd \ --log-level debug \ --storage-opt dm.libdm_log_level=7 ``` #### 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 ```console $ sudo 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 ```console $ sudo dockerd -s btrfs --storage-opt btrfs.min_space=10G ``` #### Overlay2 options ##### `overlay2.size` Sets the default max size of the container. It is supported only when the backing fs is `xfs` and mounted with `pquota` mount option. Under these conditions the user can pass any size less than the backing fs size. ###### Example ```console $ sudo dockerd -s overlay2 --storage-opt overlay2.size=1G ``` #### Windowsfilter options ##### `size` Specifies the size to use when creating the sandbox which is used for containers. Defaults to 20G. ###### Example ```powershell C:\> dockerd --storage-opt size=40G ``` ### Docker runtime execution options The Docker daemon relies on a [OCI](https://github.com/opencontainers/runtime-spec) compliant runtime (invoked via the `containerd` daemon) as its interface to the Linux kernel `namespaces`, `cgroups`, and `SELinux`. By default, the Docker daemon automatically starts `containerd`. If you want to control `containerd` startup, manually start `containerd` and pass the path to the `containerd` socket using the `--containerd` flag. For example: ```console $ sudo dockerd --containerd /var/run/dev/docker-containerd.sock ``` 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: ```json { "default-runtime": "runc", "runtimes": { "custom": { "path": "/usr/local/bin/my-runc-replacement", "runtimeArgs": [ "--debug" ] }, "runc": { "path": "runc" } } } ``` This is the same example via the command line: ```console $ 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. #### Options for the runtime 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`: ```console $ sudo dockerd --exec-opt native.cgroupdriver=systemd ``` Setting this option applies to all containers the daemon launches. Also Windows Container makes use of `--exec-opt` for special purpose. Docker user can specify default container isolation technology with this, for example: ```console > dockerd --exec-opt isolation=hyperv ``` Will make `hyperv` the default isolation technology on Windows. If no isolation value is specified on daemon start, on Windows client, the default is `hyperv`, and on Windows server, the default is `process`. ### Daemon DNS options To set the DNS server for all Docker containers, use: ```console $ sudo dockerd --dns 8.8.8.8 ``` To set the DNS search domain for all Docker containers, use: ```console $ sudo dockerd --dns-search example.com ``` ### Allow push of nondistributable artifacts Some images (e.g., Windows base images) contain artifacts whose distribution is restricted by license. When these images are pushed to a registry, restricted artifacts are not included. To override this behavior for specific registries, use the `--allow-nondistributable-artifacts` option in one of the following forms: * `--allow-nondistributable-artifacts myregistry:5000` tells the Docker daemon to push nondistributable artifacts to myregistry:5000. * `--allow-nondistributable-artifacts 10.1.0.0/16` tells the Docker daemon to push nondistributable artifacts to all registries whose resolved IP address is within the subnet described by the CIDR syntax. This option can be used multiple times. 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. > **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. ### 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. Enabling `--insecure-registry`, i.e., allowing un-encrypted and/or untrusted communication, can be 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 enabling `--insecure-registry`. #### Legacy Registries Operations against registries supporting only the legacy v1 protocol are no longer supported. Specifically, the daemon will not attempt `push`, `pull` and `login` to v1 registries. The exception to this is `search` which can still be performed on v1 registries. ### Running a Docker daemon behind an HTTPS_PROXY When running inside a LAN that uses an `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/ dockerd`. 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 build`s and running containers will need extra configuration to use the proxy ### Default `ulimit` settings `--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](run.md) reference. ### 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. ```console $ sudo 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, refer to the [authorization plugin](../../extend/plugins_authorization.md) section. ### Daemon user namespace options The Linux kernel [user namespace support](https://man7.org/linux/man-pages/man7/user_namespaces.7.html) provides additional security by enabling a process, and therefore a container, to have a unique range of user and group IDs which are outside the traditional user and group range utilized by the host system. Potentially the most important security improvement is that, by default, container processes running as the `root` user will have expected administrative privilege (with some restrictions) inside the container but will effectively be mapped to an unprivileged `uid` on the host. For details about how to use this feature, as well as limitations, see [Isolate containers with a user namespace](https://docs.docker.com/engine/security/userns-remap/). ### 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: ```console $ DOCKER_TMPDIR=/mnt/disk2/tmp /usr/local/bin/dockerd --data-root /var/lib/docker -H unix:// > /var/lib/docker-machine/docker.log 2>&1 ``` or ```console $ export DOCKER_TMPDIR=/mnt/disk2/tmp $ /usr/local/bin/dockerd --data-root /var/lib/docker -H unix:// > /var/lib/docker-machine/docker.log 2>&1 ```` #### Default cgroup parent The `--cgroup-parent` option allows you to set the default cgroup parent to use for containers. If this option is not set, it defaults to `/docker` for fs cgroup driver and `system.slice` for systemd cgroup driver. If the cgroup has a leading forward slash (`/`), the cgroup is created under the root cgroup, otherwise the cgroup is created under the daemon cgroup. Assuming the daemon is running in cgroup `daemoncgroup`, `--cgroup-parent=/foobar` creates a cgroup in `/sys/fs/cgroup/memory/foobar`, whereas using `--cgroup-parent=foobar` creates the cgroup in `/sys/fs/cgroup/memory/daemoncgroup/foobar` The systemd cgroup driver has different rules for `--cgroup-parent`. Systemd represents hierarchy by slice and the name of the slice encodes the location in the tree. So `--cgroup-parent` for systemd cgroups should be a slice name. A name can consist of a dash-separated series of names, which describes the path to the slice from the root slice. For example, `--cgroup-parent=user-a-b.slice` means the memory cgroup for the container is created in `/sys/fs/cgroup/memory/user.slice/user-a.slice/user-a-b.slice/docker-.scope`. This setting can also be set per container, using the `--cgroup-parent` option on `docker create` and `docker run`, and takes precedence over the `--cgroup-parent` option on the daemon. #### Daemon metrics The `--metrics-addr` option takes a tcp address to serve the metrics API. This feature is still experimental, therefore, the daemon must be running in experimental mode for this feature to work. To serve the metrics API on `localhost:9323` you would specify `--metrics-addr 127.0.0.1:9323`, allowing you to make requests on the API at `127.0.0.1:9323/metrics` to receive metrics in the [prometheus](https://prometheus.io/docs/instrumenting/exposition_formats/) format. Port `9323` is the [default port associated with Docker metrics](https://github.com/prometheus/prometheus/wiki/Default-port-allocations) to avoid collisions with other prometheus exporters and services. If you are running a prometheus server you can add this address to your scrape configs to have prometheus collect metrics on Docker. For more information on prometheus refer to the [prometheus website](https://prometheus.io/). ```yaml scrape_configs: - job_name: 'docker' static_configs: - targets: ['127.0.0.1:9323'] ``` Please note that this feature is still marked as experimental as metrics and metric names could change while this feature is still in experimental. Please provide feedback on what you would like to see collected in the API. #### Node Generic Resources The `--node-generic-resources` option takes a list of key-value pair (`key=value`) that allows you to advertise user defined resources in a swarm cluster. The current expected use case is to advertise NVIDIA GPUs so that services requesting `NVIDIA-GPU=[0-16]` can land on a node that has enough GPUs for the task to run. Example of usage: ```json { "node-generic-resources": [ "NVIDIA-GPU=UUID1", "NVIDIA-GPU=UUID2" ] } ``` ### Daemon configuration file The `--config-file` option allows you to set any configuration option for the daemon in a JSON format. This file uses the same flag names as keys, except for flags that allow several entries, where it uses the plural of the flag name, e.g., `labels` for the `label` flag. The options set in the configuration file must not conflict with options set via flags. The docker daemon fails to start if an option is duplicated between the file and the flags, regardless of their value. We do this to avoid silently ignore changes introduced in configuration reloads. For example, the daemon fails to start if you set daemon labels in the configuration file and also set daemon labels via the `--label` flag. Options that are not present in the file are ignored when the daemon starts. The `--validate` option allows to validate a configuration file without starting the Docker daemon. A non-zero exit code is returned for invalid configuration files. ```console $ dockerd --validate --config-file=/tmp/valid-config.json configuration OK $ echo $? 0 $ dockerd --validate --config-file /tmp/invalid-config.json unable to configure the Docker daemon with file /tmp/invalid-config.json: the following directives don't match any configuration option: unknown-option $ echo $? 1 ``` ##### On Linux The default location of the configuration file on Linux is `/etc/docker/daemon.json`. The `--config-file` flag can be used to specify a non-default location. This is a full example of the allowed configuration options on Linux: ```json { "allow-nondistributable-artifacts": [], "api-cors-header": "", "authorization-plugins": [], "bip": "", "bridge": "", "cgroup-parent": "", "containerd": "/run/containerd/containerd.sock", "containerd-namespace": "docker", "containerd-plugin-namespace": "docker-plugins", "data-root": "", "debug": true, "default-address-pools": [ { "base": "172.30.0.0/16", "size": 24 }, { "base": "172.31.0.0/16", "size": 24 } ], "default-cgroupns-mode": "private", "default-gateway": "", "default-gateway-v6": "", "default-runtime": "runc", "default-shm-size": "64M", "default-ulimits": { "nofile": { "Hard": 64000, "Name": "nofile", "Soft": 64000 } }, "dns": [], "dns-opts": [], "dns-search": [], "exec-opts": [], "exec-root": "", "experimental": false, "features": {}, "fixed-cidr": "", "fixed-cidr-v6": "", "group": "", "hosts": [], "icc": false, "init": false, "init-path": "/usr/libexec/docker-init", "insecure-registries": [], "ip": "0.0.0.0", "ip-forward": false, "ip-masq": false, "iptables": false, "ip6tables": false, "ipv6": false, "labels": [], "live-restore": true, "log-driver": "json-file", "log-level": "", "log-opts": { "cache-disabled": "false", "cache-max-file": "5", "cache-max-size": "20m", "cache-compress": "true", "env": "os,customer", "labels": "somelabel", "max-file": "5", "max-size": "10m" }, "max-concurrent-downloads": 3, "max-concurrent-uploads": 5, "max-download-attempts": 5, "mtu": 0, "no-new-privileges": false, "node-generic-resources": [ "NVIDIA-GPU=UUID1", "NVIDIA-GPU=UUID2" ], "oom-score-adjust": -500, "pidfile": "", "raw-logs": false, "registry-mirrors": [], "runtimes": { "cc-runtime": { "path": "/usr/bin/cc-runtime" }, "custom": { "path": "/usr/local/bin/my-runc-replacement", "runtimeArgs": [ "--debug" ] } }, "seccomp-profile": "", "selinux-enabled": false, "shutdown-timeout": 15, "storage-driver": "", "storage-opts": [], "swarm-default-advertise-addr": "", "tls": true, "tlscacert": "", "tlscert": "", "tlskey": "", "tlsverify": true, "userland-proxy": false, "userland-proxy-path": "/usr/libexec/docker-proxy", "userns-remap": "" } ``` > **Note:** > > You cannot set options in `daemon.json` that have already been set on > daemon startup as a flag. > On systems that use `systemd` to start the Docker daemon, `-H` is already set, so > you cannot use the `hosts` key in `daemon.json` to add listening addresses. > See ["custom Docker daemon options"](https://docs.docker.com/config/daemon/systemd/#custom-docker-daemon-options) for how > to accomplish this task with a systemd drop-in file. ##### On Windows The default location of the configuration file on Windows is `%programdata%\docker\config\daemon.json`. The `--config-file` flag can be used to specify a non-default location. This is a full example of the allowed configuration options on Windows: ```json { "allow-nondistributable-artifacts": [], "authorization-plugins": [], "bridge": "", "containerd": "\\\\.\\pipe\\containerd-containerd", "containerd-namespace": "docker", "containerd-plugin-namespace": "docker-plugins", "data-root": "", "debug": true, "default-runtime": "", "default-ulimits": {}, "dns": [], "dns-opts": [], "dns-search": [], "exec-opts": [], "experimental": false, "features": {}, "fixed-cidr": "", "group": "", "hosts": [], "insecure-registries": [], "labels": [], "log-driver": "", "log-level": "", "max-concurrent-downloads": 3, "max-concurrent-uploads": 5, "max-download-attempts": 5, "mtu": 0, "pidfile": "", "raw-logs": false, "registry-mirrors": [], "shutdown-timeout": 15, "storage-driver": "", "storage-opts": [], "swarm-default-advertise-addr": "", "tlscacert": "", "tlscert": "", "tlskey": "", "tlsverify": true } ``` The `default-runtime` option is by default unset, in which case dockerd will auto-detect the runtime. This detection is currently based on if the `containerd` flag is set. Accepted values: - `com.docker.hcsshim.v1` - This is the built-in runtime that Docker has used since Windows supported was first added and uses the v1 HCS API's in Windows. - `io.containerd.runhcs.v1` - This is uses the containerd `runhcs` shim to run the container and uses the v2 HCS API's in Windows. #### Feature options The optional field `features` in `daemon.json` allows users to enable or disable specific daemon features. For example, `{"features":{"buildkit": true}}` enables `buildkit` as the default docker image builder. The list of currently supported feature options: - `buildkit`: It enables `buildkit` as default builder when set to `true` or disables it by `false`. Note that if this option is not explicitly set in the daemon config file, then it is up to the cli to determine which builder to invoke. #### Configuration reload behavior Some options can be reconfigured when the daemon is running without requiring to restart the process. We use the `SIGHUP` signal in Linux to reload, and a global event in Windows with the key `Global\docker-daemon-config-$PID`. The options can be modified in the configuration file but still will check for conflicts with the provided flags. The daemon fails to reconfigure itself if there are conflicts, but it won't stop execution. The list of currently supported options that can be reconfigured is this: - `debug`: it changes the daemon to debug mode when set to true. - `labels`: it replaces the daemon labels with a new set of labels. - `live-restore`: Enables [keeping containers alive during daemon downtime](https://docs.docker.com/config/containers/live-restore/). - `max-concurrent-downloads`: it updates the max concurrent downloads for each pull. - `max-concurrent-uploads`: it updates the max concurrent uploads for each push. - `max-download-attempts`: it updates the max download attempts for each pull. - `default-runtime`: it updates the runtime to be used if not is specified at container creation. It defaults to "default" which is the runtime shipped with the official docker packages. - `runtimes`: it updates the list of available OCI runtimes that can be used to run containers. - `authorization-plugin`: it specifies the authorization plugins to use. - `allow-nondistributable-artifacts`: Replaces the set of registries to which the daemon will push nondistributable artifacts with a new set of registries. - `insecure-registries`: it replaces the daemon insecure registries with a new set of insecure registries. If some existing insecure registries in daemon's configuration are not in newly reloaded insecure registries, these existing ones will be removed from daemon's config. - `registry-mirrors`: it replaces the daemon registry mirrors with a new set of registry mirrors. If some existing registry mirrors in daemon's configuration are not in newly reloaded registry mirrors, these existing ones will be removed from daemon's config. - `shutdown-timeout`: it replaces the daemon's existing configuration timeout with a new timeout for shutting down all containers. - `features`: it explicitly enables or disables specific features. ### Run multiple daemons > **Note:** > > Running multiple daemons on a single host is considered as "experimental". The user should be aware of > unsolved problems. This solution may not work properly in some cases. Solutions are currently under development > and will be delivered in the near future. This section describes how to run multiple Docker daemons on a single host. To run multiple daemons, you must configure each daemon so that it does not conflict with other daemons on the same host. You can set these options either by providing them as flags, or by using a [daemon configuration file](#daemon-configuration-file). The following daemon options must be configured for each daemon: ```console -b, --bridge= Attach containers to a network bridge --exec-root=/var/run/docker Root of the Docker execdriver --data-root=/var/lib/docker Root of persisted Docker data -p, --pidfile=/var/run/docker.pid Path to use for daemon PID file -H, --host=[] Daemon socket(s) to connect to --iptables=true Enable addition of iptables rules --config-file=/etc/docker/daemon.json Daemon configuration file --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 ``` When your daemons use different values for these flags, you can run them on the same host without any problems. It is very important to properly understand the meaning of those options and to use them correctly. - The `-b, --bridge=` flag is set to `docker0` as default bridge network. It is created automatically when you install Docker. If you are not using the default, you must create and configure the bridge manually or just set it to 'none': `--bridge=none` - `--exec-root` is the path where the container state is stored. The default value is `/var/run/docker`. Specify the path for your running daemon here. - `--data-root` is the path where persisted data such as images, volumes, and cluster state are stored. The default value is `/var/lib/docker`. To avoid any conflict with other daemons, set this parameter separately for each daemon. - `-p, --pidfile=/var/run/docker.pid` is the path where the process ID of the daemon is stored. Specify the path for your pid file here. - `--host=[]` specifies where the Docker daemon will listen for client connections. If unspecified, it defaults to `/var/run/docker.sock`. - `--iptables=false` prevents the Docker daemon from adding iptables rules. If multiple daemons manage iptables rules, they may overwrite rules set by another daemon. Be aware that disabling this option requires you to manually add iptables rules to expose container ports. If you prevent Docker from adding iptables rules, Docker will also not add IP masquerading rules, even if you set `--ip-masq` to `true`. Without IP masquerading rules, Docker containers will not be able to connect to external hosts or the internet when using network other than default bridge. - `--config-file=/etc/docker/daemon.json` is the path where configuration file is stored. You can use it instead of daemon flags. Specify the path for each daemon. - `--tls*` Docker daemon supports `--tlsverify` mode that enforces encrypted and authenticated remote connections. The `--tls*` options enable use of specific certificates for individual daemons. Example script for a separate “bootstrap” instance of the Docker daemon without network: ```console $ sudo dockerd \ -H unix:///var/run/docker-bootstrap.sock \ -p /var/run/docker-bootstrap.pid \ --iptables=false \ --ip-masq=false \ --bridge=none \ --data-root=/var/lib/docker-bootstrap \ --exec-root=/var/run/docker-bootstrap ```