Usage: dockerd [OPTIONS]
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
--cdi-spec-dir list CDI specification directories to use
--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 (not supported with cgroups v2)
--cpu-rt-runtime int Limit the CPU real-time runtime in microseconds for the
parent cgroup for all containers (not supported with cgroups v2)
--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 "private")
--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-network-opt mapmap Default network options (default map[])
--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
--feature map Enable feature in the daemon
--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
--http-proxy string HTTP proxy URL to use for outgoing traffic
--https-proxy string HTTPS proxy URL to use for outgoing traffic
--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)
--ip6tables Enable addition of ip6tables rules (experimental)
--iptables Enable addition of iptables rules (default true)
--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")
--log-format string Set the logging format ("text"|"json") (default "text")
-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 (default 1500)
--network-control-plane-mtu int Network Control plane MTU (default 1500)
--no-new-privileges Set no-new-privileges by default for new containers
--no-proxy string Comma-separated list of hosts or IP addresses for which the proxy is skipped
--node-generic-resource list Advertise user-defined resource
--oom-score-adjust int Set the oom_score_adj for the daemon
-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
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.
Note
Enabling experimental features
Enable experimental features by starting dockerd with the --experimental
flag or adding "experimental": true to the daemon.json file.
The following list of environment variables are supported by the dockerd daemon.
Some of these environment variables are supported both by the Docker Daemon and
the docker CLI. Refer to
Environment variables
to learn about environment variables supported by the docker CLI.
Variable
Description
DOCKER_CERT_PATH
Location of your authentication keys. This variable is used both by the
docker CLI 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 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 for details.
HTTPS_PROXY
Proxy URL for HTTPS requests unless overridden by NoProxy. See the
Go specification for details.
MOBY_DISABLE_PIGZ
Disables the use of
unpigz 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 for details.
If you are behind an HTTP proxy server, for example in corporate settings,
you may have to configure the Docker daemon to use the proxy server for
operations such as pulling and pushing images. The daemon can be configured
in three ways:
Using environment variables (HTTP_PROXY, HTTPS_PROXY, and NO_PROXY).
Using the http-proxy, https-proxy, and no-proxy fields in the
daemon configuration file (Docker Engine version 23.0 or later).
Using the --http-proxy, --https-proxy, and --no-proxy command-line
options. (Docker Engine version 23.0 or later).
The command-line and configuration file options take precedence over environment
variables. Refer to
control and configure Docker with systemd
to set these environment variables on a host using systemd.
The Docker daemon can listen for
Docker 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.
Note What is /var/run/docker.sock?
/var/run/docker.sock is the default Unix socket. Sockets are meant for communication between processes on the same
host.
Docker daemon by default listens to docker.sock. If Docker client and daemon are running on the same host, we
can the /var/run/docker.sock to manage containers, which means we can mount the Docker socket from the host into
the container.
For example, if we run the following command, it will return the version of the docker engine.
Things get little trickier when we run docker inside docker, in which case we have to run docker with the default
Unix socket docker.sock as a volume. For example
docker run -v /var/run/docker.sock:/var/run/docker.sock -it docker
From within the container A, we should be able to execute docker commands for building and pushing images to the
registry.
Here, the actual docker operations in A happen on the VM host running our base docker container rather than from
within the container A. Although container A has access to the Docker socket and is able to start container B, A
is starting B as "sibling" container instead of "child" container. The setup looks like Docker-in-Docker, feels like
Docker-in-Docker, but it's not Docker-in-Docker: when this container A will create more containers, those containers
will be created in the top-level Docker. We will not experience nesting side effects, and the build cache will be
shared across multiple invocations. Hence the correct mental model shall look like this:
Just a word of caution: If a container gets access to docker.sock, it means it has more privileges over docker
daemon. So when used in real projects, understand the security risks, and use it.
If you need to access the Docker daemon remotely, you need to enable the tcp
Socket. When using a TCP socket, the Docker daemon provides un-encrypted and
un-authenticated direct access to the Docker daemon by default. You should secure
the daemon 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
TLS version 1.0 and higher is supported. Protocols SSLv3 and below are not
supported for security reasons.
On systemd based systems, you can communicate with the daemon via
systemd socket activation,
with dockerd -H fd://. Using fd:// works for most setups, but
you can also specify individual sockets: dockerd -H fd://3. If the
specified socket activated files aren't found, the daemon exits. 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:
The example below runs the daemon listening on the default Unix socket, and
on 2 specific IP addresses on this host:
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
$exportDOCKER_TLS_VERIFY=1$ docker ps
The Docker client honors 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:
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.
Changing the default docker daemon binding to a TCP port or Unix docker
user group introduces security risks, as it may allow 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's not advisable on an open network.
With -H it's possible to make the Docker daemon to listen on a specific IP
and port. By default, it listens 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 isn't recommended
because someone could 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 defaults 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, defaults 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:
$ sudo <path to>/dockerd -H 0.0.0.0:5555 &
Download an ubuntu image:
$ docker -H :5555 pull ubuntu
You can use multiple -H, for example, if you want to listen on both
TCP and a Unix socket
$ 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
On Linux, the Docker daemon has support for several different image layer storage
drivers: overlay2, fuse-overlayfs, btrfs, and zfs.
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.
On Windows, the Docker daemon only supports the windowsfilter storage driver.
Particular storage-driver can be configured with options specified with
--storage-opt flags. Options for zfs start with zfs, and options for
btrfs start with btrfs.
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 can't be smaller than btrfs.min_space.
Sets the default max size of the container. It is supported only when the
backing filesystem is xfs and mounted with pquota mount option. Under these
conditions the user can pass any size less than the backing filesystem size.
The Docker daemon relies on a
OCI compliant runtime
(invoked via the containerd daemon) as its interface to the Linux
kernel namespaces, cgroups, and SELinux.
By default, the Docker daemon uses runc as a container runtime.
You can configure the daemon to add additional runtimes.
containerd shims installed on PATH can be used directly, without the need
to edit the daemon's configuration. For example, if you install the Kata
Containers shim (containerd-shim-kata-v2) on PATH, then you can select that
runtime with docker run without having to edit the daemon's configuration:
$ docker run --runtime io.containerd.kata.v2
Container runtimes that don't implement containerd shims, or containerd shims
installed outside of PATH, must be registered with the daemon, either via the
configuration file or using the --add-runtime command line flag.
To register and configure container runtimes using the daemon's configuration
file, add the runtimes as entries under runtimes:
{"runtimes":{"<runtime>":{}}}
The key of the entry (<runtime> in the previous example) represents the name
of the runtime. This is the name that you reference when you run a container,
using docker run --runtime <runtime>.
The runtime entry contains an object specifying the configuration for your
runtime. The properties of the object depends on what kind of runtime you're
looking to register:
If the runtime implements its own containerd shim, the object shall contain
a runtimeType field and an optional options field.
If the runtime that you want to register implements a containerd shim,
or if you want to register a runtime which uses the runc shim,
use the following format for the runtime entry:
The fully qualified name of a shim is the same as the runtime_type used to
register the runtime in containerd's CRI configuration.
For example, io.containerd.runsc.v1.
The path of a containerd shim binary.
This option is useful if you installed the containerd shim binary outside of
PATH.
options is optional. It lets you specify the runtime configuration that you
want to use for the shim. The configuration parameters that you can specify in
options depends on the runtime you're registering. For most shims,
the supported configuration options are TypeUrl and ConfigPath.
For example:
The options field takes a special set of configuration parameters when used
with "runtimeType": "io.containerd.runc.v2". For more information about runc
parameters, refer to the runc configuration section in
CRI Plugin Config Guide.
If the runtime that you want to register can act as a drop-in replacement for
runc, you can register the runtime either using the daemon configuration file,
or using the --add-runtime flag for the dockerd cli.
When you use the configuration file, the entry uses the following format:
Where path is either the absolute path to the runtime executable, or the name
of an executable installed on PATH:
{"runtimes":{"runc":{"path":"runc"}}}
And runtimeArgs lets you optionally pass additional arguments to the runtime.
Entries with this format use the containerd runc shim to invoke a custom
runtime binary.
When you use the --add-runtime CLI flag, use the following format:
$ sudo dockerd --add-runtime <runtime>=<path>
Defining runtime arguments via the command line is not supported.
You can specify either the name of a fully qualified containerd runtime shim,
or the name of a registered runtime. You can specify the default runtime either
using the daemon configuration file, or using the --default-runtime flag for
the dockerd cli.
When you use the configuration file, the entry uses the following format:
{"default-runtime":"io.containerd.runsc.v1"}
When you use the --default-runtime CLI flag, use the following format:
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:
You can configure how the runtime should manage container cgroups, using the
--exec-opt native.cgroupdriver CLI flag.
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.
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 non-distributable artifacts to myregistry:5000.
--allow-nondistributable-artifacts 10.1.0.0/16 tells the Docker daemon to
push non-distributable 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 non-distributable artifacts
to a registry on an air-gapped network so hosts on that network can pull the
images without connecting to another server.
Warning
Non-distributable 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 non-distributable artifacts.
In this section, "registry" refers to a private registry, and myregistry:5000
is a placeholder example of a private registry.
Docker considers a private registry either secure or insecure.
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 wasn't found under
/etc/docker/certs.d/myregistry:5000/, or if the certificate verification
failed (i.e., wrong CA).
By default, Docker assumes all registries to be secure, except for local registries.
Communicating with an insecure registry isn't 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 isn't marked as insecure, docker pull,
docker push, and docker search result in error messages, 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 isn't 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.
Operations against registries supporting only the legacy v1 protocol are no longer
supported. Specifically, the daemon doesn't attempt to push, pull or sign in
to v1 registries. The exception to this is search which can still be performed
on v1 registries.
When running inside a LAN that uses an HTTPS proxy, the proxy's certificates
replace Docker Hub's certificates. These certificates must be added to your
Docker host's configuration:
Install the ca-certificates package for your distribution
Ask your network admin for the proxy's CA certificate and append them to
/etc/pki/tls/certs/ca-bundle.crt
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 only adds the proxy and authentication to the Docker daemon's requests.
To use the proxy when building images and running containers, see
Configure Docker to use a proxy server
The --default-ulimit flag lets you set the default ulimit options to use for
all containers. It takes the same options as --ulimit for docker run. If
these defaults aren't set, ulimit settings are inherited from the Docker daemon.
Any --ulimit options passed to docker run override the daemon 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, see
docker run reference.
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.
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 section.
The Linux kernel
user namespace support
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. One of the most important
security improvements is that, by default, container processes running as the
root user have expected administrative privileges it expects (with some restrictions)
inside the container, but are effectively mapped to an unprivileged uid on
the host.
The Docker daemon supports a special host-gateway value for the --add-host
flag for the docker run and docker build commands. This value resolves to
the host's gateway IP and lets containers connect to services running on the
host.
By default, host-gateway resolves to the IP address of the default bridge.
You can configure this to resolve to a different IP using the --host-gateway-ip
flag for the dockerd command line interface, or the host-gateway-ip key in
the daemon configuration file.
This is experimental feature and as such doesn't represent a stable API.
This feature isn't enabled by default. To this feature, set features.cdi to
true in the daemon.json configuration file.
Container Device Interface (CDI) is a
standardized
mechanism for container runtimes to create containers which are able to
interact with third party devices.
The Docker daemon supports running containers with CDI devices if the requested
device specifications are available on the filesystem of the daemon.
The default specification directors are:
/etc/cdi/ for static CDI Specs
/var/run/cdi for generated CDI Specs
Alternatively, you can set custom locations for CDI specifications using the
cdi-spec-dirs option in the daemon.json configuration file, or the
--cdi-spec-dir flag for the dockerd CLI.
When CDI is enabled for a daemon, you can view the configured CDI specification
directories using the docker info command.
Daemon logging format
The --log-format option or "log-format" option in the
daemon configuration file
lets you set the format for logs produced by the daemon. The logging format should
only be configured either through the --log-format command line option or
through the "log-format" field in the configuration file; using both
the command-line option and the "log-format" field in the configuration
file produces an error. If this option is not set, the default is "text".
The following example configures the daemon through the --log-format command
line option to use json formatted logs;
$ dockerd --log-format=json
# ...
{"level":"info","msg":"API listen on /var/run/docker.sock","time":"2024-09-16T11:06:08.558145428Z"}
The following example shows a daemon.json configuration file with the
"log-format" set;
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 soft links 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:
The --cgroup-parent option lets you set the default cgroup parent
for containers. If this option isn't set, it defaults to /docker for
the cgroupfs driver, and system.slice for the 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-<id>.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.
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 format.
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, see
Collect Docker metrics with Prometheus.
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.
The --feature option lets you enable or disable a feature in the daemon.
This option corresponds with the "features" field in the
daemon.json configuration file.
Features should only be configured either through the --feature command line
option or through the "features" field in the 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. The --feature option accepts a name and
optional boolean value. When omitting the value, the default is true.
The following example runs the daemon with the cdi and containerd-snapshotter
features enabled. The cdi option is provided with a value;
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
using flags. The Docker daemon fails to start if an option is duplicated between
the file and the flags, regardless of their value. This is intentional, and avoids
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.
$ 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
You can't 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 can't use the hosts key in daemon.json to add listening addresses.
See
custom Docker daemon options
for an example on how to configure the daemon using systemd drop-in files.
The default location of the configuration file on Windows is
%programdata%\docker\config\daemon.json. Use the --config-file flag
to specify a non-default location.
The following is a full example of the allowed configuration options on Windows:
The default-runtime option is by default unset, in which case dockerd automatically detects the runtime.
This detection is 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.
containerd-snapshotter: when set to true, the daemon uses containerd
snapshotters instead of the classic storage drivers for storing image and
container data. For more information, see
containerd storage.
windows-dns-proxy: when set to true, the daemon's internal DNS resolver
will forward requests to external servers. Without this, most applications
running in the container will still be able to use secondary DNS servers
configured in the container itself, but nslookup won't be able to resolve
external names. The current default is false, it will change to true in
a future release. This option is only allowed on Windows.
Warning
The windows-dns-proxy feature flag will be removed in a future release.
Some options can be reconfigured when the daemon is running without requiring
to restart the process. The daemon uses the SIGHUP signal in Linux to reload,
and a global event in Windows with the key Global\docker-daemon-config-$PID.
You can modify the options in the configuration file, but the daemon still
checks for conflicting settings with the specified CLI 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:
Option
Description
debug
Toggles debug mode of the daemon.
labels
Replaces the daemon labels with a new set of labels.
Running multiple daemons on a single host is considered experimental.
You may encounter unsolved problems, and things may not work as expected in some cases.
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 doesn't
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.
The following daemon options must be configured for each daemon:
-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 important that you understand the meaning of these 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 aren't using the default, you must create and configure the bridge manually, or 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 listens 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 also doesn't add IP masquerading rules, even if you set
--ip-masq to true. Without IP masquerading rules, Docker containers can't
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:
The default-network-opts key in the daemon.json configuration file, and the
equivalent --default-network-opt CLI flag, let you specify default values for
driver network driver options for new networks.
The following example shows how to configure options for the bridge driver
using the daemon.json file.
Note that changing this daemon configuration doesn't affect pre-existing
networks.
Using the --default-network-opt CLI flag is useful for testing and debugging
purposes, but you should prefer using the daemon.json file for persistent
daemon configuration. The CLI flag expects a value with the following format:
driver=opt=value, for example:
