57 KiB
title | aliases | description | keywords | |
---|---|---|---|---|
dockerd |
|
The daemon command description and usage | container, daemon, runtime |
daemon
Usage: dockerd [OPTIONS]
A self-sufficient runtime for containers.
Options:
--add-runtime value Register an additional OCI compatible runtime (default [])
--api-cors-header string Set CORS headers in the Engine API
--authorization-plugin value Authorization plugins to load (default [])
--bip string Specify network bridge IP
-b, --bridge string Attach containers to a network bridge
--cgroup-parent string Set parent cgroup for all containers
--cluster-advertise string Address or interface name to advertise
--cluster-store string URL of the distributed storage backend
--cluster-store-opt value Set cluster store options (default map[])
--config-file string Daemon configuration file (default "/etc/docker/daemon.json")
--containerd string Path to containerd socket
-D, --debug Enable debug mode
--default-gateway value Container default gateway IPv4 address
--default-gateway-v6 value Container default gateway IPv6 address
--default-runtime string Default OCI runtime for containers (default "runc")
--default-shm-size bytes Set the default shm size for containers (default 64 MiB)
--default-ulimit value Default ulimits for containers (default [])
--disable-legacy-registry Disable contacting legacy registries
--dns value DNS server to use (default [])
--dns-opt value DNS options to use (default [])
--dns-search value DNS search domains to use (default [])
--exec-opt value Runtime execution options (default [])
--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, --graph string Root of the Docker runtime (default "/var/lib/docker")
-G, --group string Group for the unix socket (default "docker")
--help Print usage
-H, --host value Daemon socket(s) to connect to (default [])
--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 value Enable insecure registry communication (default [])
--ip value 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)
--ipv6 Enable IPv6 networking
--label value Set key=value labels to the daemon (default [])
--live-restore Enable live restore of docker when containers are still running (Linux only)
--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 value Default log driver options for containers (default map[])
--max-concurrent-downloads int Set the max concurrent downloads for each pull (default 3)
--max-concurrent-uploads int Set the max concurrent uploads for each push (default 5)
--metrics-addr string Set address and port to serve the metrics api (default "")
--mtu int Set the containers network MTU
--no-new-privileges Disable container processes from gaining new privileges
--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 value Preferred Docker registry mirror (default [])
--seccomp-profile value Path to seccomp profile
--selinux-enabled Enable selinux support
--shutdown-timeout=15 Set the shutdown timeout value in seconds
-s, --storage-driver string Storage driver to use
--storage-opt value Storage driver options (default [])
--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 "/root/.docker/ca.pem")
--tlscert string Path to TLS certificate file (default "/root/.docker/cert.pem")
--tlskey string Path to TLS key file (default "/root/.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
-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 -D
.
Examples
Daemon socket option
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.
If you need to access the Docker daemon remotely, you need to enable the tcp
Socket. Beware that the default setup provides un-encrypted and
un-authenticated direct access to the Docker daemon - and should be secured
either using the built in HTTPS encrypted socket, or by
putting a secure web proxy in front of it. You can listen on port 2375
on all
network interfaces with -H tcp://0.0.0.0:2375
, or on a particular network
interface using its IP address: -H tcp://192.168.59.103:2375
. It is
conventional to use port 2375
for un-encrypted, and port 2376
for encrypted
communication with the daemon.
Note: If you're using an HTTPS encrypted socket, keep in mind that only TLS1.0 and greater are supported. Protocols SSLv3 and under are not supported anymore for security reasons.
On Systemd based systems, you can communicate with the daemon via
Systemd socket activation,
use 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.
You can configure the Docker daemon to listen to multiple sockets at the same
time using multiple -H
options:
# listen using the default unix socket, and on 2 specific IP addresses on this host.
$ 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:
$ docker -H tcp://0.0.0.0:2375 ps
$ 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:
$ 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
.
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 todocker
. 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.
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 to127.0.0.1
on either port2376
when TLS encryption is on, or port2375
when communication is in plain text.tcp://host:2375
-> TCP connection on host:2375tcp://host:2375/path
-> TCP connection on host:2375 and prepend path to all requestsunix://path/to/socket
-> Unix socket located atpath/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:
$ 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
# Run docker in daemon mode
$ sudo <path to>/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
The Docker daemon has support for several different image layer storage
drivers: aufs
, devicemapper
, btrfs
, zfs
, overlay
and overlay2
.
The aufs
driver is the oldest, but is based on a Linux kernel patch-set that
is unlikely to be merged into the main kernel. These are also known to cause
some serious kernel crashes. However aufs
allows containers to share
executable and shared library memory, so is a useful choice when running
thousands of containers with the same program or libraries.
The devicemapper
driver uses thin provisioning and Copy on Write (CoW)
snapshots. For each devicemapper graph location – typically
/var/lib/docker/devicemapper
– a thin pool is created based on two block
devices, one for data and one for metadata. By default, these block devices
are created automatically by using loopback mounts of automatically created
sparse files. Refer to Storage driver options below
for a way how to customize this setup.
~jpetazzo/Resizing Docker containers with the Device Mapper plugin
article explains how to tune your existing setup without the use of options.
The btrfs
driver is very fast for docker build
- but like devicemapper
does not share executable memory between devices. Use
dockerd -s btrfs -g /mnt/btrfs_partition
.
The zfs
driver is probably not as fast as btrfs
but has a longer track record
on stability. Thanks to Single Copy ARC
shared blocks between clones will be
cached only once. Use dockerd -s zfs
. To select a different zfs filesystem
set zfs.fsname
option as described in Storage driver options.
The overlay
is a very fast union filesystem. It is now merged in the main
Linux kernel as of 3.18.0. overlay
also supports page cache sharing, this means multiple containers accessing
the same file can share a single page cache entry (or entries), it makes
overlay
as efficient with memory as aufs
driver. Call
dockerd -s overlay
to use it.
Note: As promising as
overlay
is, the feature is still quite young and should not be used in production. Most notably, usingoverlay
can cause excessive inode consumption (especially as the number of images grows), as well as > being incompatible with the use of RPMs.
The overlay2
uses the same fast union filesystem but takes advantage of
additional features added in Linux
kernel 4.0 to avoid excessive inode consumption. Call dockerd -s overlay2
to use it.
Note: Both
overlay
andoverlay2
are currently unsupported onbtrfs
or any Copy on Write filesystem and should only be used overext4
partitions.
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
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:
$ sudo dockerd --storage-opt dm.thinpooldev=/dev/mapper/thin-pool
dm.basesize
Specifies the size to use when creating the base device, which limits the size of images and containers. The default value is 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
$ 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:
$ 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
$ 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
$ 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
$ sudo dockerd --storage-opt dm.fs=ext4
dm.mkfsarg
Specifies extra mkfs arguments to be used when creating the base device.
Example
$ sudo dockerd --storage-opt "dm.mkfsarg=-O ^has_journal"
dm.mountopt
Specifies extra mount options used when mounting the thin devices.
Example
$ 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
$ 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:
$ dd if=/dev/zero of=$metadata_dev bs=4096 count=1
Example
$ 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
$ 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
$ 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:
$ docker info
[...]
Udev Sync Supported: true
[...]
When udev
sync support is true
, then devicemapper
and udev can
coordinate the activation and deactivation of devices for containers.
When udev
sync support is false
, a race condition occurs between
thedevicemapper
and udev
during create and cleanup. The race condition
results in errors and failures. (For information on these failures, see
docker#4036)
To allow the docker
daemon to start, regardless of udev
sync not being
supported, set dm.override_udev_sync_check
to true:
$ 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 withudev
. For further discussion on this topic, see docker#4036. Otherwise, set this flag for migrating existing Docker daemons to a daemon with a supported environment.
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
$ 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.
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.
$ 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
$ 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
$ sudo dockerd --storage-opt dm.xfs_nospace_max_retries=0
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
$ 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
$ sudo dockerd -s btrfs --storage-opt btrfs.min_space=10G
Overlay2 options
overlay2.override_kernel_check
Overrides the Linux kernel version check allowing overlay2. Support for specifying multiple lower directories needed by overlay2 was added to the Linux kernel in 4.0.0. However, some older kernel versions may be patched to add multiple lower directory support for OverlayFS. This option should only be used after verifying this support exists in the kernel. Applying this option on a kernel without this support will cause failures on mount.
Docker runtime execution options
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 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:
$ 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:
{
"default-runtime": "runc",
"runtimes": {
"runc": {
"path": "runc"
},
"custom": {
"path": "/usr/local/bin/my-runc-replacement",
"runtimeArgs": [
"--debug"
]
}
}
}
This is the same example via the command line:
$ sudo dockerd --add-runtime runc=runc --add-runtime custom=/usr/local/bin/my-runc-replacement
Note: Defining runtime arguments via the command line is not supported.
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.
This example sets the cgroupdriver
to systemd
:
$ 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:
> 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:
$ sudo dockerd --dns 8.8.8.8
To set the DNS search domain for all Docker containers, use:
$ sudo dockerd --dns-search example.com
Insecure registries
Docker considers a private registry either secure or insecure. In the rest of
this section, registry is used for private registry, and myregistry:5000
is a placeholder example for a private registry.
A secure registry uses TLS and a copy of its CA certificate is placed on the
Docker host at /etc/docker/certs.d/myregistry:5000/ca.crt
. An insecure
registry is either not using TLS (i.e., listening on plain text HTTP), or is
using TLS with a CA certificate not known by the Docker daemon. The latter can
happen when the certificate was not found under
/etc/docker/certs.d/myregistry:5000/
, or if the certificate verification
failed (i.e., wrong CA).
By default, Docker assumes all, but local (see local registries below),
registries are secure. Communicating with an insecure registry is not possible
if Docker assumes that registry is secure. In order to communicate with an
insecure registry, the Docker daemon requires --insecure-registry
in one of
the following two forms:
--insecure-registry myregistry:5000
tells the Docker daemon that myregistry:5000 should be considered insecure.--insecure-registry 10.1.0.0/16
tells the Docker daemon that all registries whose domain resolve to an IP address is part of the subnet described by the CIDR syntax, should be considered insecure.
The flag can be used multiple times to allow multiple registries to be marked as insecure.
If an insecure registry is not marked as insecure, docker pull
,
docker push
, and docker search
will result in an error message prompting
the user to either secure or pass the --insecure-registry
flag to the Docker
daemon as described above.
Local registries, whose IP address falls in the 127.0.0.0/8 range, are automatically marked as insecure as of Docker 1.3.2. It is not recommended to rely on this, as it may change in the future.
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
Enabling --disable-legacy-registry
forces a docker daemon to only interact with registries which support the V2 protocol. 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:
- 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
. Theusername:
andpassword@
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 reference.
Node discovery
The --cluster-advertise
option specifies the host:port
or interface:port
combination that this particular daemon instance should use when advertising
itself to the cluster. The daemon is reached by remote hosts through this value.
If you specify an interface, make sure it includes the IP address of the actual
Docker host. For Engine installation created through docker-machine
, the
interface is typically eth1
.
The daemon uses libkv to advertise
the node within the cluster. Some key-value backends support mutual
TLS. To configure the client TLS settings used by the daemon can be configured
using the --cluster-store-opt
flag, specifying the paths to PEM encoded
files. For example:
$ sudo dockerd \
--cluster-advertise 192.168.1.2:2376 \
--cluster-store etcd://192.168.1.2:2379 \
--cluster-store-opt kv.cacertfile=/path/to/ca.pem \
--cluster-store-opt kv.certfile=/path/to/cert.pem \
--cluster-store-opt kv.keyfile=/path/to/key.pem
The currently supported cluster store options are:
Option | Description |
---|---|
discovery.heartbeat |
Specifies the heartbeat timer in seconds which is used by the daemon as a keepalive mechanism to make sure discovery module treats the node as alive in the cluster. If not configured, the default value is 20 seconds. |
discovery.ttl |
Specifies the TTL (time-to-live) in seconds which is used by the discovery module to timeout a node if a valid heartbeat is not received within the configured ttl value. If not configured, the default value is 60 seconds. |
kv.cacertfile |
Specifies the path to a local file with PEM encoded CA certificates to trust. |
kv.certfile |
Specifies the path to a local file with a PEM encoded certificate. This certificate is used as the client cert for communication with the Key/Value store. |
kv.keyfile |
Specifies the path to a local file with a PEM encoded private key. This private key is used as the client key for communication with the Key/Value store. |
kv.path |
Specifies the path in the Key/Value store. If not configured, the default value is 'docker/nodes'. |
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.
$ 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, at least one must allow the request for it to
complete.
For information about how to create an authorization plugin, see authorization plugin section in the Docker extend section of this documentation.
Daemon user namespace options
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. 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.
When user namespace support is enabled, Docker creates a single daemon-wide mapping
for all containers running on the same engine instance. The mappings will
utilize the existing subordinate user and group ID feature available on all modern
Linux distributions.
The /etc/subuid
and
/etc/subgid
files will be
read for the user, and optional group, specified to the --userns-remap
parameter. If you do not wish to specify your own user and/or group, you can
provide default
as the value to this flag, and a user will be created on your behalf
and provided subordinate uid and gid ranges. This default user will be named
dockremap
, and entries will be created for it in /etc/passwd
and
/etc/group
using your distro's standard user and group creation tools.
Note: The single mapping per-daemon restriction is in place for now because Docker shares image layers from its local cache across all containers running on the engine instance. Since file ownership must be the same for all containers sharing the same layer content, the decision was made to map the file ownership on
docker pull
to the daemon's user and group mappings so that there is no delay for running containers once the content is downloaded. This design preserves the same performance fordocker pull
,docker push
, and container startup as users expect with user namespaces disabled.
Start the daemon with user namespaces enabled
To enable user namespace support, start the daemon with the
--userns-remap
flag, which accepts values in the following formats:
- uid
- uid:gid
- username
- username:groupname
If numeric IDs are provided, translation back to valid user or group names
will occur so that the subordinate uid and gid information can be read, given
these resources are name-based, not id-based. If the numeric ID information
provided does not exist as entries in /etc/passwd
or /etc/group
, daemon
startup will fail with an error message.
Example: starting with default Docker user management:
$ sudo dockerd --userns-remap=default
When default
is provided, Docker will create - or find the existing - user and group
named dockremap
. If the user is created, and the Linux distribution has
appropriate support, the /etc/subuid
and /etc/subgid
files will be populated
with a contiguous 65536 length range of subordinate user and group IDs, starting
at an offset based on prior entries in those files. For example, Ubuntu will
create the following range, based on an existing user named user1
already owning
the first 65536 range:
$ cat /etc/subuid
user1:100000:65536
dockremap:165536:65536
If you have a preferred/self-managed user with subordinate ID mappings already
configured, you can provide that username or uid to the --userns-remap
flag.
If you have a group that doesn't match the username, you may provide the gid
or group name as well; otherwise the username will be used as the group name
when querying the system for the subordinate group ID range.
The output of docker info
can be used to determine if the daemon is running
with user namespaces enabled or not. If the daemon is configured with user
namespaces, the Security Options entry in the response will list "userns" as
one of the enabled security features.
Behavior differences when user namespaces are enabled
When you start the Docker daemon with --userns-remap
, Docker segregates the graph directory
where the images are stored by adding an extra directory with a name corresponding to the
remapped UID and GID. For example, if the remapped UID and GID begin with 165536
, all
images and containers running with that remap setting are located in /var/lib/docker/165536.165536
instead of /var/lib/docker/
.
In addition, the files and directories within the new directory, which correspond to
images and container layers, are also owned by the new UID and GID. To set the ownership
correctly, you need to re-pull the images and restart the containers after starting the
daemon with --userns-remap
.
Detailed information on subuid
/subgid
ranges
Given potential advanced use of the subordinate ID ranges by power users, the following paragraphs define how the Docker daemon currently uses the range entries found within the subordinate range files.
The simplest case is that only one contiguous range is defined for the provided user or group. In this case, Docker will use that entire contiguous range for the mapping of host uids and gids to the container process. This means that the first ID in the range will be the remapped root user, and the IDs above that initial ID will map host ID 1 through the end of the range.
From the example /etc/subuid
content shown above, the remapped root
user would be uid 165536.
If the system administrator has set up multiple ranges for a single user or group, the Docker daemon will read all the available ranges and use the following algorithm to create the mapping ranges:
- The range segments found for the particular user will be sorted by start ID ascending.
- Map segments will be created from each range in increasing value with a length matching the length of each segment. Therefore the range segment with the lowest numeric starting value will be equal to the remapped root, and continue up through host uid/gid equal to the range segment length. As an example, if the lowest segment starts at ID 1000 and has a length of 100, then a map of 1000 -> 0 (the remapped root) up through 1100 -> 100 will be created from this segment. If the next segment starts at ID 10000, then the next map will start with mapping 10000 -> 101 up to the length of this second segment. This will continue until no more segments are found in the subordinate files for this user.
- If more than five range segments exist for a single user, only the first five will be utilized, matching the kernel's limitation of only five entries in
/proc/self/uid_map
andproc/self/gid_map
.
Disable user namespace for a container
If you enable user namespaces on the daemon, all containers are started
with user namespaces enabled. In some situations you might want to disable
this feature for a container, for example, to start a privileged container (see
user namespace known restrictions).
To enable those advanced features for a specific container use --userns=host
in the run/exec/create
command.
This option will completely disable user namespace mapping for the container's user.
User namespace known restrictions
The following standard Docker features are currently incompatible when running a Docker daemon with user namespaces enabled:
- sharing PID or NET namespaces with the host (
--pid=host
or--net=host
) - Using
--privileged
mode flag ondocker run
(unless also specifying--userns=host
)
In general, user namespaces are an advanced feature and will require coordination with other capabilities. For example, if volumes are mounted from the host, file ownership will have to be pre-arranged if the user or administrator wishes the containers to have expected access to the volume contents. Note that when using external volume or graph driver plugins, those external software programs must be made aware of user and group mapping ranges if they are to work seamlessly with user namespace support.
Finally, while the root
user inside a user namespaced container process has
many of the expected admin privileges that go along with being the superuser, the
Linux kernel has restrictions based on internal knowledge that this is a user namespaced
process. The most notable restriction that we are aware of at this time is the
inability to use mknod
. Permission will be denied for device creation even as
container root
inside a user namespace.
Miscellaneous options
IP masquerading uses address translation to allow containers without a public
IP to talk to other machines on the Internet. This may interfere with some
network topologies and can be disabled with --ip-masq=false
.
Docker supports softlinks for the Docker data directory (/var/lib/docker
) and
for /var/lib/docker/tmp
. The DOCKER_TMPDIR
and the data directory can be
set like this:
DOCKER_TMPDIR=/mnt/disk2/tmp /usr/local/bin/dockerd -D -g /var/lib/docker -H unix:// > /var/lib/docker-machine/docker.log 2>&1
# or
export DOCKER_TMPDIR=/mnt/disk2/tmp
/usr/local/bin/dockerd -D -g /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-<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.
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:1337 you would specify --metrics-addr 127.0.0.1:1337
allowing you to make requests on the API at 127.0.0.1:1337/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 on prometheus you can view the website here.
scrape_configs:
- job_name: 'docker'
static_configs:
- targets: ['127.0.0.1:1337']
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.
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 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.
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:
{
"authorization-plugins": [],
"dns": [],
"dns-opts": [],
"dns-search": [],
"exec-opts": [],
"exec-root": "",
"experimental": false,
"storage-driver": "",
"storage-opts": [],
"labels": [],
"live-restore": true,
"log-driver": "",
"log-opts": {},
"mtu": 0,
"pidfile": "",
"graph": "",
"cluster-store": "",
"cluster-store-opts": {},
"cluster-advertise": "",
"max-concurrent-downloads": 3,
"max-concurrent-uploads": 5,
"default-shm-size": "64M",
"shutdown-timeout": 15,
"debug": true,
"hosts": [],
"log-level": "",
"tls": true,
"tlsverify": true,
"tlscacert": "",
"tlscert": "",
"tlskey": "",
"swarm-default-advertise-addr": "",
"api-cors-header": "",
"selinux-enabled": false,
"userns-remap": "",
"group": "",
"cgroup-parent": "",
"default-ulimits": {},
"init": false,
"init-path": "/usr/libexec/docker-init",
"ipv6": false,
"iptables": false,
"ip-forward": false,
"ip-masq": false,
"userland-proxy": false,
"userland-proxy-path": "/usr/libexec/docker-proxy",
"ip": "0.0.0.0",
"bridge": "",
"bip": "",
"fixed-cidr": "",
"fixed-cidr-v6": "",
"default-gateway": "",
"default-gateway-v6": "",
"icc": false,
"raw-logs": false,
"registry-mirrors": [],
"seccomp-profile": "",
"insecure-registries": [],
"disable-legacy-registry": false,
"no-new-privileges": false,
"default-runtime": "runc",
"oom-score-adjust": -500,
"runtimes": {
"runc": {
"path": "runc"
},
"custom": {
"path": "/usr/local/bin/my-runc-replacement",
"runtimeArgs": [
"--debug"
]
}
}
}
Note: You cannot set options in
daemon.json
that have already been set on daemon startup as a flag. On systems that usesystemd
to start the Docker daemon,-H
is already set, so you cannot use thehosts
key indaemon.json
to add listening addresses. See https://docs.docker.com/engine/admin/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:
{
"authorization-plugins": [],
"dns": [],
"dns-opts": [],
"dns-search": [],
"exec-opts": [],
"experimental": false,
"storage-driver": "",
"storage-opts": [],
"labels": [],
"log-driver": "",
"mtu": 0,
"pidfile": "",
"graph": "",
"cluster-store": "",
"cluster-advertise": "",
"max-concurrent-downloads": 3,
"max-concurrent-uploads": 5,
"shutdown-timeout": 15,
"debug": true,
"hosts": [],
"log-level": "",
"tlsverify": true,
"tlscacert": "",
"tlscert": "",
"tlskey": "",
"swarm-default-advertise-addr": "",
"group": "",
"default-ulimits": {},
"bridge": "",
"fixed-cidr": "",
"raw-logs": false,
"registry-mirrors": [],
"insecure-registries": [],
"disable-legacy-registry": false
}
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.cluster-store
: it reloads the discovery store with the new address.cluster-store-opts
: it uses the new options to reload the discovery store.cluster-advertise
: it modifies the address advertised after reloading.labels
: it replaces the daemon labels with a new set of labels.live-restore
: Enables keeping containers alive during daemon downtime.max-concurrent-downloads
: it updates the max concurrent downloads for each pull.max-concurrent-uploads
: it updates the max concurrent uploads for each push.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 containersauthorization-plugin
: specifies the authorization plugins to use.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 resgitries, 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.
Updating and reloading the cluster configurations such as --cluster-store
,
--cluster-advertise
and --cluster-store-opts
will take effect only if
these configurations were not previously configured. If --cluster-store
has been provided in flags and cluster-advertise
not, cluster-advertise
can be added in the configuration file without accompanied by --cluster-store
.
Configuration reload will log a warning message if it detects a change in
previously configured cluster configurations.
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.
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
-g, --graph=/var/lib/docker Root of the Docker runtime
-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 todocker0
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.--graph
is the path where images 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
totrue
. 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:
$ sudo dockerd \
-H unix:///var/run/docker-bootstrap.sock \
-p /var/run/docker-bootstrap.pid \
--iptables=false \
--ip-masq=false \
--bridge=none \
--graph=/var/lib/docker-bootstrap \
--exec-root=/var/run/docker-bootstrap