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---
title: "run"
description: "The run command description and usage"
keywords: "run, command, container"
---
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repository at https://github.com/docker/cli/. Make all
pull requests against that repo. If you see this file in
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# run
```markdown
Usage: docker run [OPTIONS] IMAGE [COMMAND] [ARG...]
Run a command in a new container
Options:
--add-host value Add a custom host-to-IP mapping (host:ip) (default [])
-a, --attach value Attach to STDIN, STDOUT or STDERR (default [])
--blkio-weight value Block IO (relative weight), between 10 and 1000
--blkio-weight-device value Block IO weight (relative device weight) (default [])
--cap-add value Add Linux capabilities (default [])
--cap-drop value Drop Linux capabilities (default [])
--cgroup-parent string Optional parent cgroup for the container
--cidfile string Write the container ID to the file
--cpu-count int The number of CPUs available for execution by the container.
Windows daemon only. On Windows Server containers, this is
approximated as a percentage of total CPU usage.
--cpu-percent int Limit percentage of CPU available for execution
by the container. Windows daemon only.
The processor resource controls are mutually
exclusive, the order of precedence is CPUCount
first, then CPUShares, and CPUPercent last.
--cpu-period int Limit CPU CFS (Completely Fair Scheduler) period
--cpu-quota int Limit CPU CFS (Completely Fair Scheduler) quota
-c, --cpu-shares int CPU shares (relative weight)
--cpus NanoCPUs Number of CPUs (default 0.000)
--cpu-rt-period int Limit the CPU real-time period in microseconds
--cpu-rt-runtime int Limit the CPU real-time runtime in microseconds
--cpuset-cpus string CPUs in which to allow execution (0-3, 0,1)
--cpuset-mems string MEMs in which to allow execution (0-3, 0,1)
-d, --detach Run container in background and print container ID
--detach-keys string Override the key sequence for detaching a container
--device value Add a host device to the container (default [])
--device-cgroup-rule value Add a rule to the cgroup allowed devices list
--device-read-bps value Limit read rate (bytes per second) from a device (default [])
--device-read-iops value Limit read rate (IO per second) from a device (default [])
--device-write-bps value Limit write rate (bytes per second) to a device (default [])
--device-write-iops value Limit write rate (IO per second) to a device (default [])
--disable-content-trust Skip image verification (default true)
--dns value Set custom DNS servers (default [])
--dns-option value Set DNS options (default [])
--dns-search value Set custom DNS search domains (default [])
--domainname string Container NIS domain name
--entrypoint string Overwrite the default ENTRYPOINT of the image
-e, --env value Set environment variables (default [])
--env-file value Read in a file of environment variables (default [])
--expose value Expose a port or a range of ports (default [])
--group-add value Add additional groups to join (default [])
--health-cmd string Command to run to check health
--health-interval duration Time between running the check (ns|us|ms|s|m|h) (default 0s)
--health-retries int Consecutive failures needed to report unhealthy
--health-timeout duration Maximum time to allow one check to run (ns|us|ms|s|m|h) (default 0s)
--health-start-period duration Start period for the container to initialize before counting retries towards unstable (ns|us|ms|s|m|h) (default 0s)
--help Print usage
-h, --hostname string Container host name
--init Run an init inside the container that forwards signals and reaps processes
-i, --interactive Keep STDIN open even if not attached
--io-maxbandwidth string Maximum IO bandwidth limit for the system drive (Windows only)
(Windows only). The format is `<number><unit>`.
Unit is optional and can be `b` (bytes per second),
`k` (kilobytes per second), `m` (megabytes per second),
or `g` (gigabytes per second). If you omit the unit,
the system uses bytes per second.
--io-maxbandwidth and --io-maxiops are mutually exclusive options.
--io-maxiops uint Maximum IOps limit for the system drive (Windows only)
--ip string IPv4 address (e.g., 172.30.100.104)
--ip6 string IPv6 address (e.g., 2001:db8::33)
--ipc string IPC namespace to use
--isolation string Container isolation technology
--kernel-memory string Kernel memory limit
-l, --label value Set meta data on a container (default [])
--label-file value Read in a line delimited file of labels (default [])
--link value Add link to another container (default [])
--link-local-ip value Container IPv4/IPv6 link-local addresses (default [])
--log-driver string Logging driver for the container
--log-opt value Log driver options (default [])
--mac-address string Container MAC address (e.g., 92:d0:c6:0a:29:33)
-m, --memory string Memory limit
--memory-reservation string Memory soft limit
--memory-swap string Swap limit equal to memory plus swap: '-1' to enable unlimited swap
--memory-swappiness int Tune container memory swappiness (0 to 100) (default -1)
--mount value Attach a filesystem mount to the container (default [])
--name string Assign a name to the container
--network-alias value Add network-scoped alias for the container (default [])
--network string Connect a container to a network
'bridge': create a network stack on the default Docker bridge
'none': no networking
'container:<name|id>': reuse another container's network stack
'host': use the Docker host network stack
'<network-name>|<network-id>': connect to a user-defined network
--no-healthcheck Disable any container-specified HEALTHCHECK
--oom-kill-disable Disable OOM Killer
--oom-score-adj int Tune host's OOM preferences (-1000 to 1000)
--pid string PID namespace to use
--pids-limit int Tune container pids limit (set -1 for unlimited)
--privileged Give extended privileges to this container
-p, --publish value Publish a container's port(s) to the host (default [])
-P, --publish-all Publish all exposed ports to random ports
--read-only Mount the container's root filesystem as read only
--restart string Restart policy to apply when a container exits (default "no")
Possible values are : no, on-failure[:max-retry], always, unless-stopped
--rm Automatically remove the container when it exits
--runtime string Runtime to use for this container
--security-opt value Security Options (default [])
--shm-size bytes Size of /dev/shm
The format is `<number><unit>`. `number` must be greater than `0`.
Unit is optional and can be `b` (bytes), `k` (kilobytes), `m` (megabytes),
or `g` (gigabytes). If you omit the unit, the system uses bytes.
--sig-proxy Proxy received signals to the process (default true)
--stop-signal string Signal to stop a container (default "SIGTERM")
--stop-timeout=10 Timeout (in seconds) to stop a container
--storage-opt value Storage driver options for the container (default [])
--sysctl value Sysctl options (default map[])
--tmpfs value Mount a tmpfs directory (default [])
-t, --tty Allocate a pseudo-TTY
--ulimit value Ulimit options (default [])
-u, --user string Username or UID (format: <name|uid>[:<group|gid>])
--userns string User namespace to use
'host': Use the Docker host user namespace
'': Use the Docker daemon user namespace specified by `--userns-remap` option.
--uts string UTS namespace to use
-v, --volume value Bind mount a volume (default []). The format
is `[host-src:]container-dest[:<options>]`.
The comma-delimited `options` are [rw|ro],
[z|Z], [[r]shared|[r]slave|[r]private],
[delegated|cached|consistent], and
[nocopy]. The 'host-src' is an absolute path
or a name value.
--volume-driver string Optional volume driver for the container
--volumes-from value Mount volumes from the specified container(s) (default [])
-w, --workdir string Working directory inside the container
```
## Description
The `docker run` command first `creates` a writeable container layer over the
specified image, and then `starts` it using the specified command. That is,
`docker run` is equivalent to the API `/containers/create` then
`/containers/(id)/start`. A stopped container can be restarted with all its
previous changes intact using `docker start`. See `docker ps -a` to view a list
of all containers.
The `docker run` command can be used in combination with `docker commit` to
[*change the command that a container runs*](commit.md). There is additional detailed information about `docker run` in the [Docker run reference](../run.md).
For information on connecting a container to a network, see the ["*Docker network overview*"](https://docs.docker.com/engine/userguide/networking/).
## Examples
### Assign name and allocate pseudo-TTY (--name, -it)
```bash
$ docker run --name test -it debian
root@d6c0fe130dba:/# exit 13
$ echo $?
13
$ docker ps -a | grep test
d6c0fe130dba debian:7 "/bin/bash" 26 seconds ago Exited (13) 17 seconds ago test
```
This example runs a container named `test` using the `debian:latest`
image. The `-it` instructs Docker to allocate a pseudo-TTY connected to
the container's stdin; creating an interactive `bash` shell in the container.
In the example, the `bash` shell is quit by entering
`exit 13`. This exit code is passed on to the caller of
`docker run`, and is recorded in the `test` container's metadata.
### Capture container ID (--cidfile)
```bash
$ docker run --cidfile /tmp/docker_test.cid ubuntu echo "test"
```
This will create a container and print `test` to the console. The `cidfile`
flag makes Docker attempt to create a new file and write the container ID to it.
If the file exists already, Docker will return an error. Docker will close this
file when `docker run` exits.
### Full container capabilities (--privileged)
```bash
$ docker run -t -i --rm ubuntu bash
root@bc338942ef20:/# mount -t tmpfs none /mnt
mount: permission denied
```
This will *not* work, because by default, most potentially dangerous kernel
capabilities are dropped; including `cap_sys_admin` (which is required to mount
filesystems). However, the `--privileged` flag will allow it to run:
```bash
$ docker run -t -i --privileged ubuntu bash
root@50e3f57e16e6:/# mount -t tmpfs none /mnt
root@50e3f57e16e6:/# df -h
Filesystem Size Used Avail Use% Mounted on
none 1.9G 0 1.9G 0% /mnt
```
The `--privileged` flag gives *all* capabilities to the container, and it also
lifts all the limitations enforced by the `device` cgroup controller. In other
words, the container can then do almost everything that the host can do. This
flag exists to allow special use-cases, like running Docker within Docker.
### Set working directory (-w)
```bash
$ docker run -w /path/to/dir/ -i -t ubuntu pwd
```
The `-w` lets the command being executed inside directory given, here
`/path/to/dir/`. If the path does not exist it is created inside the container.
### Set storage driver options per container
```bash
$ docker run -it --storage-opt size=120G fedora /bin/bash
```
This (size) will allow to set the container rootfs size to 120G at creation time.
This option is only available for the `devicemapper`, `btrfs`, `overlay2`,
`windowsfilter` and `zfs` graph drivers.
For the `devicemapper`, `btrfs`, `windowsfilter` and `zfs` graph drivers,
user cannot pass a size less than the Default BaseFS Size.
For the `overlay2` storage driver, the size option is only available if the
backing fs is `xfs` and mounted with the `pquota` mount option.
Under these conditions, user can pass any size less than the backing fs size.
### Mount tmpfs (--tmpfs)
```bash
$ docker run -d --tmpfs /run:rw,noexec,nosuid,size=65536k my_image
```
The `--tmpfs` flag mounts an empty tmpfs into the container with the `rw`,
`noexec`, `nosuid`, `size=65536k` options.
### Mount volume (-v, --read-only)
```bash
$ docker run -v `pwd`:`pwd` -w `pwd` -i -t ubuntu pwd
```
The `-v` flag mounts the current working directory into the container. The `-w`
lets the command being executed inside the current working directory, by
changing into the directory to the value returned by `pwd`. So this
combination executes the command using the container, but inside the
current working directory.
```bash
$ docker run -v /doesnt/exist:/foo -w /foo -i -t ubuntu bash
```
When the host directory of a bind-mounted volume doesn't exist, Docker
will automatically create this directory on the host for you. In the
example above, Docker will create the `/doesnt/exist`
folder before starting your container.
```bash
$ docker run --read-only -v /icanwrite busybox touch /icanwrite/here
```
Volumes can be used in combination with `--read-only` to control where
a container writes files. The `--read-only` flag mounts the container's root
filesystem as read only prohibiting writes to locations other than the
specified volumes for the container.
```bash
$ docker run -t -i -v /var/run/docker.sock:/var/run/docker.sock -v /path/to/static-docker-binary:/usr/bin/docker busybox sh
```
By bind-mounting the docker unix socket and statically linked docker
binary (refer to [get the linux binary](
https://docs.docker.com/engine/installation/binaries/#/get-the-linux-binary)),
you give the container the full access to create and manipulate the host's
Docker daemon.
On Windows, the paths must be specified using Windows-style semantics.
```powershell
PS C:\> docker run -v c:\foo:c:\dest microsoft/nanoserver cmd /s /c type c:\dest\somefile.txt
Contents of file
PS C:\> docker run -v c:\foo:d: microsoft/nanoserver cmd /s /c type d:\somefile.txt
Contents of file
```
The following examples will fail when using Windows-based containers, as the
destination of a volume or bind mount inside the container must be one of:
a non-existing or empty directory; or a drive other than C:. Further, the source
of a bind mount must be a local directory, not a file.
```powershell
net use z: \\remotemachine\share
docker run -v z:\foo:c:\dest ...
docker run -v \\uncpath\to\directory:c:\dest ...
docker run -v c:\foo\somefile.txt:c:\dest ...
docker run -v c:\foo:c: ...
docker run -v c:\foo:c:\existing-directory-with-contents ...
```
For in-depth information about volumes, refer to [manage data in containers](https://docs.docker.com/engine/tutorials/dockervolumes/)
### Add bind mounts or volumes using the --mount flag
The `--mount` flag allows you to mount volumes, host-directories and `tmpfs`
mounts in a container.
The `--mount` flag supports most options that are supported by the `-v` or the
`--volume` flag, but uses a different syntax. For in-depth information on the
`--mount` flag, and a comparison between `--volume` and `--mount`, refer to
the [service create command reference](service_create.md#add-bind-mounts-or-volumes).
Even though there is no plan to deprecate `--volume`, usage of `--mount` is recommended.
Examples:
```bash
$ docker run --read-only --mount type=volume,target=/icanwrite busybox touch /icanwrite/here
```
```bash
$ docker run -t -i --mount type=bind,src=/data,dst=/data busybox sh
```
### Publish or expose port (-p, --expose)
```bash
$ docker run -p 127.0.0.1:80:8080/tcp ubuntu bash
```
This binds port `8080` of the container to TCP port `80` on `127.0.0.1` of the host
machine. You can also specify `udp` and `sctp` ports.
The [Docker User Guide](https://docs.docker.com/engine/userguide/networking/default_network/dockerlinks/)
explains in detail how to manipulate ports in Docker.
```bash
$ docker run --expose 80 ubuntu bash
```
This exposes port `80` of the container without publishing the port to the host
system's interfaces.
### Set environment variables (-e, --env, --env-file)
```bash
$ docker run -e MYVAR1 --env MYVAR2=foo --env-file ./env.list ubuntu bash
```
Use the `-e`, `--env`, and `--env-file` flags to set simple (non-array)
environment variables in the container you're running, or overwrite variables
that are defined in the Dockerfile of the image you're running.
You can define the variable and its value when running the container:
```bash
$ docker run --env VAR1=value1 --env VAR2=value2 ubuntu env | grep VAR
VAR1=value1
VAR2=value2
```
You can also use variables that you've exported to your local environment:
```bash
export VAR1=value1
export VAR2=value2
$ docker run --env VAR1 --env VAR2 ubuntu env | grep VAR
VAR1=value1
VAR2=value2
```
When running the command, the Docker CLI client checks the value the variable
has in your local environment and passes it to the container.
If no `=` is provided and that variable is not exported in your local
environment, the variable won't be set in the container.
You can also load the environment variables from a file. This file should use
the syntax `<variable>=value` (which sets the variable to the given value) or
`<variable>` (which takes the value from the local environment), and `#` for comments.
```bash
$ cat env.list
# This is a comment
VAR1=value1
VAR2=value2
USER
$ docker run --env-file env.list ubuntu env | grep VAR
VAR1=value1
VAR2=value2
USER=denis
```
### Set metadata on container (-l, --label, --label-file)
A label is a `key=value` pair that applies metadata to a container. To label a container with two labels:
```bash
$ docker run -l my-label --label com.example.foo=bar ubuntu bash
```
The `my-label` key doesn't specify a value so the label defaults to an empty
string (`""`). To add multiple labels, repeat the label flag (`-l` or `--label`).
The `key=value` must be unique to avoid overwriting the label value. If you
specify labels with identical keys but different values, each subsequent value
overwrites the previous. Docker uses the last `key=value` you supply.
Use the `--label-file` flag to load multiple labels from a file. Delimit each
label in the file with an EOL mark. The example below loads labels from a
labels file in the current directory:
```bash
$ docker run --label-file ./labels ubuntu bash
```
The label-file format is similar to the format for loading environment
variables. (Unlike environment variables, labels are not visible to processes
running inside a container.) The following example illustrates a label-file
format:
```none
com.example.label1="a label"
# this is a comment
com.example.label2=another\ label
com.example.label3
```
You can load multiple label-files by supplying multiple `--label-file` flags.
For additional information on working with labels, see [*Labels - custom
metadata in Docker*](https://docs.docker.com/engine/userguide/labels-custom-metadata/) in the Docker User
Guide.
### Connect a container to a network (--network)
When you start a container use the `--network` flag to connect it to a network.
This adds the `busybox` container to the `my-net` network.
```bash
$ docker run -itd --network=my-net busybox
```
You can also choose the IP addresses for the container with `--ip` and `--ip6`
flags when you start the container on a user-defined network.
```bash
$ docker run -itd --network=my-net --ip=10.10.9.75 busybox
```
If you want to add a running container to a network use the `docker network connect` subcommand.
You can connect multiple containers to the same network. Once connected, the
containers can communicate easily need only another container's IP address
or name. For `overlay` networks or custom plugins that support multi-host
connectivity, containers connected to the same multi-host network but launched
from different Engines can also communicate in this way.
> **Note**: Service discovery is unavailable on the default bridge network.
> Containers can communicate via their IP addresses by default. To communicate
> by name, they must be linked.
You can disconnect a container from a network using the `docker network
disconnect` command.
### Mount volumes from container (--volumes-from)
```bash
$ docker run --volumes-from 777f7dc92da7 --volumes-from ba8c0c54f0f2:ro -i -t ubuntu pwd
```
The `--volumes-from` flag mounts all the defined volumes from the referenced
containers. Containers can be specified by repetitions of the `--volumes-from`
argument. The container ID may be optionally suffixed with `:ro` or `:rw` to
mount the volumes in read-only or read-write mode, respectively. By default,
the volumes are mounted in the same mode (read write or read only) as
the reference container.
Labeling systems like SELinux require that proper labels are placed on volume
content mounted into a container. Without a label, the security system might
prevent the processes running inside the container from using the content. By
default, Docker does not change the labels set by the OS.
To change the label in the container context, you can add either of two suffixes
`:z` or `:Z` to the volume mount. These suffixes tell Docker to relabel file
objects on the shared volumes. The `z` option tells Docker that two containers
share the volume content. As a result, Docker labels the content with a shared
content label. Shared volume labels allow all containers to read/write content.
The `Z` option tells Docker to label the content with a private unshared label.
Only the current container can use a private volume.
### Attach to STDIN/STDOUT/STDERR (-a)
The `-a` flag tells `docker run` to bind to the container's `STDIN`, `STDOUT`
or `STDERR`. This makes it possible to manipulate the output and input as
needed.
```bash
$ echo "test" | docker run -i -a stdin ubuntu cat -
```
This pipes data into a container and prints the container's ID by attaching
only to the container's `STDIN`.
```bash
$ docker run -a stderr ubuntu echo test
```
This isn't going to print anything unless there's an error because we've
only attached to the `STDERR` of the container. The container's logs
still store what's been written to `STDERR` and `STDOUT`.
```bash
$ cat somefile | docker run -i -a stdin mybuilder dobuild
```
This is how piping a file into a container could be done for a build.
The container's ID will be printed after the build is done and the build
logs could be retrieved using `docker logs`. This is
useful if you need to pipe a file or something else into a container and
retrieve the container's ID once the container has finished running.
### Add host device to container (--device)
```bash
$ docker run --device=/dev/sdc:/dev/xvdc \
--device=/dev/sdd --device=/dev/zero:/dev/nulo \
-i -t \
ubuntu ls -l /dev/{xvdc,sdd,nulo}
brw-rw---- 1 root disk 8, 2 Feb 9 16:05 /dev/xvdc
brw-rw---- 1 root disk 8, 3 Feb 9 16:05 /dev/sdd
crw-rw-rw- 1 root root 1, 5 Feb 9 16:05 /dev/nulo
```
It is often necessary to directly expose devices to a container. The `--device`
option enables that. For example, a specific block storage device or loop
device or audio device can be added to an otherwise unprivileged container
(without the `--privileged` flag) and have the application directly access it.
By default, the container will be able to `read`, `write` and `mknod` these devices.
This can be overridden using a third `:rwm` set of options to each `--device`
flag:
```bash
$ docker run --device=/dev/sda:/dev/xvdc --rm -it ubuntu fdisk /dev/xvdc
Command (m for help): q
$ docker run --device=/dev/sda:/dev/xvdc:r --rm -it ubuntu fdisk /dev/xvdc
You will not be able to write the partition table.
Command (m for help): q
$ docker run --device=/dev/sda:/dev/xvdc:rw --rm -it ubuntu fdisk /dev/xvdc
Command (m for help): q
$ docker run --device=/dev/sda:/dev/xvdc:m --rm -it ubuntu fdisk /dev/xvdc
fdisk: unable to open /dev/xvdc: Operation not permitted
```
> **Note**: `--device` cannot be safely used with ephemeral devices. Block devices
> that may be removed should not be added to untrusted containers with
> `--device`.
For Windows, the format of the string passed to the `--device` option is in
the form of `--device=<IdType>/<Id>`. Beginning with Windows Server 2019
and Windows 10 October 2018 Update, Windows only supports an IdType of
`class` and the Id as a [device interface class
GUID](https://docs.microsoft.com/en-us/windows-hardware/drivers/install/overview-of-device-interface-classes).
Refer to the table defined in the [Windows container
docs](https://docs.microsoft.com/en-us/virtualization/windowscontainers/deploy-containers/hardware-devices-in-containers)
for a list of container-supported device interface class GUIDs.
If this option is specified for a process-isolated Windows container, _all_
devices that implement the requested device interface class GUID are made
available in the container. For example, the command below makes all COM
ports on the host visible in the container.
```powershell
PS C:\> docker run --device=class/86E0D1E0-8089-11D0-9CE4-08003E301F73 mcr.microsoft.com/windows/servercore:ltsc2019
```
> **Note**: the `--device` option is only supported on process-isolated
> Windows containers. This option fails if the container isolation is `hyperv`
> or when running Linux Containers on Windows (LCOW).
### Access an NVIDIA GPU
The `--gpus­` flag allows you to access NVIDIA GPU resources. First you need to
install [nvidia-container-runtime](https://nvidia.github.io/nvidia-container-runtime/).
Visit [Specify a container's resources](https://docs.docker.com/config/containers/resource_constraints/)
for more information.
To use `--gpus`, specify which GPUs (or all) to use. If no value is provied, all
available GPUs are used. The example below exposes all available GPUs.
```bash
$ docker run -it --rm --gpus all ubuntu nvidia-smi
```
Use the `device` option to specify GPUs. The example below exposes a specific
GPU.
```bash
$ docker run -it --rm --gpus device=GPU-3a23c669-1f69-c64e-cf85-44e9b07e7a2a ubuntu nvidia-smi
```
The example below exposes the first and third GPUs.
```bash
$ docker run -it --rm --gpus device=0,2 nvidia-smi
```
### Restart policies (--restart)
Use Docker's `--restart` to specify a container's *restart policy*. A restart
policy controls whether the Docker daemon restarts a container after exit.
Docker supports the following restart policies:
| Policy | Result |
|:---------------------------|:-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| `no` | Do not automatically restart the container when it exits. This is the default. |
| `on-failure[:max-retries]` | Restart only if the container exits with a non-zero exit status. Optionally, limit the number of restart retries the Docker daemon attempts. |
| `unless-stopped` | Restart the container unless it is explicitly stopped or Docker itself is stopped or restarted. |
| `always` | Always restart the container regardless of the exit status. When you specify always, the Docker daemon will try to restart the container indefinitely. The container will also always start on daemon startup, regardless of the current state of the container. |
```bash
$ docker run --restart=always redis
```
This will run the `redis` container with a restart policy of **always**
so that if the container exits, Docker will restart it.
More detailed information on restart policies can be found in the
[Restart Policies (--restart)](../run.md#restart-policies---restart)
section of the Docker run reference page.
### Add entries to container hosts file (--add-host)
You can add other hosts into a container's `/etc/hosts` file by using one or
more `--add-host` flags. This example adds a static address for a host named
`docker`:
```bash
$ docker run --add-host=docker:10.180.0.1 --rm -it debian
root@f38c87f2a42d:/# ping docker
PING docker (10.180.0.1): 48 data bytes
56 bytes from 10.180.0.1: icmp_seq=0 ttl=254 time=7.600 ms
56 bytes from 10.180.0.1: icmp_seq=1 ttl=254 time=30.705 ms
^C--- docker ping statistics ---
2 packets transmitted, 2 packets received, 0% packet loss
round-trip min/avg/max/stddev = 7.600/19.152/30.705/11.553 ms
```
Sometimes you need to connect to the Docker host from within your
container. To enable this, pass the Docker host's IP address to
the container using the `--add-host` flag. To find the host's address,
use the `ip addr show` command.
The flags you pass to `ip addr show` depend on whether you are
using IPv4 or IPv6 networking in your containers. Use the following
flags for IPv4 address retrieval for a network device named `eth0`:
```bash
$ HOSTIP=`ip -4 addr show scope global dev eth0 | grep inet | awk '{print \$2}' | cut -d / -f 1`
$ docker run --add-host=docker:${HOSTIP} --rm -it debian
```
For IPv6 use the `-6` flag instead of the `-4` flag. For other network
devices, replace `eth0` with the correct device name (for example `docker0`
for the bridge device).
### Set ulimits in container (--ulimit)
Since setting `ulimit` settings in a container requires extra privileges not
available in the default container, you can set these using the `--ulimit` flag.
`--ulimit` is specified with a soft and hard limit as such:
`<type>=<soft limit>[:<hard limit>]`, for example:
```bash
$ docker run --ulimit nofile=1024:1024 --rm debian sh -c "ulimit -n"
1024
```
> **Note**: If you do not provide a `hard limit`, the `soft limit` will be used
> for both values. If no `ulimits` are set, they will be inherited from
> the default `ulimits` set on the daemon. `as` option is disabled now.
> In other words, the following script is not supported:
>
> ```bash
> $ docker run -it --ulimit as=1024 fedora /bin/bash`
> ```
The values are sent to the appropriate `syscall` as they are set.
Docker doesn't perform any byte conversion. Take this into account when setting the values.
#### For `nproc` usage
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 example, start four
containers with `daemon` user:
```bash
$ docker run -d -u daemon --ulimit nproc=3 busybox top
$ docker run -d -u daemon --ulimit nproc=3 busybox top
$ docker run -d -u daemon --ulimit nproc=3 busybox top
$ docker run -d -u daemon --ulimit nproc=3 busybox top
```
The 4th container fails and reports "[8] System error: resource temporarily unavailable" error.
This fails because the caller set `nproc=3` resulting in the first three containers using up
the three processes quota set for the `daemon` user.
### Stop container with signal (--stop-signal)
The `--stop-signal` flag sets the system call signal that will be sent to the container to exit.
This signal can be a valid unsigned number that matches a position in the kernel's syscall table, for instance 9,
or a signal name in the format SIGNAME, for instance SIGKILL.
### Optional security options (--security-opt)
On Windows, this flag can be used to specify the `credentialspec` option.
The `credentialspec` must be in the format `file://spec.txt` or `registry://keyname`.
### Stop container with timeout (--stop-timeout)
The `--stop-timeout` flag sets the timeout (in seconds) that a pre-defined (see `--stop-signal`) system call
signal that will be sent to the container to exit. After timeout elapses the container will be killed with SIGKILL.
### Specify isolation technology for container (--isolation)
This option is useful in situations where you are running Docker containers on
Windows. The `--isolation <value>` option sets a container's isolation technology.
On Linux, the only supported is the `default` option which uses
Linux namespaces. These two commands are equivalent on Linux:
```bash
$ docker run -d busybox top
$ docker run -d --isolation default busybox top
```
On Windows, `--isolation` can take one of these values:
| Value | Description |
|:----------|:------------------------------------------------------------------------------------------------------------------|
| `default` | Use the value specified by the Docker daemon's `--exec-opt` or system default (see below). |
| `process` | Shared-kernel namespace isolation (not supported on Windows client operating systems older than Windows 10 1809). |
| `hyperv` | Hyper-V hypervisor partition-based isolation. |
The default isolation on Windows server operating systems is `process`. The default
isolation on Windows client operating systems is `hyperv`. An attempt to start a container on a client
operating system older than Windows 10 1809 with `--isolation process` will fail.
On Windows server, assuming the default configuration, these commands are equivalent
and result in `process` isolation:
```powershell
PS C:\> docker run -d microsoft/nanoserver powershell echo process
PS C:\> docker run -d --isolation default microsoft/nanoserver powershell echo process
PS C:\> docker run -d --isolation process microsoft/nanoserver powershell echo process
```
If you have set the `--exec-opt isolation=hyperv` option on the Docker `daemon`, or
are running against a Windows client-based daemon, these commands are equivalent and
result in `hyperv` isolation:
```powershell
PS C:\> docker run -d microsoft/nanoserver powershell echo hyperv
PS C:\> docker run -d --isolation default microsoft/nanoserver powershell echo hyperv
PS C:\> docker run -d --isolation hyperv microsoft/nanoserver powershell echo hyperv
```
### Specify hard limits on memory available to containers (-m, --memory)
These parameters always set an upper limit on the memory available to the container. On Linux, this
is set on the cgroup and applications in a container can query it at `/sys/fs/cgroup/memory/memory.limit_in_bytes`.
On Windows, this will affect containers differently depending on what type of isolation is used.
- With `process` isolation, Windows will report the full memory of the host system, not the limit to applications running inside the container
```powershell
PS C:\> docker run -it -m 2GB --isolation=process microsoft/nanoserver powershell Get-ComputerInfo *memory*
CsTotalPhysicalMemory : 17064509440
CsPhyicallyInstalledMemory : 16777216
OsTotalVisibleMemorySize : 16664560
OsFreePhysicalMemory : 14646720
OsTotalVirtualMemorySize : 19154928
OsFreeVirtualMemory : 17197440
OsInUseVirtualMemory : 1957488
OsMaxProcessMemorySize : 137438953344
```
- With `hyperv` isolation, Windows will create a utility VM that is big enough to hold the memory limit, plus the minimal OS needed to host the container. That size is reported as "Total Physical Memory."
```powershell
PS C:\> docker run -it -m 2GB --isolation=hyperv microsoft/nanoserver powershell Get-ComputerInfo *memory*
CsTotalPhysicalMemory : 2683355136
CsPhyicallyInstalledMemory :
OsTotalVisibleMemorySize : 2620464
OsFreePhysicalMemory : 2306552
OsTotalVirtualMemorySize : 2620464
OsFreeVirtualMemory : 2356692
OsInUseVirtualMemory : 263772
OsMaxProcessMemorySize : 137438953344
```
### Configure namespaced kernel parameters (sysctls) at runtime
The `--sysctl` sets namespaced kernel parameters (sysctls) in the
container. For example, to turn on IP forwarding in the containers
network namespace, run this command:
```bash
$ docker run --sysctl net.ipv4.ip_forward=1 someimage
```
> **Note**: Not all sysctls are namespaced. Docker does not support changing sysctls
> inside of a container that also modify the host system. As the kernel
> evolves we expect to see more sysctls become namespaced.
#### Currently supported sysctls
- `IPC Namespace`:
```none
kernel.msgmax, kernel.msgmnb, kernel.msgmni, kernel.sem, kernel.shmall, kernel.shmmax, kernel.shmmni, kernel.shm_rmid_forced
Sysctls beginning with fs.mqueue.*
```
If you use the `--ipc=host` option these sysctls will not be allowed.
- `Network Namespace`:
Sysctls beginning with net.*
If you use the `--network=host` option using these sysctls will not be allowed.
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