# Running containers

# Running containers

> Running and configuring containers with the Docker CLI

# Running containers

   Table of contents

---

Docker runs processes in isolated containers. A container is a process
which runs on a host. The host may be local or remote. When you
execute `docker run`, the container process that runs is isolated in
that it has its own file system, its own networking, and its own
isolated process tree separate from the host.

This page details how to use the `docker run` command to run containers.

## General form

A `docker run` command takes the following form:

```console
$ docker run [OPTIONS] IMAGE[:TAG|@DIGEST] [COMMAND] [ARG...]
```

The `docker run` command must specify an [image reference](#image-references)
to create the container from.

### Image references

The image reference is the name and version of the image. You can use the image
reference to create or run a container based on an image.

- `docker run IMAGE[:TAG][@DIGEST]`
- `docker create IMAGE[:TAG][@DIGEST]`

An image tag is the image version, which defaults to `latest` when omitted. Use
the tag to run a container from specific version of an image. For example, to
run version `24.04` of the `ubuntu` image: `docker run ubuntu:24.04`.

#### Image digests

Images using the v2 or later image format have a content-addressable identifier
called a digest. As long as the input used to generate the image is unchanged,
the digest value is predictable.

The following example runs a container from the `alpine` image with the
`sha256:9cacb71397b640eca97488cf08582ae4e4068513101088e9f96c9814bfda95e0` digest:

```console
$ docker run alpine@sha256:9cacb71397b640eca97488cf08582ae4e4068513101088e9f96c9814bfda95e0 date
```

### Options

`[OPTIONS]` let you configure options for the container. For example, you can
give the container a name (`--name`), or run it as a background process (`-d`).
You can also set options to control things like resource constraints and
networking.

### Commands and arguments

You can use the `[COMMAND]` and `[ARG...]` positional arguments to specify
commands and arguments for the container to run when it starts up. For example,
you can specify `sh` as the `[COMMAND]`, combined with the `-i` and `-t` flags,
to start an interactive shell in the container (if the image you select has an
`sh` executable on `PATH`).

```console
$ docker run -it IMAGE sh
```

> Note
>
> Depending on your Docker system configuration, you may be
> required to preface the `docker run` command with `sudo`. To avoid
> having to use `sudo` with the `docker` command, your system
> administrator can create a Unix group called `docker` and add users to
> it. For more information about this configuration, refer to the Docker
> installation documentation for your operating system.

## Foreground and background

When you start a container, the container runs in the foreground by default.
If you want to run the container in the background instead, you can use the
`--detach` (or `-d`) flag. This starts the container without occupying your
terminal window.

```console
$ docker run -d IMAGE
```

While the container runs in the background, you can interact with the container
using other CLI commands. For example, `docker logs` lets you view the logs for
the container, and `docker attach` brings it to the foreground.

```console
$ docker run -d nginx
0246aa4d1448a401cabd2ce8f242192b6e7af721527e48a810463366c7ff54f1
$ docker ps
CONTAINER ID   IMAGE     COMMAND                  CREATED         STATUS        PORTS     NAMES
0246aa4d1448   nginx     "/docker-entrypoint.…"   2 seconds ago   Up 1 second   80/tcp    pedantic_liskov
$ docker logs -n 5 0246aa4d1448
2023/11/06 15:58:23 [notice] 1#1: start worker process 33
2023/11/06 15:58:23 [notice] 1#1: start worker process 34
2023/11/06 15:58:23 [notice] 1#1: start worker process 35
2023/11/06 15:58:23 [notice] 1#1: start worker process 36
2023/11/06 15:58:23 [notice] 1#1: start worker process 37
$ docker attach 0246aa4d1448
^C
2023/11/06 15:58:40 [notice] 1#1: signal 2 (SIGINT) received, exiting
...
```

For more information about `docker run` flags related to foreground and
background modes, see:

- [docker run --detach](https://docs.docker.com/reference/cli/docker/container/run/#detach): run container in background
- [docker run --attach](https://docs.docker.com/reference/cli/docker/container/run/#attach): attach to `stdin`, `stdout`, and `stderr`
- [docker run --tty](https://docs.docker.com/reference/cli/docker/container/run/#tty): allocate a pseudo-tty
- [docker run --interactive](https://docs.docker.com/reference/cli/docker/container/run/#interactive): keep `stdin` open even if not attached

For more information about re-attaching to a background container, see
[docker attach](https://docs.docker.com/reference/cli/docker/container/attach/).

## Container identification

You can identify a container in three ways:

| Identifier type | Example value |
| --- | --- |
| UUID long identifier | f78375b1c487e03c9438c729345e54db9d20cfa2ac1fc3494b6eb60872e74778 |
| UUID short identifier | f78375b1c487 |
| Name | evil_ptolemy |

The UUID identifier is a random ID assigned to the container by the daemon.

The daemon generates a random string name for containers automatically. You can
also define a custom name using [the--nameflag](https://docs.docker.com/reference/cli/docker/container/run/#name).
Defining a `name` can be a handy way to add meaning to a container. If you
specify a `name`, you can use it when referring to the container in a
user-defined network. This works for both background and foreground Docker
containers.

A container identifier is not the same thing as an image reference. The image
reference specifies which image to use when you run a container. You can't run
`docker exec nginx:alpine sh` to open a shell in a container based on the
`nginx:alpine` image, because `docker exec` expects a container identifier
(name or ID), not an image.

While the image used by a container is not an identifier for the container, you
find out the IDs of containers using an image by using the `--filter` flag. For
example, the following `docker ps` command gets the IDs of all running
containers based on the `nginx:alpine` image:

```console
$ docker ps -q --filter ancestor=nginx:alpine
```

For more information about using filters, see
[Filtering](https://docs.docker.com/config/filter/).

## Container networking

Containers have networking enabled by default, and they can make outgoing
connections. If you're running multiple containers that need to communicate
with each other, you can create a custom network and attach the containers to
the network.

When multiple containers are attached to the same custom network, they can
communicate with each other using the container names as a DNS hostname. The
following example creates a custom network named `my-net`, and runs two
containers that attach to the network.

```console
$ docker network create my-net
$ docker run -d --name web --network my-net nginx:alpine
$ docker run --rm -it --network my-net busybox
/ # ping web
PING web (172.18.0.2): 56 data bytes
64 bytes from 172.18.0.2: seq=0 ttl=64 time=0.326 ms
64 bytes from 172.18.0.2: seq=1 ttl=64 time=0.257 ms
64 bytes from 172.18.0.2: seq=2 ttl=64 time=0.281 ms
^C
--- web ping statistics ---
3 packets transmitted, 3 packets received, 0% packet loss
round-trip min/avg/max = 0.257/0.288/0.326 ms
```

For more information about container networking, see [Networking
overview](https://docs.docker.com/network/)

## Filesystem mounts

By default, the data in a container is stored in an ephemeral, writable
container layer. Removing the container also removes its data. If you want to
use persistent data with containers, you can use filesystem mounts to store the
data persistently on the host system. Filesystem mounts can also let you share
data between containers and the host.

Docker supports two main categories of mounts:

- Volume mounts
- Bind mounts

Volume mounts are great for persistently storing data for containers, and for
sharing data between containers. Bind mounts, on the other hand, are for
sharing data between a container and the host.

You can add a filesystem mount to a container using the `--mount` flag for the
`docker run` command.

The following sections show basic examples of how to create volumes and bind
mounts. For more in-depth examples and descriptions, refer to the section of
the [storage section](https://docs.docker.com/storage/) in the documentation.

### Volume mounts

To create a volume mount:

```console
$ docker run --mount source=VOLUME_NAME,target=[PATH] [IMAGE] [COMMAND...]
```

The `--mount` flag takes two parameters in this case: `source` and `target`.
The value for the `source` parameter is the name of the volume. The value of
`target` is the mount location of the volume inside the container. Once you've
created the volume, any data you write to the volume is persisted, even if you
stop or remove the container:

```console
$ docker run --rm --mount source=my_volume,target=/foo busybox \
  echo "hello, volume!" > /foo/hello.txt
$ docker run --mount source=my_volume,target=/bar busybox
  cat /bar/hello.txt
hello, volume!
```

The `target` must always be an absolute path, such as `/src/docs`. An absolute
path starts with a `/` (forward slash). Volume names must start with an
alphanumeric character, followed by `a-z0-9`, `_` (underscore), `.` (period) or
`-` (hyphen).

### Bind mounts

To create a bind mount:

```console
$ docker run -it --mount type=bind,source=[PATH],target=[PATH] busybox
```

In this case, the `--mount` flag takes three parameters. A type (`bind`), and
two paths. The `source` path is the location on the host that you want to
bind mount into the container. The `target` path is the mount destination
inside the container.

Bind mounts are read-write by default, meaning that you can both read and write
files to and from the mounted location from the container. Changes that you
make, such as adding or editing files, are reflected on the host filesystem:

```console
$ docker run -it --mount type=bind,source=.,target=/foo busybox
/ # echo "hello from container" > /foo/hello.txt
/ # exit
$ cat hello.txt
hello from container
```

## Exit status

The exit code from `docker run` gives information about why the container
failed to run or why it exited. The following sections describe the meanings of
different container exit codes values.

### 125

Exit code `125` indicates that the error is with Docker daemon itself.

```console
$ docker run --foo busybox; echo $?

flag provided but not defined: --foo
See 'docker run --help'.
125
```

### 126

Exit code `126` indicates that the specified contained command can't be invoked.
The container command in the following example is: `/etc`.

```console
$ docker run busybox /etc; echo $?

docker: Error response from daemon: Container command '/etc' could not be invoked.
126
```

### 127

Exit code `127` indicates that the contained command can't be found.

```console
$ docker run busybox foo; echo $?

docker: Error response from daemon: Container command 'foo' not found or does not exist.
127
```

### Other exit codes

Any exit code other than `125`, `126`, and `127` represent the exit code of the
provided container command.

```console
$ docker run busybox /bin/sh -c 'exit 3'
$ echo $?
3
```

## Runtime constraints on resources

The operator can also adjust the performance parameters of the
container:

| Option | Description |
| --- | --- |
| -m,--memory="" | Memory limit (format:<number>[<unit>]). Number is a positive integer. Unit can be one ofb,k,m, org. Minimum is 6M. |
| --memory-swap="" | Total memory limit (memory + swap, format:<number>[<unit>]). Number is a positive integer. Unit can be one ofb,k,m, org. |
| --memory-reservation="" | Memory soft limit (format:<number>[<unit>]). Number is a positive integer. Unit can be one ofb,k,m, org. |
| --kernel-memory="" | Kernel memory limit (format:<number>[<unit>]). Number is a positive integer. Unit can be one ofb,k,m, org. Minimum is 4M. |
| -c,--cpu-shares=0 | CPU shares (relative weight) |
| --cpus=0.000 | Number of CPUs. Number is a fractional number. 0.000 means no limit. |
| --cpu-period=0 | Limit the CPU CFS (Completely Fair Scheduler) period |
| --cpuset-cpus="" | CPUs in which to allow execution (0-3, 0,1) |
| --cpuset-mems="" | Memory nodes (MEMs) in which to allow execution (0-3, 0,1). Only effective on NUMA systems. |
| --cpu-quota=0 | Limit the CPU CFS (Completely Fair Scheduler) quota |
| --cpu-rt-period=0 | Limit the CPU real-time period. In microseconds. Requires parent cgroups be set and cannot be higher than parent. Also check rtprio ulimits. |
| --cpu-rt-runtime=0 | Limit the CPU real-time runtime. In microseconds. Requires parent cgroups be set and cannot be higher than parent. Also check rtprio ulimits. |
| --blkio-weight=0 | Block IO weight (relative weight) accepts a weight value between 10 and 1000. |
| --blkio-weight-device="" | Block IO weight (relative device weight, format:DEVICE_NAME:WEIGHT) |
| --device-read-bps="" | Limit read rate from a device (format:<device-path>:<number>[<unit>]). Number is a positive integer. Unit can be one ofkb,mb, orgb. |
| --device-write-bps="" | Limit write rate to a device (format:<device-path>:<number>[<unit>]). Number is a positive integer. Unit can be one ofkb,mb, orgb. |
| --device-read-iops="" | Limit read rate (IO per second) from a device (format:<device-path>:<number>). Number is a positive integer. |
| --device-write-iops="" | Limit write rate (IO per second) to a device (format:<device-path>:<number>). Number is a positive integer. |
| --oom-kill-disable=false | Whether to disable OOM Killer for the container or not. |
| --oom-score-adj=0 | Tune container's OOM preferences (-1000 to 1000) |
| --memory-swappiness="" | Tune a container's memory swappiness behavior. Accepts an integer between 0 and 100. |
| --shm-size="" | Size of/dev/shm. The format is<number><unit>.numbermust be greater than0. Unit is optional and can beb(bytes),k(kilobytes),m(megabytes), org(gigabytes). If you omit the unit, the system uses bytes. If you omit the size entirely, the system uses64m. |

### User memory constraints

We have four ways to set user memory usage:

| Option | Result |
| --- | --- |
| memory=inf, memory-swap=inf(default) | There is no memory limit for the container. The container can use
as much memory as needed. |
| memory=L<inf, memory-swap=inf | (specify memory and set memory-swap as-1) The container is
not allowed to use more than L bytes of memory, but can use as much swap
as is needed (if the host supports swap memory). |
| memory=L<inf, memory-swap=2*L | (specify memory without memory-swap) The container is not allowed to
use more than L bytes of memory, swapplusmemory usage is double
of that. |
| memory=L<inf, memory-swap=S<inf, L<=S | (specify both memory and memory-swap) The container is not allowed to
use more than L bytes of memory, swapplusmemory usage is limited
by S. |

Examples:

```console
$ docker run -it ubuntu:24.04 /bin/bash
```

We set nothing about memory, this means the processes in the container can use
as much memory and swap memory as they need.

```console
$ docker run -it -m 300M --memory-swap -1 ubuntu:24.04 /bin/bash
```

We set memory limit and disabled swap memory limit, this means the processes in
the container can use 300M memory and as much swap memory as they need (if the
host supports swap memory).

```console
$ docker run -it -m 300M ubuntu:24.04 /bin/bash
```

We set memory limit only, this means the processes in the container can use
300M memory and 300M swap memory, by default, the total virtual memory size
(`--memory-swap`) will be set as double of memory, in this case, memory + swap
would be 2*300M, so processes can use 300M swap memory as well.

```console
$ docker run -it -m 300M --memory-swap 1G ubuntu:24.04 /bin/bash
```

We set both memory and swap memory, so the processes in the container can use
300M memory and 700M swap memory.

Memory reservation is a kind of memory soft limit that allows for greater
sharing of memory. Under normal circumstances, containers can use as much of
the memory as needed and are constrained only by the hard limits set with the
`-m`/`--memory` option. When memory reservation is set, Docker detects memory
contention or low memory and forces containers to restrict their consumption to
a reservation limit.

Always set the memory reservation value below the hard limit, otherwise the hard
limit takes precedence. A reservation of 0 is the same as setting no
reservation. By default (without reservation set), memory reservation is the
same as the hard memory limit.

Memory reservation is a soft-limit feature and does not guarantee the limit
won't be exceeded. Instead, the feature attempts to ensure that, when memory is
heavily contended for, memory is allocated based on the reservation hints/setup.

The following example limits the memory (`-m`) to 500M and sets the memory
reservation to 200M.

```console
$ docker run -it -m 500M --memory-reservation 200M ubuntu:24.04 /bin/bash
```

Under this configuration, when the container consumes memory more than 200M and
less than 500M, the next system memory reclaim attempts to shrink container
memory below 200M.

The following example set memory reservation to 1G without a hard memory limit.

```console
$ docker run -it --memory-reservation 1G ubuntu:24.04 /bin/bash
```

The container can use as much memory as it needs. The memory reservation setting
ensures the container doesn't consume too much memory for long time, because
every memory reclaim shrinks the container's consumption to the reservation.

By default, kernel kills processes in a container if an out-of-memory (OOM)
error occurs. To change this behaviour, use the `--oom-kill-disable` option.
Only disable the OOM killer on containers where you have also set the
`-m/--memory` option. If the `-m` flag is not set, this can result in the host
running out of memory and require killing the host's system processes to free
memory.

The following example limits the memory to 100M and disables the OOM killer for
this container:

```console
$ docker run -it -m 100M --oom-kill-disable ubuntu:24.04 /bin/bash
```

The following example, illustrates a dangerous way to use the flag:

```console
$ docker run -it --oom-kill-disable ubuntu:24.04 /bin/bash
```

The container has unlimited memory which can cause the host to run out memory
and require killing system processes to free memory. The `--oom-score-adj`
parameter can be changed to select the priority of which containers will
be killed when the system is out of memory, with negative scores making them
less likely to be killed, and positive scores more likely.

### Kernel memory constraints

Kernel memory is fundamentally different than user memory as kernel memory can't
be swapped out. The inability to swap makes it possible for the container to
block system services by consuming too much kernel memory. Kernel memory includes：

- stack pages
- slab pages
- sockets memory pressure
- tcp memory pressure

You can setup kernel memory limit to constrain these kinds of memory. For example,
every process consumes some stack pages. By limiting kernel memory, you can
prevent new processes from being created when the kernel memory usage is too high.

Kernel memory is never completely independent of user memory. Instead, you limit
kernel memory in the context of the user memory limit. Assume "U" is the user memory
limit and "K" the kernel limit. There are three possible ways to set limits:

| Option | Result |
| --- | --- |
| U != 0, K = inf(default) | This is the standard memory limitation mechanism already present before using
kernel memory. Kernel memory is completely ignored. |
| U != 0, K < U | Kernel memory is a subset of the user memory. This setup is useful in
deployments where the total amount of memory per-cgroup is overcommitted.
Overcommitting kernel memory limits is definitely not recommended, since the
box can still run out of non-reclaimable memory.
In this case, you can configure K so that the sum of all groups is
never greater than the total memory. Then, freely set U at the expense of
the system's service quality. |
| U != 0, K > U | Since kernel memory charges are also fed to the user counter and reclamation
is triggered for the container for both kinds of memory. This configuration
gives the admin a unified view of memory. It is also useful for people
who just want to track kernel memory usage. |

Examples:

```console
$ docker run -it -m 500M --kernel-memory 50M ubuntu:24.04 /bin/bash
```

We set memory and kernel memory, so the processes in the container can use
500M memory in total, in this 500M memory, it can be 50M kernel memory tops.

```console
$ docker run -it --kernel-memory 50M ubuntu:24.04 /bin/bash
```

We set kernel memory without **-m**, so the processes in the container can
use as much memory as they want, but they can only use 50M kernel memory.

### Swappiness constraint

By default, a container's kernel can swap out a percentage of anonymous pages.
To set this percentage for a container, specify a `--memory-swappiness` value
between 0 and 100. A value of 0 turns off anonymous page swapping. A value of
100 sets all anonymous pages as swappable. By default, if you are not using
`--memory-swappiness`, memory swappiness value will be inherited from the parent.

For example, you can set:

```console
$ docker run -it --memory-swappiness=0 ubuntu:24.04 /bin/bash
```

Setting the `--memory-swappiness` option is helpful when you want to retain the
container's working set and to avoid swapping performance penalties.

### CPU share constraint

By default, all containers get the same proportion of CPU cycles. This proportion
can be modified by changing the container's CPU share weighting relative
to the weighting of all other running containers.

To modify the proportion from the default of 1024, use the `-c` or `--cpu-shares`
flag to set the weighting to 2 or higher. If 0 is set, the system will ignore the
value and use the default of 1024.

The proportion will only apply when CPU-intensive processes are running.
When tasks in one container are idle, other containers can use the
left-over CPU time. The actual amount of CPU time will vary depending on
the number of containers running on the system.

For example, consider three containers, one has a cpu-share of 1024 and
two others have a cpu-share setting of 512. When processes in all three
containers attempt to use 100% of CPU, the first container would receive
50% of the total CPU time. If you add a fourth container with a cpu-share
of 1024, the first container only gets 33% of the CPU. The remaining containers
receive 16.5%, 16.5% and 33% of the CPU.

On a multi-core system, the shares of CPU time are distributed over all CPU
cores. Even if a container is limited to less than 100% of CPU time, it can
use 100% of each individual CPU core.

For example, consider a system with more than three cores. If you start one
container `{C0}` with `-c=512` running one process, and another container
`{C1}` with `-c=1024` running two processes, this can result in the following
division of CPU shares:

```
PID    container	CPU	CPU share
100    {C0}		0	100% of CPU0
101    {C1}		1	100% of CPU1
102    {C1}		2	100% of CPU2
```

### CPU period constraint

The default CPU CFS (Completely Fair Scheduler) period is 100ms. We can use
`--cpu-period` to set the period of CPUs to limit the container's CPU usage.
And usually `--cpu-period` should work with `--cpu-quota`.

Examples:

```console
$ docker run -it --cpu-period=50000 --cpu-quota=25000 ubuntu:24.04 /bin/bash
```

If there is 1 CPU, this means the container can get 50% CPU worth of run-time every 50ms.

In addition to use `--cpu-period` and `--cpu-quota` for setting CPU period constraints,
it is possible to specify `--cpus` with a float number to achieve the same purpose.
For example, if there is 1 CPU, then `--cpus=0.5` will achieve the same result as
setting `--cpu-period=50000` and `--cpu-quota=25000` (50% CPU).

The default value for `--cpus` is `0.000`, which means there is no limit.

For more information, see the [CFS documentation on bandwidth limiting](https://www.kernel.org/doc/Documentation/scheduler/sched-bwc.txt).

### Cpuset constraint

We can set cpus in which to allow execution for containers.

Examples:

```console
$ docker run -it --cpuset-cpus="1,3" ubuntu:24.04 /bin/bash
```

This means processes in container can be executed on cpu 1 and cpu 3.

```console
$ docker run -it --cpuset-cpus="0-2" ubuntu:24.04 /bin/bash
```

This means processes in container can be executed on cpu 0, cpu 1 and cpu 2.

We can set mems in which to allow execution for containers. Only effective
on NUMA systems.

Examples:

```console
$ docker run -it --cpuset-mems="1,3" ubuntu:24.04 /bin/bash
```

This example restricts the processes in the container to only use memory from
memory nodes 1 and 3.

```console
$ docker run -it --cpuset-mems="0-2" ubuntu:24.04 /bin/bash
```

This example restricts the processes in the container to only use memory from
memory nodes 0, 1 and 2.

### CPU quota constraint

The `--cpu-quota` flag limits the container's CPU usage. The default 0 value
allows the container to take 100% of a CPU resource (1 CPU). The CFS (Completely Fair
Scheduler) handles resource allocation for executing processes and is default
Linux Scheduler used by the kernel. Set this value to 50000 to limit the container
to 50% of a CPU resource. For multiple CPUs, adjust the `--cpu-quota` as necessary.
For more information, see the [CFS documentation on bandwidth limiting](https://www.kernel.org/doc/Documentation/scheduler/sched-bwc.txt).

### Block IO bandwidth (Blkio) constraint

By default, all containers get the same proportion of block IO bandwidth
(blkio). This proportion is 500. To modify this proportion, change the
container's blkio weight relative to the weighting of all other running
containers using the `--blkio-weight` flag.

> Note
>
> The blkio weight setting is only available for direct IO. Buffered IO is not
> currently supported.

The `--blkio-weight` flag can set the weighting to a value between 10 to 1000.
For example, the commands below create two containers with different blkio
weight:

```console
$ docker run -it --name c1 --blkio-weight 300 ubuntu:24.04 /bin/bash
$ docker run -it --name c2 --blkio-weight 600 ubuntu:24.04 /bin/bash
```

If you do block IO in the two containers at the same time, by, for example:

```console
$ time dd if=/mnt/zerofile of=test.out bs=1M count=1024 oflag=direct
```

You'll find that the proportion of time is the same as the proportion of blkio
weights of the two containers.

The `--blkio-weight-device="DEVICE_NAME:WEIGHT"` flag sets a specific device weight.
The `DEVICE_NAME:WEIGHT` is a string containing a colon-separated device name and weight.
For example, to set `/dev/sda` device weight to `200`:

```console
$ docker run -it \
    --blkio-weight-device "/dev/sda:200" \
    ubuntu
```

If you specify both the `--blkio-weight` and `--blkio-weight-device`, Docker
uses the `--blkio-weight` as the default weight and uses `--blkio-weight-device`
to override this default with a new value on a specific device.
The following example uses a default weight of `300` and overrides this default
on `/dev/sda` setting that weight to `200`:

```console
$ docker run -it \
    --blkio-weight 300 \
    --blkio-weight-device "/dev/sda:200" \
    ubuntu
```

The `--device-read-bps` flag limits the read rate (bytes per second) from a device.
For example, this command creates a container and limits the read rate to `1mb`
per second from `/dev/sda`:

```console
$ docker run -it --device-read-bps /dev/sda:1mb ubuntu
```

The `--device-write-bps` flag limits the write rate (bytes per second) to a device.
For example, this command creates a container and limits the write rate to `1mb`
per second for `/dev/sda`:

```console
$ docker run -it --device-write-bps /dev/sda:1mb ubuntu
```

Both flags take limits in the `<device-path>:<limit>[unit]` format. Both read
and write rates must be a positive integer. You can specify the rate in `kb`
(kilobytes), `mb` (megabytes), or `gb` (gigabytes).

The `--device-read-iops` flag limits read rate (IO per second) from a device.
For example, this command creates a container and limits the read rate to
`1000` IO per second from `/dev/sda`:

```console
$ docker run -it --device-read-iops /dev/sda:1000 ubuntu
```

The `--device-write-iops` flag limits write rate (IO per second) to a device.
For example, this command creates a container and limits the write rate to
`1000` IO per second to `/dev/sda`:

```console
$ docker run -it --device-write-iops /dev/sda:1000 ubuntu
```

Both flags take limits in the `<device-path>:<limit>` format. Both read and
write rates must be a positive integer.

## Additional groups

```console
--group-add: Add additional groups to run as
```

By default, the docker container process runs with the supplementary groups looked
up for the specified user. If one wants to add more to that list of groups, then
one can use this flag:

```console
$ docker run --rm --group-add audio --group-add nogroup --group-add 777 busybox id

uid=0(root) gid=0(root) groups=10(wheel),29(audio),99(nogroup),777
```

## Runtime privilege and Linux capabilities

| Option | Description |
| --- | --- |
| --cap-add | Add Linux capabilities |
| --cap-drop | Drop Linux capabilities |
| --privileged | Give extended privileges to this container |
| --device=[] | Allows you to run devices inside the container without the--privilegedflag. |

By default, Docker containers are "unprivileged" and cannot, for
example, run a Docker daemon inside a Docker container. This is because
by default a container is not allowed to access any devices, but a
"privileged" container is given access to all devices (see
the documentation on [cgroups devices](https://www.kernel.org/doc/Documentation/cgroup-v1/devices.txt)).

The `--privileged` flag gives all capabilities to the container. When the operator
executes `docker run --privileged`, Docker enables access to all devices on
the host, and reconfigures AppArmor or SELinux to allow the container
nearly all the same access to the host as processes running outside
containers on the host. Use this flag with caution.
For more information about the `--privileged` flag, see the
[docker runreference](https://docs.docker.com/reference/cli/docker/container/run/#privileged).

If you want to limit access to a specific device or devices you can use
the `--device` flag. It allows you to specify one or more devices that
will be accessible within the container.

```console
$ docker run --device=/dev/snd:/dev/snd ...
```

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:

```console
$ 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:w --rm -it ubuntu fdisk  /dev/xvdc
    crash....

$ docker run --device=/dev/sda:/dev/xvdc:m --rm -it ubuntu fdisk  /dev/xvdc
fdisk: unable to open /dev/xvdc: Operation not permitted
```

In addition to `--privileged`, the operator can have fine grain control over the
capabilities using `--cap-add` and `--cap-drop`. By default, Docker has a default
list of capabilities that are kept. The following table lists the Linux capability
options which are allowed by default and can be dropped.

| Capability Key | Capability Description |
| --- | --- |
| AUDIT_WRITE | Write records to kernel auditing log. |
| CHOWN | Make arbitrary changes to file UIDs and GIDs (see chown(2)). |
| DAC_OVERRIDE | Bypass file read, write, and execute permission checks. |
| FOWNER | Bypass permission checks on operations that normally require the file system UID of the process to match the UID of the file. |
| FSETID | Don't clear set-user-ID and set-group-ID permission bits when a file is modified. |
| KILL | Bypass permission checks for sending signals. |
| MKNOD | Create special files using mknod(2). |
| NET_BIND_SERVICE | Bind a socket to internet domain privileged ports (port numbers less than 1024). |
| NET_RAW | Use RAW and PACKET sockets. |
| SETFCAP | Set file capabilities. |
| SETGID | Make arbitrary manipulations of process GIDs and supplementary GID list. |
| SETPCAP | Modify process capabilities. |
| SETUID | Make arbitrary manipulations of process UIDs. |
| SYS_CHROOT | Use chroot(2), change root directory. |

The next table shows the capabilities which are not granted by default and may be added.

| Capability Key | Capability Description |
| --- | --- |
| AUDIT_CONTROL | Enable and disable kernel auditing; change auditing filter rules; retrieve auditing status and filtering rules. |
| AUDIT_READ | Allow reading the audit log via multicast netlink socket. |
| BLOCK_SUSPEND | Allow preventing system suspends. |
| BPF | Allow creating BPF maps, loading BPF Type Format (BTF) data, retrieve JITed code of BPF programs, and more. |
| CHECKPOINT_RESTORE | Allow checkpoint/restore related operations. Introduced in kernel 5.9. |
| DAC_READ_SEARCH | Bypass file read permission checks and directory read and execute permission checks. |
| IPC_LOCK | Lock memory (mlock(2), mlockall(2), mmap(2), shmctl(2)). |
| IPC_OWNER | Bypass permission checks for operations on System V IPC objects. |
| LEASE | Establish leases on arbitrary files (see fcntl(2)). |
| LINUX_IMMUTABLE | Set the FS_APPEND_FL and FS_IMMUTABLE_FL i-node flags. |
| MAC_ADMIN | Allow MAC configuration or state changes. Implemented for the Smack LSM. |
| MAC_OVERRIDE | Override Mandatory Access Control (MAC). Implemented for the Smack Linux Security Module (LSM). |
| NET_ADMIN | Perform various network-related operations. |
| NET_BROADCAST | Make socket broadcasts, and listen to multicasts. |
| PERFMON | Allow system performance and observability privileged operations using perf_events, i915_perf and other kernel subsystems |
| SYS_ADMIN | Perform a range of system administration operations. |
| SYS_BOOT | Use reboot(2) and kexec_load(2), reboot and load a new kernel for later execution. |
| SYS_MODULE | Load and unload kernel modules. |
| SYS_NICE | Raise process nice value (nice(2), setpriority(2)) and change the nice value for arbitrary processes. |
| SYS_PACCT | Use acct(2), switch process accounting on or off. |
| SYS_PTRACE | Trace arbitrary processes using ptrace(2). |
| SYS_RAWIO | Perform I/O port operations (iopl(2) and ioperm(2)). |
| SYS_RESOURCE | Override resource Limits. |
| SYS_TIME | Set system clock (settimeofday(2), stime(2), adjtimex(2)); set real-time (hardware) clock. |
| SYS_TTY_CONFIG | Use vhangup(2); employ various privileged ioctl(2) operations on virtual terminals. |
| SYSLOG | Perform privileged syslog(2) operations. |
| WAKE_ALARM | Trigger something that will wake up the system. |

Further reference information is available on the [capabilities(7) - Linux man page](https://man7.org/linux/man-pages/man7/capabilities.7.html),
and in the [Linux kernel source code](https://github.com/torvalds/linux/blob/124ea650d3072b005457faed69909221c2905a1f/include/uapi/linux/capability.h).

Both flags support the value `ALL`, so to allow a container to use all capabilities
except for `MKNOD`:

```console
$ docker run --cap-add=ALL --cap-drop=MKNOD ...
```

The `--cap-add` and `--cap-drop` flags accept capabilities to be specified with
a `CAP_` prefix. The following examples are therefore equivalent:

```console
$ docker run --cap-add=SYS_ADMIN ...
$ docker run --cap-add=CAP_SYS_ADMIN ...
```

For interacting with the network stack, instead of using `--privileged` they
should use `--cap-add=NET_ADMIN` to modify the network interfaces.

```console
$ docker run -it --rm  ubuntu:24.04 ip link add dummy0 type dummy

RTNETLINK answers: Operation not permitted

$ docker run -it --rm --cap-add=NET_ADMIN ubuntu:24.04 ip link add dummy0 type dummy
```

To mount a FUSE based filesystem, you need to combine both `--cap-add` and
`--device`:

```console
$ docker run --rm -it --cap-add SYS_ADMIN sshfs sshfs sven@10.10.10.20:/home/sven /mnt

fuse: failed to open /dev/fuse: Operation not permitted

$ docker run --rm -it --device /dev/fuse sshfs sshfs sven@10.10.10.20:/home/sven /mnt

fusermount: mount failed: Operation not permitted

$ docker run --rm -it --cap-add SYS_ADMIN --device /dev/fuse sshfs

# sshfs sven@10.10.10.20:/home/sven /mnt
The authenticity of host '10.10.10.20 (10.10.10.20)' can't be established.
ECDSA key fingerprint is 25:34:85:75:25:b0:17:46:05:19:04:93:b5:dd:5f:c6.
Are you sure you want to continue connecting (yes/no)? yes
sven@10.10.10.20's password:

root@30aa0cfaf1b5:/# ls -la /mnt/src/docker

total 1516
drwxrwxr-x 1 1000 1000   4096 Dec  4 06:08 .
drwxrwxr-x 1 1000 1000   4096 Dec  4 11:46 ..
-rw-rw-r-- 1 1000 1000     16 Oct  8 00:09 .dockerignore
-rwxrwxr-x 1 1000 1000    464 Oct  8 00:09 .drone.yml
drwxrwxr-x 1 1000 1000   4096 Dec  4 06:11 .git
-rw-rw-r-- 1 1000 1000    461 Dec  4 06:08 .gitignore
....
```

The default seccomp profile will adjust to the selected capabilities, in order to allow
use of facilities allowed by the capabilities, so you should not have to adjust this.

## Overriding image defaults

When you build an image from a [Dockerfile](https://docs.docker.com/reference/dockerfile/),
or when committing it, you can set a number of default parameters that take
effect when the image starts up as a container. When you run an image, you can
override those defaults using flags for the `docker run` command.

- [Default entrypoint](#default-entrypoint)
- [Default command and options](#default-command-and-options)
- [Expose ports](#exposed-ports)
- [Environment variables](#environment-variables)
- [Healthcheck](#healthchecks)
- [User](#user)
- [Working directory](#working-directory)

### Default command and options

The command syntax for `docker run` supports optionally specifying commands and
arguments to the container's entrypoint, represented as `[COMMAND]` and
`[ARG...]` in the following synopsis example:

```console
$ docker run [OPTIONS] IMAGE[:TAG|@DIGEST] [COMMAND] [ARG...]
```

This command is optional because whoever created the `IMAGE` may have already
provided a default `COMMAND`, using the Dockerfile `CMD` instruction. When you
run a container, you can override that `CMD` instruction just by specifying a
new `COMMAND`.

If the image also specifies an `ENTRYPOINT` then the `CMD` or `COMMAND`
get appended as arguments to the `ENTRYPOINT`.

### Default entrypoint

```text
--entrypoint="": Overwrite the default entrypoint set by the image
```

The entrypoint refers to the default executable that's invoked when you run a
container. A container's entrypoint is defined using the Dockerfile
`ENTRYPOINT` instruction. It's similar to specifying a default command because
it specifies, but the difference is that you need to pass an explicit flag to
override the entrypoint, whereas you can override default commands with
positional arguments. The defines a container's default behavior, with the idea
that when you set an entrypoint you can run the container *as if it were that
binary*, complete with default options, and you can pass in more options as
commands. But there are cases where you may want to run something else inside
the container. This is when overriding the default entrypoint at runtime comes
in handy, using the `--entrypoint` flag for the `docker run` command.

The `--entrypoint` flag expects a string value, representing the name or path
of the binary that you want to invoke when the container starts. The following
example shows you how to run a Bash shell in a container that has been set up
to automatically run some other binary (like `/usr/bin/redis-server`):

```console
$ docker run -it --entrypoint /bin/bash example/redis
```

The following examples show how to pass additional parameters to the custom
entrypoint, using the positional command arguments:

```console
$ docker run -it --entrypoint /bin/bash example/redis -c ls -l
$ docker run -it --entrypoint /usr/bin/redis-cli example/redis --help
```

You can reset a containers entrypoint by passing an empty string, for example:

```console
$ docker run -it --entrypoint="" mysql bash
```

> Note
>
> Passing `--entrypoint` clears out any default command set on the image. That
> is, any `CMD` instruction in the Dockerfile used to build it.

### Exposed ports

By default, when you run a container, none of the container's ports are exposed
to the host. This means you won't be able to access any ports that the
container might be listening on. To make a container's ports accessible from
the host, you need to publish the ports.

You can start the container with the `-P` or `-p` flags to expose its ports:

- The `-P` (or `--publish-all`) flag publishes all the exposed ports to the
  host. Docker binds each exposed port to a random port on the host.
  The `-P` flag only publishes port numbers that are explicitly flagged as
  exposed, either using the Dockerfile `EXPOSE` instruction or the `--expose`
  flag for the `docker run` command.
- The `-p` (or `--publish`) flag lets you explicitly map a single port or range
  of ports in the container to the host.

The port number inside the container (where the service listens) doesn't need
to match the port number published on the outside of the container (where
clients connect). For example, inside the container an HTTP service might be
listening on port 80. At runtime, the port might be bound to 42800 on the host.
To find the mapping between the host ports and the exposed ports, use the
`docker port` command.

### Environment variables

Docker automatically sets some environment variables when creating a Linux
container. Docker doesn't set any environment variables when creating a Windows
container.

The following environment variables are set for Linux containers:

| Variable | Value |
| --- | --- |
| HOME | Set based on the value ofUSER |
| HOSTNAME | The hostname associated with the container |
| PATH | Includes popular directories, such as/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin |
| TERM | xtermif the container is allocated a pseudo-TTY |

Additionally, you can set any environment variable in the container by using
one or more `-e` flags. You can even override the variables mentioned above, or
variables defined using a Dockerfile `ENV` instruction when building the image.

If you name an environment variable without specifying a value, the current
value of the named variable on the host is propagated into the container's
environment:

```console
$ export today=Wednesday
$ docker run -e "deep=purple" -e today --rm alpine env

PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
HOSTNAME=d2219b854598
deep=purple
today=Wednesday
HOME=/root
```

```powershell
PS C:\> docker run --rm -e "foo=bar" microsoft/nanoserver cmd /s /c set
ALLUSERSPROFILE=C:\ProgramData
APPDATA=C:\Users\ContainerAdministrator\AppData\Roaming
CommonProgramFiles=C:\Program Files\Common Files
CommonProgramFiles(x86)=C:\Program Files (x86)\Common Files
CommonProgramW6432=C:\Program Files\Common Files
COMPUTERNAME=C2FAEFCC8253
ComSpec=C:\Windows\system32\cmd.exe
foo=bar
LOCALAPPDATA=C:\Users\ContainerAdministrator\AppData\Local
NUMBER_OF_PROCESSORS=8
OS=Windows_NT
Path=C:\Windows\system32;C:\Windows;C:\Windows\System32\Wbem;C:\Windows\System32\WindowsPowerShell\v1.0\;C:\Users\ContainerAdministrator\AppData\Local\Microsoft\WindowsApps
PATHEXT=.COM;.EXE;.BAT;.CMD
PROCESSOR_ARCHITECTURE=AMD64
PROCESSOR_IDENTIFIER=Intel64 Family 6 Model 62 Stepping 4, GenuineIntel
PROCESSOR_LEVEL=6
PROCESSOR_REVISION=3e04
ProgramData=C:\ProgramData
ProgramFiles=C:\Program Files
ProgramFiles(x86)=C:\Program Files (x86)
ProgramW6432=C:\Program Files
PROMPT=$P$G
PUBLIC=C:\Users\Public
SystemDrive=C:
SystemRoot=C:\Windows
TEMP=C:\Users\ContainerAdministrator\AppData\Local\Temp
TMP=C:\Users\ContainerAdministrator\AppData\Local\Temp
USERDOMAIN=User Manager
USERNAME=ContainerAdministrator
USERPROFILE=C:\Users\ContainerAdministrator
windir=C:\Windows
```

### Healthchecks

The following flags for the `docker run` command let you control the parameters
for container healthchecks:

| Option | Description |
| --- | --- |
| --health-cmd | Command to run to check health |
| --health-interval | Time between running the check |
| --health-retries | Consecutive failures needed to report unhealthy |
| --health-timeout | Maximum time to allow one check to run |
| --health-start-period | Start period for the container to initialize before starting health-retries countdown |
| --health-start-interval | Time between running the check during the start period |
| --no-healthcheck | Disable any container-specifiedHEALTHCHECK |

Example:

```console
$ docker run --name=test -d \
    --health-cmd='stat /etc/passwd || exit 1' \
    --health-interval=2s \
    busybox sleep 1d
$ sleep 2; docker inspect --format='{{.State.Health.Status}}' test
healthy
$ docker exec test rm /etc/passwd
$ sleep 2; docker inspect --format='{{json .State.Health}}' test
{
  "Status": "unhealthy",
  "FailingStreak": 3,
  "Log": [
    {
      "Start": "2016-05-25T17:22:04.635478668Z",
      "End": "2016-05-25T17:22:04.7272552Z",
      "ExitCode": 0,
      "Output": "  File: /etc/passwd\n  Size: 334       \tBlocks: 8          IO Block: 4096   regular file\nDevice: 32h/50d\tInode: 12          Links: 1\nAccess: (0664/-rw-rw-r--)  Uid: (    0/    root)   Gid: (    0/    root)\nAccess: 2015-12-05 22:05:32.000000000\nModify: 2015..."
    },
    {
      "Start": "2016-05-25T17:22:06.732900633Z",
      "End": "2016-05-25T17:22:06.822168935Z",
      "ExitCode": 0,
      "Output": "  File: /etc/passwd\n  Size: 334       \tBlocks: 8          IO Block: 4096   regular file\nDevice: 32h/50d\tInode: 12          Links: 1\nAccess: (0664/-rw-rw-r--)  Uid: (    0/    root)   Gid: (    0/    root)\nAccess: 2015-12-05 22:05:32.000000000\nModify: 2015..."
    },
    {
      "Start": "2016-05-25T17:22:08.823956535Z",
      "End": "2016-05-25T17:22:08.897359124Z",
      "ExitCode": 1,
      "Output": "stat: can't stat '/etc/passwd': No such file or directory\n"
    },
    {
      "Start": "2016-05-25T17:22:10.898802931Z",
      "End": "2016-05-25T17:22:10.969631866Z",
      "ExitCode": 1,
      "Output": "stat: can't stat '/etc/passwd': No such file or directory\n"
    },
    {
      "Start": "2016-05-25T17:22:12.971033523Z",
      "End": "2016-05-25T17:22:13.082015516Z",
      "ExitCode": 1,
      "Output": "stat: can't stat '/etc/passwd': No such file or directory\n"
    }
  ]
}
```

The health status is also displayed in the `docker ps` output.

### User

The default user within a container is `root` (uid = 0). You can set a default
user to run the first process with the Dockerfile `USER` instruction. When
starting a container, you can override the `USER` instruction by passing the
`-u` option.

```text
-u="", --user="": Sets the username or UID used and optionally the groupname or GID for the specified command.
```

The followings examples are all valid:

```text
--user=[ user | user:group | uid | uid:gid | user:gid | uid:group ]
```

> Note
>
> If you pass a numeric user ID, it must be in the range of 0-2147483647. If
> you pass a username, the user must exist in the container.

### Working directory

The default working directory for running binaries within a container is the
root directory (`/`). The default working directory of an image is set using
the Dockerfile `WORKDIR` command. You can override the default working
directory for an image using the `-w` (or `--workdir`) flag for the `docker run` command:

```text
$ docker run --rm -w /my/workdir alpine pwd
/my/workdir
```

If the directory doesn't already exist in the container, it's created.
