---
description: Using bind mounts
title: Use bind mounts
keywords: storage, persistence, data persistence, mounts, bind mounts
redirect_from:
- /engine/admin/volumes/bind-mounts/
---

Bind mounts have been around since the early days of Docker. Bind mounts have
limited functionality compared to [volumes](volumes.md). When you use a bind
mount, a file or directory on the _host machine_ is mounted into a container.
The file or directory is referenced by its absolute path on the host
machine. By contrast, when you use a volume, a new directory is created within
Docker's storage directory on the host machine, and Docker manages that
directory's contents.

The file or directory does not need to exist on the Docker host already. It is
created on demand if it does not yet exist. Bind mounts are very performant, but
they rely on the host machine's filesystem having a specific directory structure
available. If you are developing new Docker applications, consider using
[named volumes](volumes.md) instead. You can't use Docker CLI commands to directly
manage bind mounts.

![bind mounts on the Docker host](images/types-of-mounts-bind.png)

## Choose the -v or --mount flag

In general, `--mount` is more explicit and verbose. The biggest difference is that
the `-v` syntax combines all the options together in one field, while the `--mount`
syntax separates them. Here is a comparison of the syntax for each flag.

> **Tip**: New users should use the `--mount` syntax. Experienced users may
> be more familiar with the `-v` or `--volume` syntax, but are encouraged to
> use `--mount`, because research has shown it to be easier to use.

- **`-v` or `--volume`**: Consists of three fields, separated by colon characters
  (`:`). The fields must be in the correct order, and the meaning of each field
  is not immediately obvious.
  - In the case of bind mounts, the first field is the path to the file or
    directory on the **host machine**.
  - The second field is the path where the file or directory is mounted in
    the container.
  - The third field is optional, and is a comma-separated list of options, such
    as `ro`, `z`, and `Z`. These options
    are discussed below.

- **`--mount`**: Consists of multiple key-value pairs, separated by commas and each
  consisting of a `<key>=<value>` tuple. The `--mount` syntax is more verbose
  than `-v` or `--volume`, but the order of the keys is not significant, and
  the value of the flag is easier to understand.
  - The `type` of the mount, which can be `bind`, `volume`, or `tmpfs`. This
    topic discusses bind mounts, so the type is always `bind`.
  - The `source` of the mount. For bind mounts, this is the path to the file
    or directory on the Docker daemon host. May be specified as `source` or
    `src`.
  - The `destination` takes as its value the path where the file or directory
    is mounted in the container. May be specified as `destination`, `dst`,
    or `target`.
  - The `readonly` option, if present, causes the bind mount to be [mounted into
    the container as read-only](#use-a-read-only-bind-mount).
  - The `bind-propagation` option, if present, changes the
    [bind propagation](#configure-bind-propagation). May be one of `rprivate`,
    `private`, `rshared`, `shared`, `rslave`, `slave`.
  - The `--mount` flag does not support `z` or `Z` options for modifying
    selinux labels.

The examples below show both the `--mount` and `-v` syntax where possible, and
`--mount` is presented first.

### Differences between `-v` and `--mount` behavior

Because the `-v` and `--volume` flags have been a part of Docker for a long
time, their behavior cannot be changed. This means that **there is one behavior
that is different between `-v` and `--mount`.**

If you use `-v` or `--volume` to bind-mount a file or directory that does not
yet exist on the Docker host, `-v` creates the endpoint for you. **It is
always created as a directory.**

If you use `--mount` to bind-mount a file or directory that does not
yet exist on the Docker host, Docker does **not** automatically create it for
you, but generates an error.

## Start a container with a bind mount

Consider a case where you have a directory `source` and that when you build the
source code, the artifacts are saved into another directory, `source/target/`.
You want the artifacts to be available to the container at `/app/`, and you
want the container to get access to a new build each time you build the source
on your development host. Use the following command to bind-mount the `target/`
directory into your container at `/app/`. Run the command from within the
`source` directory. The `$(pwd)` sub-command expands to the current working
directory on Linux or macOS hosts.

The `--mount` and `-v` examples below produce the same result. You
can't run them both unless you remove the `devtest` container after running the
first one.

<ul class="nav nav-tabs">
  <li class="active"><a data-toggle="tab" data-group="mount" data-target="#mount-run"><code>--mount</code></a></li>
  <li><a data-toggle="tab" data-group="volume" data-target="#v-run"><code>-v</code></a></li>
</ul>
<div class="tab-content">
<div id="mount-run" class="tab-pane fade in active" markdown="1">

```bash
$ docker run -d \
  -it \
  --name devtest \
  --mount type=bind,source="$(pwd)"/target,target=/app \
  nginx:latest
```

</div><!--mount-->
<div id="v-run" class="tab-pane fade" markdown="1">

```bash
$ docker run -d \
  -it \
  --name devtest \
  -v "$(pwd)"/target:/app \
  nginx:latest
```

</div><!--volume-->
</div><!--tab-content-->

Use `docker inspect devtest` to verify that the bind mount was created
correctly. Look for the `Mounts` section:

```json
"Mounts": [
    {
        "Type": "bind",
        "Source": "/tmp/source/target",
        "Destination": "/app",
        "Mode": "",
        "RW": true,
        "Propagation": "rprivate"
    }
],
```

This shows that the mount is a `bind` mount, it shows the correct source and
destination, it shows that the mount is read-write, and that the propagation is
set to `rprivate`.

Stop the container:

```bash
$ docker container stop devtest

$ docker container rm devtest
```

### Mount into a non-empty directory on the container

If you bind-mount into a non-empty directory on the container, the directory's
existing contents are obscured by the bind mount. This can be beneficial,
such as when you want to test a new version of your application without
building a new image. However, it can also be surprising and this behavior
differs from that of [docker volumes](volumes.md).

This example is contrived to be extreme, but replaces the contents of the
container's `/usr/` directory with the `/tmp/` directory on the host machine. In
most cases, this would result in a non-functioning container.

The `--mount` and `-v` examples have the same end result.

<ul class="nav nav-tabs">
  <li class="active"><a data-toggle="tab" data-group="mount" data-target="#mount-empty-run"><code>--mount</code></a></li>
  <li><a data-toggle="tab" data-group="volume" data-target="#v-empty-run"><code>-v</code></a></li>
</ul>
<div class="tab-content">
<div id="mount-empty-run" class="tab-pane fade in active" markdown="1">

```bash
$ docker run -d \
  -it \
  --name broken-container \
  --mount type=bind,source=/tmp,target=/usr \
  nginx:latest

docker: Error response from daemon: oci runtime error: container_linux.go:262:
starting container process caused "exec: \"nginx\": executable file not found in $PATH".
```

</div><!--mount-->
<div id="v-empty-run" class="tab-pane fade" markdown="1">

```bash
$ docker run -d \
  -it \
  --name broken-container \
  -v /tmp:/usr \
  nginx:latest

docker: Error response from daemon: oci runtime error: container_linux.go:262:
starting container process caused "exec: \"nginx\": executable file not found in $PATH".
```

</div><!--volume-->
</div><!--tab-content-->

The container is created but does not start. Remove it:

```bash
$ docker container rm broken-container
```

## Use a read-only bind mount

For some development applications, the container needs to
write into the bind mount, so changes are propagated back to the
Docker host. At other times, the container only needs read access.

This example modifies the one above but mounts the directory as a read-only
bind mount, by adding `ro` to the (empty by default) list of options, after the
mount point within the container. Where multiple options are present, separate
them by commas.

The `--mount` and `-v` examples have the same result.

<ul class="nav nav-tabs">
  <li class="active"><a data-toggle="tab" data-group="mount" data-target="#mount-readonly"><code>--mount</code></a></li>
  <li><a data-toggle="tab" data-group="volume" data-target="#v-readonly"><code>-v</code></a></li>
</ul>
<div class="tab-content">
<div id="mount-readonly" class="tab-pane fade in active" markdown="1">

```bash
$ docker run -d \
  -it \
  --name devtest \
  --mount type=bind,source="$(pwd)"/target,target=/app,readonly \
  nginx:latest
```

</div><!--mount-->
<div id="v-readonly" class="tab-pane fade" markdown="1">

```bash
$ docker run -d \
  -it \
  --name devtest \
  -v "$(pwd)"/target:/app:ro \
  nginx:latest
```

</div><!--volume-->
</div><!--tab-content-->

Use `docker inspect devtest` to verify that the bind mount was created
correctly. Look for the `Mounts` section:

```json
"Mounts": [
    {
        "Type": "bind",
        "Source": "/tmp/source/target",
        "Destination": "/app",
        "Mode": "ro",
        "RW": false,
        "Propagation": "rprivate"
    }
],
```

Stop the container:

```bash
$ docker container stop devtest

$ docker container rm devtest
```

## Configure bind propagation

Bind propagation defaults to `rprivate` for both bind mounts and volumes. It is
only configurable for bind mounts, and only on Linux host machines. Bind
propagation is an advanced topic and many users never need to configure it.

Bind propagation refers to whether or not mounts created within a given
bind-mount or named volume can be propagated to replicas of that mount. Consider
a mount point `/mnt`, which is also mounted on `/tmp`. The propagation settings
control whether a mount on `/tmp/a` would also be available on `/mnt/a`. Each
propagation setting has a recursive counterpoint. In the case of recursion,
consider that `/tmp/a` is also mounted as `/foo`. The propagation settings
control whether `/mnt/a` and/or `/tmp/a` would exist.

| Propagation setting | Description                                                                                                                                                                                                         |
|:--------------------|:--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| `shared`            | Sub-mounts of the original mount are exposed to replica mounts, and sub-mounts of replica mounts are also propagated to the original mount.                                                                         |
| `slave`             | similar to a shared mount, but only in one direction. If the original mount exposes a sub-mount, the replica mount can see it. However, if the replica mount exposes a sub-mount, the original mount cannot see it. |
| `private`           | The mount is private. Sub-mounts within it are not exposed to replica mounts, and sub-mounts of replica mounts are not exposed to the original mount.                                                               |
| `rshared`           | The same as shared, but the propagation also extends to and from mount points nested within any of the original or replica mount points.                                                                            |
| `rslave`            | The same as slave, but the propagation also extends to and from mount points nested within any of the original or replica mount points.                                                                             |
| `rprivate`          | The default. The same as private, meaning that no mount points anywhere within the original or replica mount points propagate in either direction.                                                                  |

Before you can set bind propagation on a mount point, the host filesystem needs
to already support bind propagation.

For more information about bind propagation, see the
[Linux kernel documentation for shared subtree](https://www.kernel.org/doc/Documentation/filesystems/sharedsubtree.txt){: target="_blank" rel="noopener" class="_"}.

The following example mounts the `target/` directory into the container twice,
and the second mount sets both the `ro` option and the `rslave` bind propagation
option.

The `--mount` and `-v` examples have the same result.

<ul class="nav nav-tabs">
  <li class="active"><a data-toggle="tab" data-group="mount" data-target="#mount-propagation"><code>--mount</code></a></li>
  <li><a data-toggle="tab" data-group="volume" data-target="#v-propagation"><code>-v</code></a></li>
</ul>
<div class="tab-content">
<div id="mount-propagation" class="tab-pane fade in active" markdown="1">

```bash
$ docker run -d \
  -it \
  --name devtest \
  --mount type=bind,source="$(pwd)"/target,target=/app \
  --mount type=bind,source="$(pwd)"/target,target=/app2,readonly,bind-propagation=rslave \
  nginx:latest
```

</div><!--mount-->
<div id="v-propagation" class="tab-pane fade" markdown="1">

```bash
$ docker run -d \
  -it \
  --name devtest \
  -v "$(pwd)"/target:/app \
  -v "$(pwd)"/target:/app2:ro,rslave \
  nginx:latest
```

</div><!--volume-->
</div><!--tab-content-->

Now if you create `/app/foo/`, `/app2/foo/` also exists.

## Configure the selinux label

If you use `selinux` you can add the `z` or `Z` options to modify the selinux
label of the **host file or directory** being mounted into the container. This
affects the file or directory on the host machine itself and can have
consequences outside of the scope of Docker.

- The `z` option indicates that the bind mount content is shared among multiple
  containers.
- The `Z` option indicates that the bind mount content is private and unshared.

Use **extreme** caution with these options. Bind-mounting a system directory
such as `/home` or `/usr` with the `Z` option renders your host machine
inoperable and you may need to relabel the host machine files by hand.

> **Important**: When using bind mounts with services, selinux labels
> (`:Z` and `:z`), as well as `:ro` are ignored. See
> [moby/moby #32579](https://github.com/moby/moby/issues/32579) for details.
{:.important}

This example sets the `z` option to specify that multiple containers can share
the bind mount's contents:

It is not possible to modify the selinux label using the `--mount` flag.

```bash
$ docker run -d \
  -it \
  --name devtest \
  -v "$(pwd)"/target:/app:z \
  nginx:latest
```

## Next steps

- Learn about [volumes](volumes.md).
- Learn about [tmpfs mounts](tmpfs.md).
- Learn about [storage drivers](/storage/storagedriver/).
