140 lines
4.7 KiB
Markdown
140 lines
4.7 KiB
Markdown
---
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description: Using tmpfs mounts
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title: Use tmpfs mounts
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keywords: storage, persistence, data persistence, tmpfs
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redirect_from:
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- /engine/admin/volumes/tmpfs/
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---
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[Volumes](volumes.md) and [bind mounts](bind-mounts.md) let you share files
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between the host machine and container so that you can persist data even after
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the container is stopped.
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If you're running Docker on Linux, you have a third option: `tmpfs` mounts.
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When you create a container with a `tmpfs` mount, the container can create
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files outside the container's writable layer.
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As opposed to volumes and bind mounts, a `tmpfs` mount is temporary, and only
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persisted in the host memory. When the container stops, the `tmpfs` mount is
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removed, and files written there won't be persisted.
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![tmpfs on the Docker host](images/types-of-mounts-tmpfs.png)
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This is useful to temporarily store sensitive files that you don't want to
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persist in either the host or the container writable layer.
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## Limitations of tmpfs mounts
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* Unlike volumes and bind mounts, you can't share `tmpfs` mounts between
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containers.
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* This functionality is only available if you're running Docker on Linux.
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## Choose the --tmpfs or --mount flag
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In general, `--mount` is more explicit and verbose. The biggest difference is
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that the `--tmpfs` flag does not support any configurable options.
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- **`--tmpfs`**: Mounts a `tmpfs` mount without allowing you to specify any
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configurable options, and can only be used with standalone containers.
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- **`--mount`**: Consists of multiple key-value pairs, separated by commas and each
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consisting of a `<key>=<value>` tuple. The `--mount` syntax is more verbose
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than `--tmpfs`:
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- The `type` of the mount, which can be [`bind`](bind-mounts.md), `volume`, or
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[`tmpfs`](tmpfs.md). This topic discusses `tmpfs`, so the type is always
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`tmpfs`.
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- The `destination` takes as its value the path where the `tmpfs` mount
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is mounted in the container. May be specified as `destination`, `dst`,
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or `target`.
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- The `tmpfs-size` and `tmpfs-mode` options. See
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[tmpfs options](#specify-tmpfs-options).
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The examples below show both the `--mount` and `--tmpfs` syntax where possible,
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and `--mount` is presented first.
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### Differences between `--tmpfs` and `--mount` behavior
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- The `--tmpfs` flag does not allow you to specify any configurable options.
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- The `--tmpfs` flag cannot be used with swarm services. You must use `--mount`.
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## Use a tmpfs mount in a container
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To use a `tmpfs` mount in a container, use the `--tmpfs` flag, or use the
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`--mount` flag with `type=tmpfs` and `destination` options. There is no
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`source` for `tmpfs` mounts. The following example creates a `tmpfs` mount at
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`/app` in a Nginx container. The first example uses the `--mount` flag and the
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second uses the `--tmpfs` flag.
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<ul class="nav nav-tabs">
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<li class="active"><a data-toggle="tab" data-group="mount" data-target="#mount-run"><code>--mount</code></a></li>
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<li><a data-toggle="tab" data-group="volume" data-target="#tmpfs-run"><code>--tmpfs</code></a></li>
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</ul>
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<div class="tab-content">
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<div id="mount-run" class="tab-pane fade in active" markdown="1">
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```bash
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$ docker run -d \
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-it \
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--name tmptest \
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--mount type=tmpfs,destination=/app \
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nginx:latest
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```
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</div><!--mount-->
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<div id="tmpfs-run" class="tab-pane fade" markdown="1">
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```bash
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$ docker run -d \
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-it \
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--name tmptest \
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--tmpfs /app \
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nginx:latest
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```
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</div><!--volume-->
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</div><!--tab-content-->
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Verify that the mount is a `tmpfs` mount by running `docker container inspect
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tmptest` and looking for the `Mounts` section:
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```json
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"Tmpfs": {
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"/app": ""
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},
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```
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Remove the container:
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```bash
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$ docker container stop tmptest
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$ docker container rm tmptest
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```
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### Specify tmpfs options
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`tmpfs` mounts allow for two configuration options, neither of which is
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required. If you need to specify these options, you must use the `--mount` flag,
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as the `--tmpfs` flag does not support them.
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| Option | Description |
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|:-------------|:------------------------------------------------------------------------------------------------------|
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| `tmpfs-size` | Size of the tmpfs mount in bytes. Unlimited by default. |
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| `tmpfs-mode` | File mode of the tmpfs in octal. For instance, `700` or `0770`. Defaults to `1777` or world-writable. |
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The following example sets the `tmpfs-mode` to `1770`, so that it is not
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world-readable within the container.
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```bash
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docker run -d \
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-it \
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--name tmptest \
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--mount type=tmpfs,destination=/app,tmpfs-mode=1770 \
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nginx:latest
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```
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## Next steps
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- Learn about [volumes](volumes.md)
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- Learn about [bind mounts](bind-mounts.md)
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- Learn about [storage drivers](/storage/storagedriver/) |