Using tmpfs Mounts in Docker

--- description: Using tmpfs mounts title: tmpfs mounts weight: 30 keywords: storage, persistence, data persistence, tmpfs aliases: - /engine/admin/volumes/tmpfs/ - /storage/tmpfs/ --- [Volumes](volumes.md) and [bind mounts](bind-mounts.md) let you share files between the host machine and container so that you can persist data even after the container is stopped. If you're running Docker on Linux, you have a third option: tmpfs mounts. When you create a container with a tmpfs mount, the container can create files outside the container's writable layer. As opposed to volumes and bind mounts, a tmpfs mount is temporary, and only persisted in the host memory. When the container stops, the tmpfs mount is removed, and files written there won't be persisted. tmpfs mounts are best used for cases when you do not want the data to persist either on the host machine or within the container. This may be for security reasons or to protect the performance of the container when your application needs to write a large volume of non-persistent state data. > [!IMPORTANT] > tmpfs mounts in Docker map directly to > [tmpfs](https://en.wikipedia.org/wiki/Tmpfs) in the Linux kernel. As such, > the temporary data may be written to a swap file, and thereby persisted to > the filesystem. ## Mounting over existing data If you create a tmpfs mount into a directory in the container in which files or directories exist, the pre-existing files are obscured by the mount. This is similar to if you were to save files into `/mnt` on a Linux host, and then mounted a USB drive into `/mnt`. The contents of `/mnt` would be obscured by the contents of the USB drive until the USB drive was unmounted. With containers, there's no straightforward way of removing a mount to reveal the obscured files again. Your best option is to recreate the container without the mount. ## Limitations of tmpfs mounts - Unlike volumes and bind mounts, you can't share tmpfs mounts between containers. - This functionality is only available if you're running Docker on Linux. - Setting permissions on tmpfs may cause them to [reset after container restart](https://github.com/docker/for-linux/issues/138). In some cases [setting the uid/gid](https://github.com/docker/compose/issues/3425#issuecomment-423091370) can serve as a workaround. ## Syntax To mount a tmpfs with the `docker run` command, you can use either the `--mount` or `--tmpfs` flag. ```console $ docker run --mount type=tmpfs,dst=<mount-path> $ docker run --tmpfs <mount-path> ``` In general, `--mount` is preferred. The main difference is that the `--mount` flag is more explicit. On the other hand, `--tmpfs` is less verbose and gives you more flexibility as it lets you set more mount options. The `--tmpfs` flag cannot be used with swarm services. You must use `--mount`. ### Options for --tmpfs The `--tmpfs` flag consists of two fields, separated by a colon character (`:`). ```console $ docker run --tmpfs <mount-path>[:opts] ``` The first field is the container path to mount into a tmpfs. The second field is optional and lets you set mount options. Valid mount options for `--tmpfs` include: | Option | Description | | ------------ | ------------------------------------------------------------------------------------------- | | `ro` | Creates a read-only tmpfs mount. | | `rw` | Creates a read-write tmpfs mount (default behavior). | | `nosuid` | Prevents `setuid` and `setgid` bits from being honored during execution. | | `suid` | Allows `setuid` and `setgid` bits to be honored during execution (default behavior). | | `nodev` | Device files can be created but are not functional (access results in an error). | | `dev` | Device files can be created and are fully functional. |

This section describes tmpfs mounts in Docker, which are temporary storage locations in the host's memory, unlike volumes and bind mounts that persist data. Tmpfs mounts are useful for storing non-persistent data for security or performance reasons. It details how to use the `--mount` or `--tmpfs` flags with `docker run` to create tmpfs mounts, highlighting the differences and options available for each.