parameters (sysctls) at runtime](/reference/cli/docker/container/run.md#sysctl).

### `tmpfs`

`tmpfs` mounts a temporary file system inside the container. It can be a single value or a list.

```yml
tmpfs:
 - <path>
 - <path>:<options>
```

- `path`: The path inside the container where the tmpfs will be mounted.
- `options`: Comma-separated list of options for the tmpfs mount.

Available options:

- `mode`: Sets the file system permissions.
- `uid`: Sets the user ID that owns the mounted tmpfs.
- `gid`: Sets the group ID that owns the mounted tmpfs.

```yml
services:
  app:
    tmpfs:
      - /data:mode=755,uid=1009,gid=1009
      - /run
```

### `tty`

`tty` configures a service's container to run with a TTY. This is the same as running a container with the 
`-t` or `--tty` flag. For more information, see [Allocate a pseudo-TTY](/reference/cli/docker/container/run.md#tty).

Supported values are `true` or `false`.

### `ulimits`

`ulimits` overrides the default `ulimits` for a container. It's specified either as an integer for a single limit
or as mapping for soft/hard limits.

```yml
ulimits:
  nproc: 65535
  nofile:
    soft: 20000
    hard: 40000
```

### `user`

`user` overrides the user used to run the container process. The default is set by the image, for example Dockerfile `USER`. If it's not set, then `root`.

### `userns_mode`

`userns_mode` sets the user namespace for the service. Supported values are platform specific and may depend
on platform configuration.

```yml
userns_mode: "host"
```

### `uts`

{{< summary-bar feature_name="Compose uts" >}}

`uts` configures the UTS namespace mode set for the service container. When unspecified
it is the runtime's decision to assign a UTS namespace, if supported. Available values are:

- `'host'`: Results in the container using the same UTS namespace as the host.

```yml
    uts: "host"
```

### `volumes`

{{% include "compose/services-volumes.md" %}}

The following example shows a named volume (`db-data`) being used by the `backend` service,
and a bind mount defined for a single service.

```yml
services:
  backend:
    image: example/backend
    volumes:
      - type: volume
        source: db-data
        target: /data
        volume:
          nocopy: true
          subpath: sub
      - type: bind
        source: /var/run/postgres/postgres.sock
        target: /var/run/postgres/postgres.sock

volumes:
  db-data:
```

For more information about the `volumes` top-level element, see [Volumes](volumes.md).

#### Short syntax

The short syntax uses a single string with colon-separated values to specify a volume mount
(`VOLUME:CONTAINER_PATH`), or an access mode (`VOLUME:CONTAINER_PATH:ACCESS_MODE`).

- `VOLUME`: Can be either a host path on the platform hosting containers (bind mount) or a volume name.
- `CONTAINER_PATH`: The path in the container where the volume is mounted.
- `ACCESS_MODE`: A comma-separated `,` list of options:
  - `rw`: Read and write access. This is the default if none is specified.
  - `ro`: Read-only access.
  - `z`: SELinux option indicating that the bind mount host content is shared among multiple containers.
  - `Z`: SELinux option indicating that the bind mount host content is private and unshared for other containers.

> [!NOTE]
>
> The SELinux re-labeling bind mount option is ignored on platforms without SELinux.

> [!NOTE]
> Relative host paths are only supported by Compose that deploy to a
> local container runtime. This is because the relative path is resolved from the Compose file’s parent