# Force client upgrades

> Ensure that users upgrade their clients correctly.

Ensure that users upgrade their Unity Version Control (UVCS) clients correctly.

The UVCS server can reject clients that are older than the current version of the server.

To force a given build number, add the `ForceBuildNumberMatch` key to your `server.conf` file. This key admits the following values:

| Value      | Description                                                                                                                                                                                                                                  |
| ---------- | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| `true`     | Requires exact build number matching so that any client or server that connects to the server must run exactly the same version.                                                                                                             |
| `false`    | Doesn't require a version match. This is the default value.                                                                                                                                                                                  |
| `<number>` | Rejects any connections from callers that run a version with a build number smaller than the `number`. For example, `<ForceBuildNumberMatch>800</ForceBuildNumberMatch>` means the server accepts any version equal to or larger than `800`. |