DOCS: permissions on Synology

docs/DOCKER_INSTALLATION.md

@@ -51,6 +51,9 @@ See alternative [docker-compose examples](https://docs.netalertx.com/DOCKER_COMP
 
 ### Docker environment variables
 
+> [!NOTE]
+> If you see only 2 devices, you might need to run the container as root by setting a custom `PUID` and `PGID` as some systems don't support `--cap-add` properly, such as some Synology setups. See [running as root](https://docs.netalertx.com/FILE_PERMISSIONS/#running-as-root).
+
 | Variable | Description | Example/Default Value |
 | :------------- |:------------------------| -----:|
 | `PUID`      |Runtime UID override, set to `0` to run as root. |  `20211` |
@@ -127,8 +130,3 @@ You can read or watch several [community configuration guides](https://docs.neta
 
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docs/SYNOLOGY_GUIDE.md

@@ -82,9 +82,18 @@ volumes:
 10. Navigate to `<Synology URL>:20211` (or your custom port).
 11. Read the [Subnets](./SUBNETS.md) and [Plugins](./PLUGINS_OVERVIEW.md) docs to complete your setup.
 
-## Solving permission issues
+## Solving permission issues (2 devices visible)
 
-  See also the [Permission overview guide](./FILE_PERMISSIONS.md).
+Some Synology setups don't support `--cap-add` properly. This usually results in seeing only 2 devices and the following error shows when running `ARPSCAN`:
+
+```bash
+You don't have permission to perform this capture on that device
+(socket: Operation not permitted)
+```
+
+To fix this you might need to set the container as ptiviledged `privileged: true` and run as root by setting a custom `PUID` and `PGID`.
+
+See [running as root](./FILE_PERMISSIONS.md) for more details.
 
 ### Configuring the permissions via SSH