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# Common issues

### Loading...

Often if the application is misconfigured the `Loading...` dialog is continuously displayed. This is most likely caused by the backed failing to start. The Maintenance -> Logs section should give you more details on what's happening. If there is no exception, check the Portainer log, or start the container in the foreground (without the `-d` parameter) to observe any exceptions. It's advisable to enable `trace` or `debug`. Check the Debug tips on detailed instructions.

### Incorrect SCAN_SUBNETS

One of the most common issues is not configuring `SCAN_SUBNETS` correctly. If this setting is misconfigured you will only see one or two devices in your devices list after a scan. Please read the subnets docs carefully to resolve this.

### Duplicate devices and notifications

The app uses the MAC address as an unique identifier for devices. If a new MAC is detected a new device is added to the application and corresponding notifications are triggered. This means that if the MAC of an existing device changes, the device will be logged as a new device. You can usually prevent this from happening by changing the device configuration (in Android, iOS, or Windows) for your network. See the Random Macs guide for details.

### Permissions

Make sure you File permissions are set correctly.

- If facing issues (AJAX errors, can't write to DB, empty screen, etc,) make sure permissions are set correctly, and check the logs under `/app/log`.
- To solve permission issues you can try setting the owner and group of the `app.db` by executing the following on the host system: `docker exec netalertx chown -R www-data:www-data /app/db/app.db`.
- If still facing issues, try to map the app.db file (⚠ not folder) to `:/app/db/app.db` (see docker-compose Examples for details)

### Container restarts / crashes

- Check the logs for details. Often a required setting for a notification method is missing.

### unable to resolve host

- Check that your `SCAN_SUBNETS` variable is using the correct mask and `--interface`. See the subnets docs for details.

### Invalid JSON

Check the Invalid JSON errors debug help docs on how to proceed.

### sudo execution failing (e.g.: on arpscan) on a Raspberry Pi 4

> sudo: unexpected child termination condition: 0

Resolution based on this issue

    wget ftp.us.debian.org/debian/pool/main/libs/libseccomp/libseccomp2_2.5.3-2_armhf.deb
    sudo dpkg -i libseccomp2_2.5.3-2_armhf.deb

The link above will probably break in time too. Go to https://packages.debian.org/sid/armhf/libseccomp2/download to find the new version number and put that in the url.

### Only Router and own device show up

Make sure that the subnet and interface in `SCAN_SUBNETS` are correct. If your device/NAS has multiple ethernet ports, you probably need to change `eth0` to something else.

### Losing my settings and devices after an update

If you lose your devices and/or settings after an update that means you don't have the `/app/db` and `/app/config` folders mapped to a permanent storage. That means every time you update these folders are re-created. Make sure you have the volumes specified correctly in your `docker-compose.yml` or run command.

### The application is slow

Slowness is usually caused by incorrect settings (the app might restart, so check the `app.log`), too many background processes (disable unnecessary scanners), too long scans (limit the number of scanned devices), too many disk operations, or some maintenance plugins might have failed. See the Performance tips docs for details.