# Troubleshooting
URL: https://usememos.com/docs/troubleshooting

Work through the section that matches your symptom. Most problems trace back to ports, file permissions, database connection strings, or proxy headers.

## Port already in use [#port-already-in-use]

Change the port with `--port` or `MEMOS_PORT` and restart the server.

## Cannot write to the data directory [#cannot-write-to-the-data-directory]

Ensure the data directory exists and is writable by the Memos process. You can set it with `--data` or `MEMOS_DATA`.

## Database connection errors [#database-connection-errors]

Verify the driver and DSN:

* `MEMOS_DRIVER` should be `sqlite`, `mysql`, or `postgres`.
* `MEMOS_DSN` should use the correct DSN format for your database.

## Reverse proxy issues [#reverse-proxy-issues]

If you run behind a reverse proxy, make sure:

* `MEMOS_INSTANCE_URL` matches the public URL
* the proxy forwards standard headers (`Host`, `X-Forwarded-*`)

## Docker starts but the app does not respond [#docker-starts-but-the-app-does-not-respond]

Check:

* `docker logs memos`
* whether the host port is already occupied
* whether the mounted data directory is writable

## Attachments are missing after migration [#attachments-are-missing-after-migration]

Confirm which storage backend the instance uses. If attachments are stored outside the database, they must be migrated and backed up separately.

## Still stuck? [#still-stuck]

Check the [FAQ](/docs/faq) or search [GitHub issues](https://github.com/usememos/memos/issues).