switch nextcloud from sqlite to mysql

docs/repair-nextcloud.md

@@ -0,0 +1,46 @@
+# Repairing Nextcloud
+
+You can run the maintenance commands like this:
+
+```
+sudo -u nextcloud nextcloud-occ maintenance:mode --on
+sudo -u nextcloud nextcloud-occ maintenance:repair
+sudo -u nextcloud nextcloud-occ maintenance:mode --off
+```
+
+Converting from SQLite to MySQL (mariadb)
+
+First: keep Nextcloud set to SQLite as its dbtype, and separately launch MySQL
+as a service by copying the configuration found
+[here](https://github.com/NixOS/nixpkgs/blob/nixos-unstable/nixos/modules/services/web-apps/nextcloud.nix).
+
+No password is necessary, since the user-based auth works with UNIX sockets.
+
+You can connect to the MySQL instance like this:
+
+```
+sudo -u nextcloud mysql -S /run/mysqld/mysqld.sock
+```
+
+Create a blank database for Nextcloud:
+
+```sql
+create database nextcloud;
+```
+
+Now setup the [conversion](https://docs.nextcloud.com/server/17/admin_manual/configuration_database/db_conversion.html):
+
+```
+sudo -u nextcloud nextcloud-occ db:convert-type mysql nextcloud localhost nextcloud
+```
+
+Ignore the password prompt. Proceed with the conversion.
+
+Now `config.php` will be updated but the override config from NixOS will not
+be. Now update your NixOS configuration:
+
+- Remove the `mysql` service you created.
+- Set `dbtype` to `mysql`.
+- Set `database.createLocally` to `true`.
+
+Rebuild your configuration.