1. Create a logs folder in the forum folder and give the application pool identity write access to it.

2. In the web.config of the forum, set stdoutLogEnabled to true:

   <aspNetCore processPath="dotnet" arguments=".\YAF.dll" stdoutLogEnabled="true" stdoutLogFile=".\logs\stdout" hostingModel="inprocess" />

3. Open the forum again and look at the newest file in logs.

Turn the log off again when you are done. It isn't rotated and grows without limit.

See also Troubleshoot ASP.NET Core on IIS.

• Check ConnectionStrings:DefaultConnection and that BoardConfiguration:ConnectionProviderName matches your database, see BoardConfiguration Settings.
• SQL Server: add TrustServerCertificate=True; to the connection string if the server doesn't have a trusted certificate. The connection is encrypted by default.
• SQL Server with Integrated Security=True under IIS: the forum connects as the application pool identity (e.g. IIS APPPOOL\YourAppPool). That login needs access to the database.
• SQLite: the forum user needs write access to the database file and its folder.

ASP.NET Core can't store its data protection keys, so they are lost on every restart.

• IIS: in the advanced settings of the application pool, set Load User Profile to True.
• Linux: the user the forum runs as needs a home folder, see Hosting on Linux with nginx.
• Docker: the keys are stored inside the container and are lost when it is recreated, e.g. after an update. Users have to log in again after updates.

The rate limiter blocked the requests. Either RateLimiterPermitLimit is too low (use at least 100), or all users share the address of a reverse proxy, see Reverse proxy and Cloudflare.

The forum runs behind a reverse proxy or CDN that isn't trusted, see Reverse proxy and Cloudflare.

The forum runs behind a proxy that handles HTTPS, see Reverse proxy and Cloudflare - HTTPS at the proxy.

• Check the MailConfiguration section in appsettings.json (Host, Port, UserName, Password).
• Send a test email from Admin > Mail with Send Test.
• Errors when sending mails are written to the Event Log.

They use SignalR with WebSockets. The proxy has to forward the Upgrade and Connection headers, see the nginx configuration in Hosting on Linux with nginx. Under IIS, install the WebSocket Protocol feature.

Check the Max File Size in the host settings, and the upload limit of your proxy (nginx: client_max_body_size, default 1 MB).

For example:

Lock obtain timed out: SharingNativeFSLock@/var/www/yafnet/wwwroot/Search_Data/write.lock:
System.IO.IOException: Cannot create directory: /var/www/yafnet/wwwroot/Search_Data
---> System.UnauthorizedAccessException: Access to the path '/var/www/yafnet/wwwroot/Search_Data' is denied.

The forum user can't write to the forum folder. unzip applies the permissions stored in the zip file, which can be missing write access, and chown alone doesn't change them. Fix the owner and the permissions, then restart the forum:

sudo chown -R yafnet:yafnet /var/www/yafnet
sudo chmod -R u+rwX,go+rX,go-w /var/www/yafnet
sudo systemctl restart yafnet

Do this after every update as well, see Hosting on Linux with nginx.

File names on Linux are case-sensitive. The folders must be named wwwroot/images and wwwroot/uploads.

Ask in the YAF.NET support forum. Include the YAF.NET version, the database, the hosting (IIS, Linux, Docker) and the error message from the logs.