TechnitiumSoftware/DnsServer · error · Exception

The 'connectionString' parameter must not define 'Initial Ca

Error message

The 'connectionString' parameter must not define 'Initial Catalog'. Configure the 'databaseName' parameter above instead.

What it means

QueryLogsSqlServerApp separates server coordinates ('connectionString') from the target schema ('databaseName'). SQL Server uses 'Initial Catalog' to denote the database, and this guard rejects any connectionString containing that keyword (case-insensitive). The app supplies the database itself, so a user-supplied Initial Catalog would conflict.

Source

Thrown at Apps/QueryLogsSqlServerApp/App.cs:372

                if (config is null)
                    throw new InvalidOperationException();

                using JsonDocument jsonDocument = JsonDocument.Parse(config, _jsonParseOptions);
                JsonElement jsonConfig = jsonDocument.RootElement;

                bool enableLogging = jsonConfig.GetPropertyValue("enableLogging", false);
                int maxQueueSize = jsonConfig.GetPropertyValue("maxQueueSize", 1000000);
                _maxLogDays = jsonConfig.GetPropertyValue("maxLogDays", 0);
                _maxLogRecords = jsonConfig.GetPropertyValue("maxLogRecords", 0);
                _databaseName = jsonConfig.GetPropertyValue("databaseName", "DnsQueryLogs");
                _connectionString = jsonConfig.GetPropertyValue("connectionString", null);

                if (_connectionString is null)
                    throw new Exception("Please specify a valid connection string in 'connectionString' parameter.");

                if (_connectionString.Contains("Initial Catalog", StringComparison.OrdinalIgnoreCase))
                    throw new Exception("The 'connectionString' parameter must not define 'Initial Catalog'. Configure the 'databaseName' parameter above instead.");

                if (!_connectionString.TrimEnd().EndsWith(';'))
                    _connectionString += ";";

                async Task ApplyConfig()
                {
                    if (enableLogging)
                    {
                        await using (SqlConnection connection = new SqlConnection(_connectionString))
                        {
                            await connection.OpenAsync();

                            await using (SqlCommand command = connection.CreateCommand())
                            {
                                command.CommandText = @$"
IF NOT EXISTS(SELECT * FROM sys.databases WHERE name = '{_databaseName}')
BEGIN
    CREATE DATABASE ""{_databaseName}"";

View on GitHub (pinned to d0484b6c1e)

Solutions

Remove the 'Initial Catalog=...' pair from 'connectionString', keeping Server/Auth/Encrypt options.
Set the schema via the 'databaseName' parameter (default 'DnsQueryLogs').
Verify no 'Initial Catalog' substring remains before saving.

Example fix

// before
"connectionString": "Server=localhost;Initial Catalog=DnsQueryLogs;User Id=sa;Password=pass;"

// after
"connectionString": "Server=localhost;User Id=sa;Password=pass;TrustServerCertificate=true;",
"databaseName": "DnsQueryLogs"

Defensive patterns

Strategy: validation

Validate before calling

static void ValidateSqlServerConnectionString(string cs)
{
    if (cs.Contains("Initial Catalog", StringComparison.OrdinalIgnoreCase))
        throw new InvalidOperationException(
            "connectionString must not contain 'Initial Catalog'. Use the databaseName parameter.");
}

ValidateSqlServerConnectionString(connectionString);

Prevention

Remember SQL Server uses 'Initial Catalog' where MySQL/Postgres use 'Database'.
Remove Initial Catalog from any pasted connection string before saving.
Maintain per-backend config lint rules.

When it happens

Trigger: ApplyConfig gets a 'connectionString' that includes 'Initial Catalog=...' (any casing). The case-insensitive Contains match throws. Note: unlike the MySQL/Postgres checks, this one does NOT strip spaces, so 'InitialCatalog' is caught but oddly-spaced variants behave per the literal substring.

Common situations: Pasting a SQL Server connection string from SSMS, connectionstrings.com, or EF Core that baked 'Initial Catalog' into it, into the dnsApp.config without removing that keyword.

Related errors

AI-assisted analysis of TechnitiumSoftware/DnsServer@d0484b6c1e (2026-08-13). Data as JSON: /api/errors/a1b5515c6f336e13. Report an issue: GitHub.