louislam/uptime-kuma · critical · Error

Invalid db-config.json, type must be a string

Error message

Invalid db-config.json, type must be a string

What it means

Second guard in readDBConfig(): after confirming dbConfig is an object, it requires dbConfig.type to be a string. Throws when the type field is missing, null, a number, or any non-string value. null and undefined both fail typeof === 'string', so a `{}` or `{ "type": null }` file lands here. This is the most common form of db-config corruption because type is the one mandatory field.

Source

Thrown at server/database.js:216

    /**
     * Read the database config
     * @throws {Error} If the config is invalid
     * @typedef {string|undefined} envString
     * @returns {{type: "sqlite"} | {type:envString, hostname:envString, port:envString, database:envString, username:envString, password:envString, socketPath:envString}} Database config
     */
    static readDBConfig() {
        let dbConfig;

        let dbConfigString = fs.readFileSync(path.join(Database.dataDir, "db-config.json")).toString("utf-8");
        dbConfig = JSON.parse(dbConfigString);

        if (typeof dbConfig !== "object") {
            throw new Error("Invalid db-config.json, it must be an object");
        }

        if (typeof dbConfig.type !== "string") {
            throw new Error("Invalid db-config.json, type must be a string");
        }
        return dbConfig;
    }

    /**
     * @typedef {string|undefined} envString
     * @param {{type: "sqlite"} | {type:envString, hostname:envString, port:envString, database:envString, username:envString, password:envString, socketPath:envString}} dbConfig the database configuration that should be written
     * @returns {void}
     */
    static writeDBConfig(dbConfig) {
        fs.writeFileSync(path.join(Database.dataDir, "db-config.json"), JSON.stringify(dbConfig, null, 4));
    }

    /**
     * Connect to the database
     * @param {boolean} testMode Should the connection be started in test mode?
     * @param {boolean} autoloadModels Should models be automatically loaded?
     * @param {boolean} noLog Should logs not be output?

View on GitHub (pinned to 6b5ea01557)

Solutions

1. Ensure db-config.json has `"type": "sqlite"` (or "mariadb" / "embedded-mariadb") as a string at the top level.
2. For MariaDB the minimal shape is `{ "type": "mariadb", "hostname": "...", "port": 3306, "database": "...", "username": "...", "password": "..." }`.
3. Recreate the file via the setup wizard if you are unsure of the exact schema.
4. Lint the file: `node -e "const c=require('./data/db-config.json'); console.log(typeof c.type)"` must print 'string'.

Example fix

// before — data/db-config.json
{}

// after
{
    "type": "sqlite"
}

const fs = require("fs"); const path = require("path");
function ensureTypeString(dataDir) {
    const cfg = JSON.parse(fs.readFileSync(path.join(dataDir, "db-config.json"), "utf-8"));
    if (typeof cfg?.type !== "string") {
        throw new Error(`db-config.json: expected 'type' to be a string, got ${typeof cfg?.type}`);
    }
    return cfg;
}

function hasStringType(v) {
    return v !== null && typeof v === "object" && typeof v.type === "string";
}

try {
    dbConfig = Database.readDBConfig();
} catch (e) {
    if (/type must be a string/.test(e.message)) {
        // rewrite db-config.json with the correct type field, then retry
    }
    throw e;
}

When it happens

Trigger: db-config.json exists and is an object but lacks the `type` key (e.g. `{}`); type is set to a non-string; the file was generated by a tool that serialised only connection params and forgot the type discriminator.

Common situations: Custom provisioning scripts that build the config programmatically; manual editing that accidentally deleted the type line; a partial migration that wrote hostname/port but dropped type.

Related errors

• Unknown Database type: ${dbConfig.type}
• Both ${envName} and ${envName}_FILE are set. Please use only
• Failed to read ${envName}_FILE at ${fileValue}: ${err.messag
• Aggregate table migration is already in progress
• Failed to load docker host config

AI-assisted analysis of louislam/uptime-kuma@6b5ea01557 (2026-08-12). Data as JSON: /api/errors/a1da40e9b1882f1c. Report an issue: GitHub.