`getenv` and `$_SERVER` are two different ways to access environment variables in PHP. It's unusual for `getenv` to not work while `$_SERVER` does, as both methods are commonly used and should retrieve the same value for the `HTTP_HOST` variable.
However, there could be some specific configurations or limitations with your LiteSpeed server that are causing this issue. Here are a few things you can check:
1. PHP SAPI: LiteSpeed supports multiple SAPIs (Server Application Programming Interface) for PHP, such as LSAPI, CGI, or FCGI. Make sure you are using a compatible SAPI that allows `getenv` to work properly. You can check the LiteSpeed configuration or consult the LiteSpeed documentation for more information on the supported SAPIs.
2. LiteSpeed Environment Variables: LiteSpeed has its own set of environment variables that might differ from the standard PHP environment variables. It's possible that `HTTP_HOST` is not available through the `getenv` function but is available through `$_SERVER`. Check the LiteSpeed documentation or consult the LiteSpeed support resources to determine the specific environment variables that are accessible through `getenv`.
3. PHP Configuration: Verify that the PHP configuration on your LiteSpeed server does not have any specific settings or restrictions that affect the behavior of `getenv`. In particular, check the `variables_order` directive in your `php.ini` file to ensure that `E` (Environment) is included. For example: `variables_order = "EGPCS"`.
4. Custom LiteSpeed Configuration: If you have any custom configuration files or rules specific to your LiteSpeed server, check if there are any modifications or restrictions on environment variables that could impact the behavior of `getenv`.
5. Compatibility Issues: It's possible that there could be a compatibility issue between your specific LiteSpeed version and PHP version. Ensure that you are using a compatible combination of LiteSpeed and PHP versions. If there are any known compatibility issues, consult the LiteSpeed documentation or support channels for guidance.
If none of these suggestions resolve the issue, I recommend reaching out to the LiteSpeed support team or community forums for further assistance. They will have more specific knowledge and experience with LiteSpeed server configurations and can help diagnose and resolve the problem.