FAQ

# Error Messages - Frequently Asked Questions

What does this error message mean?

# Error Messages

- Invalid argument: core_output_filter: writing data to the network

## Invalid argument: core_output_filter: writing data to the network

Apache uses the `sendfile` syscall on platforms where it is available in order to speed sending of responses. Unfortunately, on some systems, Apache will detect the presence of `sendfile` at compile-time, even when it does not work properly. This happens most frequently when using network or other non-standard file-system.

Symptoms of this problem include the above message in the error log and zero-length responses to non-zero-sized files. The problem generally occurs only for static files, since dynamic content usually does not make use of `sendfile`.

To fix this problem, simply use the EnableSendfile directive to disable `sendfile` for all or part of your server. Also see the EnableMMAP, which can help with similar problems.