Apache HTTP Server Version 2.0

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# Error Messages - Frequently Asked Questions

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## Error Messages

- Invalid argument: core_output_filter: writing data to the network
- AcceptEx failed
- Premature end of script headers

### 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.

### AcceptEx Failed

If you get error messages related to the `AcceptEx` syscall on win32, see the `Win32DisableAcceptEx` directive.

### Premature end of script headers

Most problems with CGI scripts result in this message written in the error log together with an `Internal Server Error` delivered to the browser. A guide to helping debug this type of problem is available in the CGI tutorial.

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