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Apache logs End of script output before headers when a CGI process ends before Apache reads its first response header. The message identifies an incomplete CGI response, not the reason it happened. Start by checking what the script writes to standard output, then inspect startup or runtime errors, interpreter configuration, execution permissions, ownership, and any suexec logs.
What the error means
Apache reads a CGI program’s output as a response: headers first, then a blank line, then the response body. In Apache’s source, this exact log message is used when the header scanner reaches the end of the program’s output while it is still waiting for the first header. Apache then returns an internal server error. Apache httpd source
The message does not say why the program produced no header. It may have exited before the response code ran, failed during startup, or been unable to execute in Apache’s environment. A script that runs from a shell is not necessarily running under the same account or policy as the web server.
Check the CGI response format first
CGI output must include a Content-Type header, with a blank line separating the headers from the body. RFC 3875 states that a script “MUST return a Content-Type header field.” RFC 3875: The Common Gateway Interface (CGI) Version 1.1
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Content-Type: text/plain
CGI response bodyUse a content type appropriate to the actual response; text/plain is only an example. Apache’s tutorial shows the same header-then-blank-line pattern. Apache HTTP Server 2.4: Dynamic Content with CGI
Troubleshoot in this order
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Inspect the first output
Check the first bytes and lines written to standard output. The first output must be a valid CGI header, followed by a blank line before the body. Remove debug text, notices, or other output that appears before the header. If the script exits before it reaches the response code, trace the startup path or conditional branch that exits.
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Find errors before the response is written
Review Apache’s error log entries immediately before and after this message. Also check the language’s configured error log or diagnostic destination. Syntax errors, failed initialization, or an exception can stop execution before the script emits a header; the Apache message alone cannot identify which occurred.
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Verify the interpreter and CGI setup
Confirm that the interpreter named in the script’s startup configuration exists at that path on this server, and that CGI is enabled and mapped to the script as intended. Apache’s tutorial illustrates how a script’s first line selects the interpreter. The correct path and handler configuration vary by operating system and server setup.
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Check permissions and runtime ownership
Apache normally runs under an unprivileged account, so a script that works for your login may not be executable by the web server. Check execute permission on the script, directory traversal permission on each parent directory, and ownership against the configured CGI runtime account. If suexec is in use, inspect its log and policy as well. Apache’s CGI tutorial explains the server’s execution context; Plesk’s Linux guidance recommends reviewing
suexec.logand the subscription user’s ownership and execute permissions. Plesk: CGI script returns 500 Internal Server ErrorDo not copy a hosting-panel command or permission change to another server without checking its account model and suexec policy.
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Check line endings if the environment makes this relevant
cPanel documents CRLF line endings as one possible reason a Perl script fails to execute and suggests checking the file type and converting line endings with
dos2unix. Treat this as a provider-specific possibility, not a universal fix for Apache’s message. cPanel: Why do I get a 500 Internal Server Error when my Perl or CGI script runs? -
Use CGI-specific logging when appropriate
Apache’s
ScriptLogdirective can record CGI script errors. It is configured in server or virtual-host context, and its file and directory must be writable by the user running the child process. Follow Apache’s permissions warning; do not make a general log directory broadly writable. Apache mod_cgi: ScriptLogQuick wins for a faster PC:
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Distinguish this from similar Apache messages
End of script output before headersmeans Apache reached the end of output before reading the first header.Premature end of script headersis used when Apache has begun reading headers but the header block ends before it is complete.- A malformed-header error is different again: Apache’s parser reports that when a header line does not contain a colon.
These distinctions describe where response parsing failed; none, by itself, proves a particular script bug or permissions problem. Permission trouble is more plausible when nearby error-log or suexec messages point to execution or ownership.
What to conclude from the log
The error confirms that Apache did not receive a first CGI response header before output ended. A valid response needs a Content-Type header and a blank line before the body, but the underlying cause depends on the script and server context. The actual cause cannot be determined from this message alone; it requires the CGI source, interpreter and Apache configuration, runtime account and permissions, and surrounding logs.
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