How to get over 'premature end of script headers' in Apache?

[frodo]

Scenario: running web server (Apache) and web browser on the same machine. (Linux) Perl scripts in under cgi-bin.

With one script in particular, I submit a form, and get "Error 500 - Internal server error". In the Apache error log file I see "Premature end of script headers". I checked the script on Windows Perl Builder; it works there, with no problems. Also, most of the other Perl scripts in cgi-bin run with no problem.

Could the problem be with the Apache configuration?

Originally posted as a Categorized Question.

[davorg]

This message says "your script broke and it didn't send any HTTP headers before sending the error messages". Some suggestions for further investigation:

• Check the error message that was written in your apache error log.
• Switch off output buffering (set $| to a true value) to ensure that headers get out before your errors.
• Put use CGI::Carp qw(fatalsToBrowser) to make debugging easier (but remove it before putting the script live).

[le]

Be sure to send correct HTTP headers:

print "Content-type: text/html\n\n";

or

use CGI;
print header();

[Anonymous Monk]

If you developed this script on Windows, it's possible that the script file has non-UNIX line endings. (The perl interpreter can handle them, but the shebang line is interpreted by the shell, and is not tolerant of incorrect line endings.) If this is the problem, the script may terminate with an error right at the shebang line.

When you bring a script over to UNIX from other OSes, check the file format, and correct line endings if necessary. For example, using vi, when you open the script the file format is displayed at the bottom of the window. To force the file to UNIX format, enter the vi command

:set fileformat:unix

[dondelelcaro]

You can also use cat -A to check the line endings. If you see anything but #!/usr/local/bin/perl$, you've got the wrong line endings, and need to use dos2unix or perl -pi -e 's/\r\n/\n/g' foo.pl.

[Anonymous Monk]

Make sure there's an empty line after the HTTP headers (such as "Content-type:") and before the body text. For example, print "Content-type: text/html\n\n";

Forgetting that empty line will result in a "500 Server Error" being sent to the client, and a "Premature end of script header" message being written to the server error log, so it could be the source of your problem.

[wardk]

For debugging purposes, you can try running the script from the command line; then you will see exactly what the program is outputting.

If using CGI.pm, you can pass in any required parameters to replicate form input:

scriptname fee=fi fo=fum foo=bar

[dragonchild]

That will definitely help, but you need to make sure that the environment is identical to the one the webserver is using. Webserver accounts tend to be very restricted, moreso than human accounts.

[TheThinker]

This can be caused by the suexec wrapper in Apache. Check the suexec logs for the real error message, as the Apache log will only show a generic message.

[Anonymous Monk]

If you are uploading the file to a server via FTP, make sure that you are uploading as ASCII and not binary.

[jundy]

This may seem a little obvious, but make sure that your script produces valid output no matter what the input. (I say this from first-hand experience ;-) Even if you think that you have thought of every conceivable scenario, make sure that you have a default behavior "just in case".

[Anonymous Monk]

Make sure you check /usr/local/bin/perl or whereever your perl file is and make sure that it is executable by the web browser.

Originally posted as a Categorized Answer.

[Anonymous Monk]

Make sure you made the script executable!

Originally posted as a Categorized Answer.

[Mushy]

That only happens when your script had an error in it and perl was not able to compile it successfully. Always test your script first before deploying it as a CGI. perl -c as a minimum.

You could also look at CGI.pm 's fatals_to_browser define.

[tsayman]

Another possibility is to make sure the shebang line isn't indented.

[frodo]

I always do like this

#!/usr/bin/perl
print "Content-type:text/html\n\n";
#html - document itself

It's really shame for me not to use CGI.pm. But I'm too new in Perl programming.

I've checked all my servers log - and only one error is there - "Premature and of script headers". And sometimes I get from perl errors that I'm trying to write on closed handler while it's full nonsense!!!But still he(perl) is writing in them . Bur this is not the main problem. Thank's to davorg - I'kk try everything he said about

Originally posted as a Categorized Answer.

[Anonymous Monk]

Debian users should see if they may be affected by bug #161639.

[frodo]

I always do like this

#!/usr/bin/perl
print "Content-type:text/html\n\n";
#html - document itself

It's really shame for me not to use CGI.pm. But I'm too new in Perl programming.

I've checked all my servers log - and only one error is there - "Premature and of script headers". And sometimes I get from perl errors that I'm trying to write on closed handler while it's full nonsense!!!But still he(perl) is writing in them . Bur this is not the main problem. Thank's to davorg - I'll try everything he said about

Originally posted as a Categorized Answer.

[Anonymous Monk]

Re: How to get over 'premature end of script headers' in Apache?

Originally posted as a Categorized Answer.

[TheThinker]

I had this problem on my site http://www.24by7mall.com and I found it was caused, believe it or not, by a corrupted copy of PERL. Apache was unable to run it successfully. I reinstalled PERL and it worked fine. This was a Deb distro FYI. Hope this helps someone. Took me 2 days to track it down.

Originally posted as a Categorized Answer.

[sherab]

This works on CentOS:

chcon -R -t httpd_sys_content_t /usr/local/web/cgi-bin

It changes security context recursively on /usr/local/web/cgi-bin/.

[mrjcleaver]

My hosting provider mandates that neither the script nor the directory can be group or other writeable. If they are I get the error.

Originally posted as a Categorized Answer.