CGI Frequently Asked Questions
I'm writing a Perl script. What Perl path should I have at the top of my script?
Your Perl CGI script should begin with:
#!/soft/perl5.8.7-bin/perl -w
I'm writing a Python script. What Python path should I have at the top of my script?
Your Python CGI script should begin with:
#!/soft/python-2.5-bin/python
Why won't my Python .py file execute?
The way our server is configured, you need to name your executable
CGI scripts with the .cgi extension.
How should permissions be set on my CGI script?
- Your home directory should have permissions of 701
-
Your .www (and any sub-directories containing your scripts)
should have permissions of 701
- Your CGI scripts should have permissions of 701
-
Files that your cgi script needs to read (for example an image
file) should have permissions of 604
If you're not sure how to do this, see the
CGI scripting Tutorial for detailed
instructions on setting up a CGI script.
Note: Make sure that your CGI scripts and the
directories that your CGI scripts are in are not group or world
writable, otherwise our server will not execute them.
For security reasons you should never make your files or directories
world writable and you should have a good understanding of
the security implications before you make any files or directories
group writable. This is especially true of web-accessible files and
directories.
Do the owner and group of my CGI script matter?
Yes!
-
The CGI script and the enclosing directory must be owned by you.
-
The group of the file and the enclosing directory must be
the same as your default group.
To find your default group use the
id command. The value returned for gid
will be your default group. (number and name)
Failing to set the owner and group correctly will result in
an Internal Server Error.
How can I tell if my CGI script is producing the correct output?
Run your script from the command line. Simply
cd to the directory containing the
script, and type ./<scriptname.cgi>,
where <scriptname.cgi> is the name
of your CGI script. The first line of output returned should be:
Content-Type: text/html
followed by a newline and then the output of your script. If
the above line is not produced, or it's not followed by a blank
line and then some content, an Internal Server Error will be
displayed. Also, you might find that the script produces the
following prompt when you run it:
(offline mode: enter name=value pairs on standard input)
If this happens, type control-D and the output of the script will
be displayed.
Where can I find the error logs?
Depending on the type of account you have, you can find the
output of the error logs with the following commands:
IT Labs: tail -f /web/logs/www-users.itlabs_error_log/error_log
CS: tail -f /web/logs/www-users.cs_error_log/error_log
The error logs contain the output created when your CGI script
generates an error. The -f flag will
cause the file to remain open and new error messages will be appended
to the terminal output as they are created. This can help you debug
the CGI script.
I'm still getting Internal Server Errors. What else can I do?
First, re-check the answers to the above questions and the steps
outlined in the CGI tutorial.
Most
CGI-related problems are caused by one of the above requirements
not being met. Also, be sure to check the error log to see what
error message is being generated. If you have double-checked the
CGI tutorial and the FAQs on this page
and you are still experiencing problems getting your scripts to
run, contact Systems Staff.
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