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Installing Your Own CGI Scripts
Overview
Our Virtual Servers are unique because they provide you with all of the
flexibility, power, and control of a Dedicated Server. Because of this,
you are free to customize and configure your Virtual Server for your specific
circumstance and needs. This includes the ability to install your own custom
developed CGI scripts or CGI scripts that you have downloaded from a third
party source (see CGI
Security Issues).
The "Virtual Environment"
Your Virtual Server services operate in an environment completely separate
of the root system (and any other Virtual Server hosted on the same host
machine). This means that your script does not have access to any files
residing on the root file system, only those files that are located in your
home directory hierarchy.
Path Specification
Because your CGI scripts operate in a "Virtual Environment" (see above),
the pathnames that you specify in your CGI scripts should be declared with
respect to your home directory. For example, your script may access a file
to read from or write to. Instead of specifying a pathname that begins with
/usr/home/LOGIN/usr/local/...,
you would simply use /usr/local/...
instead.
Setting Permissions
After you have uploaded your script or have created it on-line, make sure
you give the script permission to execute. In a UNIX environment, each file
has a specific mode or set of permissions which determine who can read or
write to the file as well as who can execute the file (if anyone). Setting
the "execute bit" on a file is easy to do. You can Telnet
or SSH to your Virtual Server and type the command
where FILENAME
is the name of your script. If a script does not have execute permissions,
your web server will report a "403 Forbidden" server error when it
attempts to execute the script.
Common Problems with
Perl Scripts
- Failure to upload your Perl script in ASCII mode.
Perl scripts, unlike compiled executables, are plain text files. Plain
text files should be transferred from your local computer to your Virtual
Server using ASCII mode (not BINARY mode). Failure to transfer your
Perl scripts to your Virtual Server in ASCII mode may result in 500
Server Errors.
- Improper path specification of Perl interpreter.
The first line of a Perl script indicates the path name of the Perl
interpreter. In the Virtual Server environment, the correct specification
of your Perl 4 interpreter is /usr/bin/perl.
If you downloaded a Perl script from a third party source, the Perl
interpreter is most often defined based on the author's host environment
which may be different from the Virtual Server environment (/usr/bin/perl
is a fairly common however).
- Using a Perl 4 interpreter for a Perl 5 script.
If you have uploaded a Perl 5 script to your Virtual Server, you will
need to install the
Perl 5 interpreter or distribution on your Virtual Server as
well. You would then want to be sure to specify the correct location
of the Perl 5 interpreter in your script - which is /usr/local/bin/perl.
Troubleshooting 500
Server Errors
If you encounter the enigmatic "500 Server Error" when you execute your
scripts, the best way to diagnose the actual source of the problem is to
examine your web server's error log. Your error log is typically stored
in your ~/www/logs
directory under the name error_log.
To review the server error generated in real time, perform the following
steps:
- Telnet or SSH to
your Virtual Server
- Type the following command:
% tail -f
~/www/error_log
The tail command displays the last part of error_log
file and will print anything appended to the error_log
file to your console window. This in effect give you a real time view
of what is being written to your error log file.
- Using your browser, attempt to execute your CGI script again. When
you do this, the actual error message will be displayed in your Telnet
session.
Some commonly encountered errors with their corresponding solutions are
given below.
| Error: |
HTTPd/CGI:
exec of [CGI PATH INFO] failed, errno is 2 |
| Analysis
and Solution: |
| The first line of your
CGI script failed to specify the correct location of the interpreter.
If your script is written in Perl, please see the "Common Problems
with Perl Scripts" section above for the proper first line definition
of the Perl interpreter. If your Perl interpreter definition is
correct, it is very likely that you uploaded the script in BINARY
mode from your Windows machine to your Virtual Server. If you originally
uploaded the script in BINARY mode, re-upload the script in ASCII
mode to correct the problem. |
|
| Error: |
HTTPd:
malformed header from script [CGI PATH INFO] |
| Analysis
and Solution: |
Your script is not printing
out a proper header response. When a CGI is executed, it communicates
back to the web server a message which is divided into two parts:
the header and the body. The header typically tells the web server
the "content type" of the data that will be sent as the body of
the response. The header and body are separated by a single blank
line. An example of a CGI response is shown below:
Content-type: text/html
<html>
<head><title>Title</title></head>
<body bgcolor="white">
Hello world!
</body>
</html>
The "malformed
header from script" error message indicates
that your script is not properly returning the header portion
of the response. You may not have misspelled "Content-type", not
supplied a valid type (such as "text/html"), or failed to print
out a blank line to separate the header from body of the response.
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Overview
