Apache Web-Serving with Mac OS X: Part 2by Kevin Hemenway
Editor's note: In his previous article, Apache Web-Serving with Mac OS X: Part 1, Kevin Hemenway showed you how to easily start serving web pages from your Mac OS X computer. In this article, he explores the world of CGI access. To gain the most from what Kevin has to offer here, you'll need some familiarity with the Terminal application. If you haven't explored that feature yet, I recommend that you first read our companion article, Learning the Mac OS X Terminal: Part 1. Once you're comfortable using the command line, you can return here and dig deeper into Apache.
Learning a bit more about Apache
So, after the work we did in the last article, we've got a prettier URL, but still a rather boring site. We need features to impress the boss, and to turn them on we're going to have to start fiddling with Mac OS X's Terminal. We're going to assume you know how to edit and save files via the command line, either through a native shell editor (like vi or emacs) or via a GUI editor such as BBEdit. Our examples below assume BBEdit 6.5 and its shell utility.
Before we turn on features, we need to know where Apache's configuration file lives. To find out, we'll query the Apache web server itself, with the following command line:
This will spit out a screen of information specific to your Apache installation (this will work in any Apache install -- for Mac, Linux, or Windows). On an OS X 10.1.1 machine, we find out that we're using Apache 1.3.20 (in the soon-to-be-released 10.1.2, Apache will be upgraded to 1.3.22.):
Server version: Apache/1.3.20 (Darwin)
As well as where the configuration file is located:
We'll also score two very helpful bits of information:
-D DEFAULT_XFERLOG="/var/log/httpd/access_log" -D DEFAULT_ERRORLOG="/var/log/httpd/error_log"
These are the log files for Apache -- every request and every error message will show up within these logs. You'll find them insanely useful for debugging, as well as making sure our upcoming features are working correctly.
Learning about CGI access
It's now time to fiddle with the most common feature available to a web server: CGI. Without getting overly esoteric, CGI allows us to install thousands of different scripts that can be accessed through a normal web browser. CGI scripts are often written in Perl (also installed by default) and can allow users to access databases, use interactive forms, chat in bulletin boards, and so on.
Apache comes with two simple scripts that can verify CGI is configured correctly. Before we test them, however, let's see what we can learn from the Apache configuration file. To start, open up your config file in your favorite text editor (the example below assumes BBEdit 6.5):
Be forewarned: The Apache configuration file is rather large, but also well documented. Take its introductory warning to heart: "Do not simply read the instructions ... without understanding what they do. They're here only as hints or reminders. If you are unsure consult the online docs. You have been warned." For your own reference, the online docs are available at the Apache web site.
The quickest way to find and learn about the Apache configuration file is to search for the feature you want to enable. In our case, we'll start looking for "CGI". The first entry we find is:
LoadModule cgi_module libexec/httpd/mod_cgi.so
Followed shortly by:
You'll see a number of these lines
within the Apache config file. If you've ever worked with a plug-in-based
program, you'll easily recognize their intent -- these lines load different
features into the Apache web server. Apache calls these "modules", and you'll
see a lot of module names start with
mod_, such as
Lines that are commented out (that is to say lines that are prefaced with a #
character) are inactive.
Because our CGI lines are already active, we'll continue searching:
ScriptAlias /cgi-bin/ "/Library/WebServer/CGI-Executables/" <Directory "/Library/WebServer/CGI-Executables"> AllowOverride None Options None Order allow,deny Allow from all </Directory>
ScriptAlias directive allows us to
map a URL to a location on our hard drive. In this case, Apache is mapping
http://127.0.0.1/cgi-bin/ to the
folder. If you browse to that folder now, you'll see the two CGI scripts I
oft-handedly mentioned above:
isn't that important right now, so we'll move on to our next search
# AddHandler cgi-script .cgi
|Now that we're in a little deeper, let's talk about your Apache experience on Mac OS X.|
is your first major decision concerning your Apache installation. When a
certain directory has been
ScriptAlias'ed (as our CGI-Executables directory
has, above), the files within that directory are always executed as CGI
scripts. If the files were moved out of that directory (say, into our
DocumentRoot directory), they'd be served as normal text files.
uncommenting the above line, you're telling Apache to execute any file that
.cgi. This can happen from any directory and from any user, and is
often considered a security hazard.
In a default installation of Apache on
Mac OS X, CGI scripts are only allowed within
/Library/Webserver/CGI-Executables/. Uncommenting the above line (removing the "#" character) allows CGI scripts to be executed from any user
directory, such as
/Users/morbus/Sites. In our case, because we aren't using the
User directories (because they create ugly URLs for GatesMcFarlaneCo's
intranet), we're going to leave the line commented.
If CGI access
is turned on already, we should be able to reach
http://127.0.0.1/cgi-bin/test-cgi and see a happy result, right? If you
went to that URL, however, you were probably greeted by a not so joyous
response: "FORBIDDEN". Apache screams, "You don't have permission to access
Huh? Why didn't this work? Now is a perfect
time to prove how useful the Apache web server logs can be. If you recall
the results of our
httpd -V command above, Apache's access file is located
/var/log/httpd/access_log. Let's look at the very last lines of that
file, easily reached with this command:
You'll see that the last line looks similar to:
127.0.0.1 - - [19/Nov/2001:21:59:46-0500] "GET /cgi-bin/test-cgi HTTP/1.1" 403 292
Quickly, this line shows where the access request came
127.0.0.1), the time the file was requested, the protocol used
(HTTP/1.1), the response code (403), and the size of the response (292
bytes). This is all fine and dandy, but doesn't tell us what went wrong.
For this, we'll dip into our error log (also pinpointed by the
And we see:
[Mon Nov 19 21:59:46 2001] [error] [client 127.0.0.1] file permissions deny server execution: /Library/WebServer/CGI-Executables/test-cgi
tells us exactly what went wrong -- the file permissions were incorrect.
For Apache to run a CGI script, the script in question needs to have
"execute" permissions. To give the
test-cgi file the correct permissions,
cd /Library/WebServer/CGI-Executables chmod 755 test-cgi
After doing the above, load the URL again, and
you should be happily greeted with gobs of environment information. (To
learn more about permissions, the
chmod utility, and the server
environment, consult your favorite search engine, friendly geek, or
With the basics of CGI out of the way, you can now install CGI-based applications to complement your intranet. Need a content management system for the developers to keep everyone up to date on their coding progress and discussions? Try Movable Type.
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