How to enable CGI scripts on Apache

CGI scripts are a practical solution to lighten the load on the Apache web server. The necessary Apache con­fig­ur­a­tions can be set up quickly and the process for granting per­mis­sions for the directory and the CGI files is straight­for­ward.

What are the re­quire­ments for CGI scripts on Apache?

In order to use the Common Gateway Interface (CGI) to submit scripts to your Apache web server, you need the following setup:

• a cloud server or virtual private server (VPS)
• a Linux server dis­tri­bu­tion such as CentOS 8 or Ubuntu 22.04
• an Apache web server that is installed and running

How to enable CGI scripts in the Apache con­fig­ur­a­tions

Two things need to be set up in order to run CGI scripts on a Linux server with Apache:

• Apache needs to be con­figured so the webserver can run CGI scripts.
• The script needs to be uploaded to the correct location and given the correct per­mis­sions.

Apache settings for CGI scripts on CentOS

Open the Apache con­fig­ur­a­tion file httpd.conf for editing:

sudo nano /etc/httpd/conf/httpd.conf

Find the section which reads:

#
# "/var/www/cgi-bin" should be changed to whatever your ScriptAliased
# CGI directory exists, if you have that configured.
#
<Directory "/var/www/cgi-bin">
    AllowOverride None
    Options None
    Require all granted
</Directory>

Replace the line Options None with the following two lines:

Options +ExecCGI
AddHandler cgi-script .cgi .pl .py

The first line tells Apache to execute CGI files that are uploaded to the /var/www/cgi-bin directory. The second line tells Apache that any file ending in .cgi, .pl (Perl script), or .py (Python script) is con­sidered a CGI script.

The section now reads:

#
# "/var/www/cgi-bin" should be changed to whatever your ScriptAliased
# CGI directory exists, if you have that configured.
#
<Directory "/var/www/cgi-bin">
    AllowOverride None
    Options +ExecCGI
    AddHandler cgi-script .cgi .pl
    Require all granted
</Directory>

Save and exit the file. Now restart Apache so that the changes take effect:

sudo systemctl restart httpd

Apache settings for CGI scripts on Ubuntu

On Ubuntu systems such as Ubuntu 22.04, Apache is con­figured by default to allow for the execution of CGI scripts in the des­ig­nated /usr/lib/cgi-bin directory. You don’t need to change any Apache con­fig­ur­a­tions. However, the Apache CGI module must be enabled before CGI scripts can be executed. To do this, you will need to create a symlink (symbolic link):

sudo ln -s /etc/apache2/mods-available/cgi.load /etc/apache2/mods-enabled/

Then restart Apache so that the changes take effect:

sudo systemctl restart apache2

How to upload CGI script and set per­mis­sions

To verify the CGI script func­tion­al­ity on your Apache server, we recommend starting with a test script. Create the file test.cgi in the server’s des­ig­nated cgi-bin and open the test script for editing:

• CentOS: sudo nano /var/www/cgi-bin/test.cgi
• Ubuntu: sudo nano /usr/lib/cgi-bin/test.cgi

Add the following content to this file:

#!/usr/bin/perl
print "Content-type: text/html\n\n"; 
print "<h1>Hello world</h1>";

Save and exit the file. In the next step, give the file the necessaryexecute per­mis­sions:

• CentOS: sudo chmod 755 /var/www/cgi-bin/test.cgi
• Ubuntu: sudo chmod 755 /usr/lib/cgi-bin/test.cgi

View the script in a browser, using either the domain name or IP address:

http://example.com/cgi-bin/test.cgi
http://192.168.0.1/cgi-bin/test.cgi

If the setup was suc­cess­ful, the message ‘Hello world!’ will appear.

How to troubleshoot CGI script errors

404 error: A 404 error means that the URL cannot be found. Check that the script has been added to the right directory.

• CentOS: The default CGI directory is var/www/cgi-bin/
• Ubuntu: The default CGI directory is /usr/lib/cgi-bin

Server 500 error: When error 500 shows up in con­nec­tion with CGI scripts on Apache, it is usually due to the script not having the correct per­mis­sions. Check that the script has execute (chmod 755) per­mis­sions.