1. First enable cgi module using the below lines.
sudo a2enmod cgi
sudo service apache2 restart
After latest apache with cgi mod enabled.
ScriptAlias /cgi-bin/ /usr/lib/cgi-bin/
Options +ExecCGI
AddHandler cgi-script .cgi .pl .py
Options FollowSymLinks
Require all granted
3. Create CGI script
CGI works with multiple languages, but for now we start with bash shell. We will show examples for some other languages later. Here is a simples version of the CGI bash example:
#!/bin/bash
echo "Content-type: text/html"
echo ''
echo 'CGI Bash Example'
Copy the above code and paste it to a new file in /usr/lib/cgi-bin/ called example-bash.sh. Once done make the file executable using thechmod command:
$ sudo chmod 755 /usr/lib/cgi-bin/example-bash.sh
4. View CGI script
All what remains is to navigate with your browser to host-name or IP address of your web server. In our case the URL will be: http://cgi-example.local/cgi-bin/example-bash.sh
You can edit this example to display a disk usage of server's root partition "/". You are only limited by your imagination:
#!/bin/bash
echo "Content-type: text/html"
echo ''
echo 'CGI Bash example
'
echo `df -h / | grep -v Filesystem`
The above code will check for free disk space for a root partition and produce the following page:
5. More CGI examples
As promised, here are more CGI examples for a few more programming languages to get you started.
5.1. Perl
Create and make executable the following /usr/lib/cgi-bin/example-perl.pl with a content:
#!/usr/bin/perl
print "Content-type: text/html\n\n";
print <
CGI Perl Example
CGI Perl Example
CGI Perl Example
htmlcode
5.2. Python
Create and make executable the following /usr/lib/cgi-bin/example-python.py with a content:
CGI Python Example
CGI Python Example
CGI Python Example
"""
5.3. C
For C and C++ to work we will need to have a compiler installed. First, install compiler with:
$ sudo apt-get install build-essential
Once installed create a file example-c.c with the following code:
#include
int main(void)
{
printf("Content-Type: text/plain \n\n");
printf("CGI C Example \n");
}
save the content of example-c.c file and compile it with the following command:
$ sudo gcc -o /usr/lib/cgi-bin/example-c example-c.c
now you should be able to access your C compiled CGI script with: http://cgi-example.local/cgi-bin/example-c
5.4. C++
For C and C++ to work we will need to have a compiler installed. First, install compiler with:
$ sudo apt-get install build-essential
Once installed create a file example-cpp.c with a following code:
#include
using namespace std;
int main()
{
cout << "content-type: text/html" << endl << endl;
cout << "
CGI C++ example
" << endl;
return 0;
}
save the content of example-cpp.c file and compile it with the following command:
$ sudo g++ -o /usr/lib/cgi-bin/example-cpp example-cpp.c
now you should be able to access your C compiled CGI script with: http://cgi-example.local/cgi-bin/example-cpp
6. Conclusion
As mentioned earlier the CGI is quite old and was largely superseded by different programing languages such as PHP, etc. However, as you can see, it is still relatively simple tool to use to automate your Linux administration tasks such as a remote custom monitoring for your Linux servers using a web browser.
https://www.youtube.com/watch?v=ELFdP7eEZ5w
