What is shell exec() function and how to enable or disable it on Linux server?

Shell_exec() :

PHP is an open source scripting language executed on the server and it is used for making dynamic and interactive web pages. It is basically used to develop web-based software applications Web based functionalities, system related scripting and execution features are provided by PHP to develop web application. It runs in many platforms like Windows, Mac OS X, Linux, Ubuntu, etc. It is compatible with all servers and support wide variety of database.

Shell scripts and commands are executed by just requesting a webpage over internet. The web server receive the request and then pass it to PHP interpreter. Special functions are used to run the shell script or command. shell_exec() allows the programmer to execute shell commands in PHP. Shell_exec() command is used to execute commands for server scripts and it returns the output as a string. This command is used to track the real time GPS information and integrate complicated bin-packing algorithms written in PHP. The function will produce an online game that is connected in game server through web browser when it is combined with Ajax and a game engine and avoid Java applets and flash. Though this function, UNIX terminals are used for sending the commands and arguments to software on the server and get the response from the software.

In this technique, the administrator don’t want to login to the server through SSH or other means to run shell commands and scripts on the Server. When the above code is executed, the result will be the host name of the server. Shell_exec() function returns NULL if an error occurs or output is not produced. This function is identical to backtick operator and cannot be executed in safe mode. Commands like “cmd”, “cd” can be executed using this function, but the Perl script cannot be executed.

“Shell_exec() is disabled for security reasons” Warning:

The above warning occurs because shell_exec() is disabled on the server and the function has to be enabled to execute the script completely.

You can disable the “shell_exec()” function from below steps:

• For that login to WHM.
• Click on MultiPHP INI Editor.
• Then go to Editor Mode and choose particular version in which you want to make changes.
• Here find the “disable_functions” and add shell_exec() function to disable the function.

Enabling Shell_exec() Function:

You can disable the “shell_exec()” function from below steps:

• For that login to WHM.
• Click on MultiPHP INI Editor.
• Then go to Editor Mode and choose particular version in which you want to make changes.
• Here find the “disable_functions” and remove the shell_exec() function to enable the function.