PHP Warning: shell_exec() has been disabled for security reasons
To start shell command execution in php code you need to edit php.ini and remove "shell_exec" from disable_functions line. below is the example of line
disable_functions = show_source,system,shell_exec,proc_open
to
disable_functions = show_source,system,proc_open
After remove the "shell_exec" save the php.ini file and Restart webserver.
Its done Enjoy !!!! :)